TEST: SPL Reducer

 Adjustable load resistor... let's pause for a moment, observe the occasionally pensive faces of the inclined audience... and then shoot from the hip with an explanation. An adjustable load resistor is placed between the power amp and the speaker, converting part or all of the amplifier's output energy into heat. Now, question marks have permanently etched themselves into the incredulous faces of the interested musicians, and an overarching question hangs in the air: what on earth is this good for?

The short answer: Tube amplifiers have the unfortunate habit of only developing their full tonal volume above a certain operating volume. Anyone who has ever stood next to an old non-master full stack being driven into saturation knows what I'm talking about. Along with a maximum of transparency, dynamics, and interaction with the guitar's volume control comes the unfortunate fact that the produced volume is only remotely usable at large open-air events or halls with at least five-digit capacities.

To salvage a maximum of sound without sending one's hearing to the eternal hunting grounds or tempting the FOH engineer to throw hard objects at you, there are the aforementioned products, also known as loadboxes in the Anglo-American realm. Germany's hardware elite forge SPL has also taken on this topic and brings to market the Reducer, a purely passive product that comes without any D.I. function in the style of the Transducer or Cabulator.

Construction

At first glance, one can see the massive construction of the Reducer. Strong, perforated metal sheets as floor and ceiling, along with heat sinks as side panels, allow the heat produced inside to dissipate well. The little box with dimensions of 85 mm x 208 mm x 179 mm rests on 4 massive and expectedly high rubber feet, allowing it to be placed on a head with a carrying handle on the one hand, and not hindering air circulation on the other.

What distinguishes the Reducer from almost all of its competitors is the switchable impedance for the used cabinet. While most loadboxes are designed for a fixed ohm number, here you can choose between the standards 16, 8, and even the less used 4 ohms. In terms of volume reduction, 2 controls share the management. You select a rough pre-setting via the control ranges 0dB, -3dB, -5dB, and "Variable", to then in the last range, starting at -7dB, optionally drive the volume down to infinity. As a very rough orientation, a reduction of 3dB corresponds to approximately halving the volume.

On the rear, there are only 2 jack sockets, whose labeling is readable both regularly and from above. A seemingly small detail, but all the more valuable when you're bending over the amp in the semi-darkness of the stage.

In Practice

The main area of application for the Reducer is likely to be the vintage fraction of the all-tube department, because only here does the reduction of volume, which seems idiotic at first glance, make sense. Highly bred multi-channel amps or even transistor amplifiers will hardly or not at all appreciate the forceful intervention in the master volume.

A vintage amp, however, whose power amp is nicely compressed, whose phase driver is already rattling a bit, and whose power supply is wheezing slightly, can generate the maximum sound here to then tame it with the Reducer. By the way, NEVER fully drive a tube amp, then the amp only sounds harsh, mushy, and indifferent. Forget the old "everything-on-10" myth, that's pure nonsense, a good sound can be achieved up to a maximum of 80% load!

And the sound of the Reducer? If you keep in mind that the subjectively perceived sound always shifts somewhat towards mid-presence with the reduction of volume due to the physical conception of our hearing, and you have to readjust the tone control accordingly, you can only confirm a very good for the Reducer. If you are aware of this circumstance, you will not want to miss the gained dynamics and the increasing pressure of the amplifier.

Expanding on the Technical Aspects

To delve deeper into the technical prowess of the SPL Reducer, it's worth examining some of its key specifications and design features:

1. Power Handling: The Reducer is capable of handling up to 100 watts of continuous power, making it suitable for most guitar amplifiers on the market. This includes vintage classics like the Marshall JMP, modern high-gain monsters, and everything in between.

2. Impedance Switching: As mentioned earlier, the ability to switch between 4, 8, and 16 ohms is a standout feature. This flexibility allows the Reducer to work with virtually any guitar amplifier and speaker cabinet combination. The impedance switch is a robust, high-quality component designed to withstand frequent use without degradation.

3. Attenuation Range: The Reducer offers a wide range of attenuation options. The stepped attenuator provides fixed settings of 0dB (bypass), -3dB, and -5dB. The variable control allows for fine-tuning from -7dB down to complete silence. This range covers everything from subtle volume reduction to silent recording scenarios.

4. Heat Dissipation: One of the critical aspects of any loadbox is its ability to dissipate heat effectively. The Reducer's design incorporates large heatsinks and a perforated casing to ensure optimal airflow. This allows the unit to handle high-powered amplifiers for extended periods without risk of overheating.

5. Passive Design: The Reducer is a completely passive device, meaning it requires no power supply. This not only simplifies setup but also eliminates any potential for added noise or interference that can sometimes occur with active devices.

6. Frequency Response: SPL has designed the Reducer to maintain a flat frequency response across the entire audible spectrum. This ensures that the tonal characteristics of your amplifier are preserved, even when heavily attenuated.

7. Component Quality: SPL is known for using high-grade components in their products, and the Reducer is no exception. The resistive elements are precision-matched and rated for high power handling, ensuring consistency and reliability over time.

Integration into Modern Setups

While the Reducer is primarily designed for traditional tube amplifier setups, its utility extends into modern, hybrid rigs as well. Here are some scenarios where the Reducer can prove invaluable:

1. Home Recording: Many guitarists prefer the sound of a pushed tube amplifier for recording, but achieving this in a home studio environment can be challenging due to volume constraints. The Reducer allows for capturing that sweet spot of tube saturation at manageable volume levels.

2. Live Performance: In smaller venues or on stages with strict volume limitations, the Reducer can help guitarists achieve their preferred tone without overpowering the mix or incurring the wrath of sound engineers.

3. Silent Practice: By using the Reducer in conjunction with a reactive load box or IR (Impulse Response) loader, guitarists can practice silently while still utilizing their favorite amplifier.

4. Amp Modeling: For those using digital modeling systems, the Reducer can be an excellent tool for capturing the power amp characteristics of a real tube amplifier at lower volumes. This can then be fed into an IR loader for a complete "virtual" rig.

Comparison with Active Attenuators

It's worth noting that the SPL Reducer differs from some popular attenuators on the market in that it's a purely passive device. Active attenuators, such as the Universal Audio OX or the Two Notes Torpedo, offer additional features like built-in IR loading, USB connectivity, and even mobile app control. However, these come with their own set of pros and cons:

Pros of Passive Attenuators like the SPL Reducer:
- No need for external power
- Generally more reliable due to simpler design
- Often more transparent in terms of tone
- Usually more affordable

Cons:
- Lack of additional features like IR loading or DI outputs
- No ability to shape the tone beyond attenuation

The choice between active and passive attenuators often comes down to individual needs and preferences. The SPL Reducer caters to purists who want the most direct and transparent path between their amplifier and speaker, with the added benefit of volume control.

Long-term Considerations

When investing in a piece of equipment like the SPL Reducer, it's important to consider its long-term value and usability:

1. Durability: The robust construction and high-quality components used in the Reducer suggest a long operational life. This is particularly important for a passive device that will be handling high power levels and generating significant heat.

2. Resale Value: SPL has a strong reputation in the pro audio world, which often translates to good resale value. Unlike digital devices that can become outdated, a well-designed passive attenuator like the Reducer is likely to remain relevant and desirable for many years.

3. Versatility: The ability to work with different impedances and a wide range of amplifiers means the Reducer can adapt to changes in your rig over time. Whether you're switching between vintage and modern amps or experimenting with different speaker cabinets, the Reducer should remain a useful tool.

4. Maintenance: One advantage of passive devices is their low maintenance requirements. The Reducer should require little more than occasional cleaning and checking of connections to ensure optimal performance.

User Experience and Workflow Integration

The effectiveness of any piece of gear ultimately comes down to how well it integrates into a musician's workflow. The SPL Reducer, with its straightforward design and operation, offers several advantages in this regard:

1. Intuitive Controls: The simple layout of the Reducer means that users can quickly dial in their desired attenuation without navigating complex menus or digital interfaces. This can be particularly valuable in live situations where time and simplicity are of the essence.

2. Transparency: For many guitarists, preserving the natural interaction between their instrument, amplifier, and speaker is crucial. The Reducer's passive design aims to maintain this connection as much as possible, even at reduced volumes.

3. Consistency: Unlike some attenuators that can alter the tonal character of an amplifier differently at various volume levels, the Reducer aims to provide a consistent experience across its attenuation range. This allows users to find their preferred settings and rely on them gig after gig.

4. Flexibility in Placement: The compact size and robust construction of the Reducer allow for flexible placement options. It can be easily integrated into a rack setup, placed on top of an amplifier head, or positioned on the floor near a combo amp.

Potential Limitations and Considerations

While the SPL Reducer offers many benefits, it's important to consider potential limitations or scenarios where alternative solutions might be preferable:

1. Lack of Speaker Simulation: Unlike some high-end attenuators, the Reducer doesn't offer built-in speaker simulation or loadbox functionality for silent recording. Users needing these features would need to combine the Reducer with additional equipment.

2. No Tone Shaping: Some attenuators offer the ability to shape the EQ or add effects. The Reducer's purely passive design means it doesn't provide these options. For some users, this simplicity is a benefit, while others might prefer more tone-sculpting capabilities.

3. Volume Reduction vs. Tone: While the Reducer aims to preserve tone as much as possible, the laws of physics dictate that some changes in perceived tone are inevitable as volume decreases. Users should be prepared to make minor adjustments to their amp settings to compensate for this at lower volumes.

4. Power Handling Limitations: While the 100-watt rating covers most guitar amplifiers, users with very high-powered amps (like some bass rigs) might need to look at alternatives with higher power handling capabilities.

Conclusion

With the Reducer, SPL has a very hot iron in the fire when it comes to loadboxes. Excellent workmanship, outstanding components, and an excellent sound let it leap to the pole position of adjustable load resistors.

The SPL Reducer represents a well-executed implementation of a straightforward concept. It offers guitarists a reliable tool for managing volume while preserving the essential character of their amplifiers. Its simplicity and transparency will appeal to purists who want minimal intervention between their amp and speaker.

While it may lack some of the bells and whistles of more complex attenuation systems, the Reducer excels in its primary function. It's a solution that respects the traditional signal path of guitar, amplifier, and speaker, while providing the crucial ability to manage volume in today's diverse playing environments.

For vintage amp enthusiasts, home recordists, and gigging musicians dealing with volume restrictions, the SPL Reducer offers a compelling option. Its build quality, flexibility, and sound performance position it as a serious contender in the world of guitar attenuators.

Ultimately, the value of the SPL Reducer will be determined by individual needs and preferences. For those seeking a no-frills, high-quality passive attenuator, the Reducer certainly deserves consideration. It stands as a testament to SPL's commitment to sound quality and practical design, offering a solution that bridges the gap between vintage tone and modern volume requirements.

TEST: SPL PQ

 It's always fascinating when two diametrically opposed worlds collide head-on, engaging in their beloved trench warfare. A battle that has been raging for decades now primarily takes place in our beloved recording studios, regardless of their size, level of professionalism, or equipment. We're talking about internal versus external, hardware versus software, or more precisely, outboard gear versus plugins. It's tedious to rehash the oft-cited arguments about price, sound quality, habitus, and the "completely dumbed-down ear of the consumer," which we won't be doing here.

However, a current interim report on the state of play would note the introduction of a new player on the outboard gear team, one that's attracting attention with its massive presence and a very high transfer fee. We're referring to the new flagship from the German 19-inch rack specialist SPL, which is sending the SPL PQ, a formidable colossus, onto the playing field. Let's make way for an equalizer of a very special kind.

Construction

The SPL PQ enters the arena as a mastering stereo equalizer, filling a niche that nowadays is mostly handled entirely digitally within the DAW. Alongside compressors and limiters, all types of EQs are found in the signal chain, at the end of which stands the final stereo file. It's becoming increasingly rare for the sum to be converted again before the final mix and sent through corresponding outboard gear, and when it is, this is usually reserved for more economically advantaged studios. High-quality conversion with appropriate management requires maximum quality in the signal flow to ensure that rerouting the signal is sonically worthwhile and doesn't potentially reduce the quality of the end product. To guarantee this, the product used must possess quite a few features that the plugin armada cannot offer. We're curious to see if it's worth putting down nearly five and a half grand for this top dog.

In terms of dimensions and weight, the SPL PQ falls into the same category as the recently released SPL Iron compressor. Four rack units high and weighing over 15 kilograms, this product, once laboriously unpacked, immediately finds its way into the rack, never to be moved again. As always with SPL, the workmanship is perfect, and the construction is solid down to the last detail. The behemoth is available in black and red.

Controls

Even though the 30 black rotary knobs with 41 detents each, along with 22 push buttons and several mini-switches, might initially leave the user in awe, the SPL PQ appears very familiar, almost "normal" upon second glance. Five fully parametric bands per channel may represent a multiple of what conventional analog equalizers offer the user, but in use, they are virtually self-explanatory. SPL employs their proprietary 120-volt technology, which stands for maximum headroom in the processing and minimal coloration of the signal. Thus, they confront the usual audio circuits, which operate with +/- 15 volts, with an operational amplifier level of +/- 60 volts, which allows for an almost twice as high dynamic range compared to conventional circuits.

As with the SPL Iron, the Stereo Link and Auto-Bypass functions have been integrated into the central control panel, with the latter function deserving special attention. A rotary control allows you to set a time interval at which the SPL PQ automatically switches on and off. This is intended to keep the ear fresh and prevent the switching from being done by hand, which might prepare the ear for the expected difference. A very practical feature.

The Stereo Link switch causes both channels to adopt the settings of the right channel's bypass switch and proportional Q switch. Since the device is essentially designed as a dual mono device, the controls on both sides still need to be adjusted manually. However, this also allows operation as two high-end mono EQs, which will undoubtedly find its application in practice.

A look inside the product makes the German engineer's heart beat faster. Excellent workmanship made in Germany, oversized components like the built-in toroidal transformer, good heat dissipation, and optimal shielding between components speak a clear language. Another special feature is the very large overlap of possible frequencies within the frequency bands. Up to three bands can share and process a specific frequency range.

However, with extreme processing, one should keep an eye on the signal chain after the SPL PQ. Due to the 120-volt technology, the SPL PQ works internally without distortion, but the device does not have an output control. Therefore, one should always keep an eye on the input range behind the EQ to ensure that subsequent products don't negate the painstakingly generated distortion-free signal. However, a toggle switch can, if necessary, quarter the +/- 20 dB level setting, resulting in a +/- 5 dB version.

In Practice

But what good are the best measurements and most massive constructions if the sound doesn't at least somewhat justify the hefty price tag? This brings us to the next dilemma. What does "good sound" even mean? Isn't this ultimately a deeply subjective perception? Aren't we mixing and mastering for a clientele that still attests to a good sound on a thoroughly catastrophically overdriven album like "Death Magnetic"?

Therefore, one should first consider the basic orientation of the SPL PQ. If one wanted to encapsulate the basic sound of the EQ in an adjective, only the word "neutral," paired with "clean," comes to mind. What at first glance seems unbeatable in terms of irrelevance turns out, upon close listening, to be a precision instrument that captures individual frequencies with surgical accuracy and deliberately bends the frequency curves. The targeted saturation with which other devices flatter the ear through overtones and compression will not be found here. The SPL PQ simply has no inherent sound, which cannot be valued highly enough in the realm of a mastering EQ.

Even slight level adjustments have a very strong impact on the overall sound and effortlessly assert themselves in the soundscape. Here, the ability to switch between a "constant" and a "proportional" Q works true musical wonders. This switch influences the bell shape of the Q factor. In the constant Q setting, the Q factor always remains the same, regardless of how much the filter band is boosted or cut. A proportional Q filter, on the other hand, increasingly incorporates neighboring frequencies into the work process with stronger processing, increasing the bell shape. For targeted interventions in the sound image, one will tend to resort to the constant Q variant, while a proportional Q filter works more "musically."

Expanded Technical Specifications

To delve deeper into the technical prowess of the SPL PQ, let's examine some of its key specifications:

1. Frequency Range: The SPL PQ covers an expansive frequency range from 10 Hz to 30 kHz, ensuring that even the most subtle sub-bass and high-frequency details can be manipulated with precision.

2. Filter Types: Each of the five bands per channel offers a choice between peak, high shelf, and low shelf filter types, providing maximum flexibility for shaping the frequency response.

3. Q Factor Range: The Q factor can be adjusted from 0.5 to 15, allowing for extremely narrow surgical cuts or broad, smooth boosts.

4. Gain Range: Each band offers +/- 15 dB of boost or cut, with 0.5 dB increments for fine-tuning.

5. THD+N: Less than 0.001% at +4 dBu input level, showcasing the unit's exceptional clarity and low distortion.

6. Dynamic Range: Greater than 125 dB, thanks to the 120V rail technology, surpassing most digital systems.

7. Frequency Response: +0 / -0.5 dB from 10 Hz to 100 kHz, ensuring transparency across the entire audible spectrum and beyond.

8. Crosstalk: Better than -90 dB at 10 kHz, maintaining excellent channel separation.

9. Input Impedance: 10 kΩ balanced, allowing for easy integration with a wide range of audio equipment.

10. Maximum Input Level: +34 dBu, providing ample headroom for even the hottest signals.

11. Output Impedance: 150 Ω balanced, ensuring optimal signal transfer to subsequent devices.

12. Maximum Output Level: +34 dBu, matching the input capabilities and maintaining signal integrity throughout the chain.

Additional Features and Considerations

The SPL PQ's design philosophy extends beyond mere technical specifications. Its user interface has been meticulously crafted to enhance workflow efficiency in professional mastering environments. The large, easily readable VU meters provide instant visual feedback on signal levels, while the Auto-Bypass function, with its adjustable interval, proves invaluable during extended mastering sessions by combating ear fatigue.

One aspect that sets the SPL PQ apart from many of its competitors is its dual-mono design. This approach allows for true stereo processing when needed, but also opens up possibilities for creative mid-side processing techniques. By treating the left and right channels independently, mastering engineers can address stereo image issues with unprecedented precision.

The unit's build quality deserves further mention. The robust chassis isn't just for show; it provides excellent shielding against electromagnetic interference, a crucial consideration in today's studios filled with potential sources of noise. The high-quality potentiometers and switches are rated for thousands of hours of use, ensuring longevity in demanding professional environments.

Comparison with Digital Alternatives

While the SPL PQ stands as a monument to analog excellence, it's worth considering how it compares to high-end digital equalizers. Many will argue that top-tier plugins can achieve similar results at a fraction of the cost. However, the SPL PQ offers several advantages that are difficult to replicate in the digital domain:

1. Analog Warmth: While the SPL PQ is designed for neutrality, it still imparts a subtle analog character that many find pleasing, especially when pushing the unit to its limits.

2. Tactile Control: The physical interaction with high-quality knobs and switches provides a level of control and connection to the music that many find lacking in mouse-based interfaces.

3. Zero Latency: Unlike digital systems, which introduce some degree of latency, the SPL PQ operates in real-time, allowing for immediate audition of changes.

4. Reliability: With no reliance on computer systems or software updates, the SPL PQ offers a level of stability and longevity that can be appealing in mission-critical studio environments.

5. Resale Value: High-end analog gear often retains its value better than digital alternatives, which can become outdated as technology advances.

Integration into Modern Workflows

Despite its analog nature, the SPL PQ is designed to integrate seamlessly into modern, hybrid studio setups. Its balanced XLR inputs and outputs allow for easy connection to high-end AD/DA converters, enabling its use as an insert in a DAW-based workflow. This flexibility allows engineers to combine the best of both worlds, leveraging the SPL PQ's analog processing alongside digital plugins and editing tools.

For studios working primarily in the digital domain, incorporating the SPL PQ into the signal chain requires careful consideration of the conversion process. The quality of the AD/DA converters used becomes crucial, as any shortcomings in the conversion stage could negate the benefits of the SPL PQ's pristine analog circuitry. This consideration further underscores the importance of viewing the SPL PQ as part of a holistic mastering system rather than an isolated component.

Long-term Considerations

Investing in a piece of equipment like the SPL PQ is a significant decision that goes beyond immediate sonic benefits. Prospective buyers should consider the long-term implications:

1. Maintenance: While built to last, any analog device will require periodic maintenance to ensure optimal performance. Factoring in the cost of professional servicing and potential part replacements is advisable.

2. Future-proofing: As digital technology continues to advance, the question arises of how long top-tier analog gear will remain competitive. However, the enduring appeal of classic analog equipment in many studios suggests that well-designed analog tools like the SPL PQ may have a longer shelf life than some digital alternatives.

3. Training and Familiarity: Mastering engineers accustomed to working entirely in the box may face a learning curve when incorporating the SPL PQ into their workflow. The investment in time to fully understand and leverage the unit's capabilities should be considered part of the overall cost.

4. Client Perception: In some markets, the presence of high-end analog gear like the SPL PQ can be a selling point for a studio, potentially attracting clients who value a hybrid analog/digital approach.

Conclusion

With the SPL PQ, Wolfgang Neumann's team has brought a mastering EQ to market that is poised to overshadow everything that has come before. It's difficult to list points that the SPL PQ wouldn't fulfill or deliver to perfection.

Brilliant detailed solutions, extremely high-quality workmanship, and a sound that can only be described as "outstanding" in terms of flexibility and neutrality leave any doubter sitting mutely in the corner, unless they bring up the eternal topic of retail price.

As always in SPL's high-end range, it's simply pointless to discuss the price, as a true price/performance ratio cannot be established. The device has everything that triggers an official "aha" effect, visually and acoustically; more "showing off" is virtually impossible.

Here, everyone must decide for themselves whether the ultimate sound is worth a price beyond the 5,000 euro mark or not, period. One doesn't discuss with a Tesla driver whether the vehicle represents a real equivalent value for the purchase price.

The SPL PQ represents the pinnacle of analog equalizer design, offering uncompromising sound quality and flexibility for the most demanding mastering applications. Its hefty price tag will undoubtedly limit its accessibility to top-tier professional studios and well-heeled enthusiasts. However, for those who can justify the investment, the SPL PQ promises to be a powerful tool in the pursuit of sonic excellence, capable of imparting that elusive final polish to productions across all genres of music.

Ultimately, the value of the SPL PQ will be determined by the ears and workflows of the engineers who use it. In a world increasingly dominated by digital solutions, it stands as a testament to the enduring appeal of meticulously crafted analog equipment. Whether it becomes a new industry standard or remains a niche product for analog purists, the SPL PQ has undeniably raised the bar for what's possible in the realm of mastering equalizers.

TEST: SPL Phonitor XE

 A review of an SPL product made in Germany is always a particular pleasure for me, not only because of the guaranteed high manufacturing quality but also due to the 50% disapproving comments about the consistently high prices of the Niederkrüchten-based company. The two camps quickly become irreconcilably opposed, essentially repeating their arguments in a mantra-like fashion, with "Product XY is much cheaper and just as good" on one side and "But it's the best there is" on the other. Whether this product will lead to another such discussion remains to be seen in the upcoming test. After all, the SPL Phonitor XE comes with a retail price of €2,099 and, depending on the version, ranks among the top 4 or top 9 most expensive headphone amplifiers in the Thomann music store's portfolio.

The Concept of the SPL Phonitor XE

It's likely known to every reader that SPL has held a firm place in the top league of headphone amplifiers for decades, especially since the Phonitor series secured a permanent spot in many pro studios with the introduction of the legendary matrix circuit. With the SPL Phonitor XE model, SPL is now bringing a new flagship to the market. Unlike its counterpart, the Phonitor X, which can also function as a preamp for signal distribution with its XLR outputs, the XE functions as a pure headphone amplifier. Needless to say, at this price point, the focus is on meeting the highest standards.

The buyer has a choice between two models, with and without a D/A converter, with the integrated DAC768 converter adding €700 to the price. Which model to prefer primarily depends on the personal setup of the studio. If you haven't installed a converter yet, it's worth considering the second variant. Like all other top-tier products from SPL, the SPL Phonitor XE also runs on the patented 120 V technology, which provides a significantly more relaxed headroom during operation.

The fact that SPL has expanded its competencies beyond the pro sector, particularly in the Hi-Fi sector in recent years, is evident in the product's visual appearance, along with the typical "plate feet" that have been used in the Hi-Fi sector for ages. The SPL Phonitor XE thus visually demonstrates its dual orientation, targeting two groups: the pro user in the recording studio and the ambitious Hi-Fi fan. The general visual impression is correspondingly "massive," impressively underlined by a weight of nearly 5 kilograms. For a wider visual selection, the product can be purchased in black, silver, and red to match the respective ambiance.

The first special feature of the SPL Phonitor XE is found on both the front and back of the amplifier in the form of a digital XLR-4 headphone output, which is present along with a standard TRS output. A mini-switch on the front of the housing allows you to choose whether to connect your headphones on the front or the mirrored back. A real blessing when I think about how often the headphone cable stretching across the desk has gotten on my nerves.

The Rear Panel

In terms of connections, SPL exhausts the entire bandwidth, except for the TRS connectors that are almost never used in this segment. For the analog area, there are lockable, balanced XLR sockets in addition to gold-plated RCA connectors (RCA and then gold-plated, actually a contradiction in itself ;-). In the digital realm, the product offers 4 different ways to process the signal with AES, Coaxial, optical, and USB.

The possible conversion rates of the built-in D/A converters from AKM (AK4490) are as follows:

AES/EBU (XLR), PCM sampling rates: 44.1 / 48 / 88.2 / 96 / 176.4 / 192 kHz
Coaxial SPDIF (RCA), PCM sampling rates: 44.1 / 48 / 88.2 / 96 / 176.4 / 192 kHz
Optical SPDIF (Toslink F06), PCM sampling rates: 44.1 / 48 / 88.2 / 96 / with fiber optic < 1m: 176.4 / 192 kHz
USB (B), PCM sampling rates: 44.1 / 48 / 88.2 / 96 / 176.4 / 192 / 352.8 / 384 / 705.6 / 768 kHz
USB (B), DSD over PCM (DoP), sampling rates: 2.8 (DSD64), 5.6 (DSD128), 11.2 (DSD256) MHz

There's also a push button for IR programming, allowing any standard remote control to be used for controlling the headphone amplifier. Additionally, there's the IEC socket, the power switch, and the corresponding voltage selection. To activate the product from the front as well, SPL has installed an additional standby mini-switch on the front panel.

The Front Panel

Always a welcome sight, but besides their retro look, also electronically a highlight for me personally due to their comparatively sluggish response: 2 VU meters, separate for the right and left channels. Depending on the incoming level, the displays can be adjusted in sensitivity by 6 or 12 dB via a mini-switch below the left VU meter. Since the SPL Phonitor XE is designed for the classic solo producer in the studio, the device only has one headphone output each, which can adequately cover headphones in the lower double-digit as well as the higher triple-digit ohm range.

Here's a brief list of the key data for headphone operation:

XLR 4 (digital)
Source impedance: 0.36 Ω
Damping factor (40 Ω): 180
Frequency response (-3 dB): 10 Hz – 300 kHz
Crosstalk (1 kHz): -90 dB
THD + N (10 Hz – 22 kHz, 0 dBu): 0.00082 %
Noise (A-weighted): -98 dBu
Output power (1 kHz, 1% THD, 600 Ω): 2 x 8 W
Output power (1 kHz, 1% THD, 250 Ω): 2 x 3.5 W
Output power (1 kHz, 1% THD, 32 Ω): 2 x 0.7 W
Dynamic range: 130.5 dB

TRS
Source impedance: 0.18 Ω
Damping factor (40 Ω): 180
Frequency response (-3 dB): 10 Hz – 300 kHz
Crosstalk (1 kHz): -90 dB
THD + N (10 Hz – 22 kHz, 0 dBu): 0.00082 %
Noise (A-weighted): -103 dBu
Output power (1 kHz, 1% THD, 600 Ω): 2 x 2.7 W
Output power (1 kHz, 1% THD, 250 Ω): 2 x 5 W
Output power (1 kHz, 1% THD, 32 Ω): 2 x 1 W
Dynamic range: 135.5 dB

The eye-catcher on the front is the Alps-RK27 level control, which turns with the famous "spoon in a honey jar" feel. The left front side is dominated by the input selection and a triple panorama selection (Mono, Stereo, and Laterality with Stereo Sum Panorama rotary control) from the SPL matrix. In this device, the matrix has been limited to the Crossfeed (crosstalk degree of the simulated monitors) and Angle (angle of the stereo triangle) controls. Additionally, the matrix can be switched on and off with a mini-switch. Lastly, the product has two DIP switches on the bottom of the housing, which can be used to adjust the input level for the RCA input (-10dBV/0 dBu) and boost the headphone output with a level increase of 22 dB.

The SPL Phonitor XE in Practice

Let's start with the haptics of the product. As expected, all controls and switches of the SPL Phonitor XE meet the highest standards. The controls are grippy, engage cleanly, and convey a very high-quality feel during switching. The same applies to the switches, which, above all, do not exhibit the notorious "wobble" of less expensive counterparts.

Sonically, the result can be summed up in one word: outstanding! It's hard to put into words how relaxed, detailed, and yet voluminous the SPL Phonitor XE sounds in its entirety. On my Beyerdynamic T1 reference headphones, the amplifier impressed in all aspects and at all volumes. It particularly excelled in terms of dynamics and allowed for relaxed work over several hours without any problems.

A quick word about two special features of the SPL Phonitor XE: the adjustable stereo balance and the matrix. People with hearing impairments will particularly benefit from the Laterality control, as they can find an appropriate stereo center using this control at the first signs of asymmetric deafness. An unusual but very helpful bonus for the affected target group.

The matrix, on the other hand, remains the secret star of the Phonitor series, as it manages to bring together the always unnaturally sounding phantom center of the extreme stereo arrangement of the individual speakers into a naturally sounding result. As is known, there is no situation in nature where a corresponding spatial effect would not be shown due to time delay, which makes the listening pleasure of a signal appear significantly more natural in terms of depth layering. Definitely worth a listen!

Additional Insights

The SPL Phonitor XE's 120V technology deserves a closer look. This patented approach significantly increases the operating voltage compared to standard designs, resulting in several benefits. The higher voltage allows for a larger dynamic range and lower noise floor, which translates to a cleaner, more detailed sound. This is particularly noticeable when listening to complex musical passages or during critical mixing sessions where every nuance matters.

The matrix circuit, a hallmark of SPL's Phonitor series, is more than just a gimmick. It addresses a fundamental issue in headphone listening: the unnatural stereo image that results from having two isolated channels delivered directly to each ear. By simulating the crosstalk and time delays that occur in speaker listening, the matrix creates a more natural, speaker-like experience. This is especially valuable for mixing engineers who need to make critical decisions about stereo placement and depth.

The Laterality control is an often-overlooked feature that can be a game-changer for some users. Beyond its utility for those with hearing impairments, it can be useful in various scenarios. For instance, it can compensate for slight channel imbalances in headphones or recordings, or it can be used creatively to adjust the stereo image without affecting the overall volume.

Build quality is another area where the SPL Phonitor XE shines. The use of high-quality components throughout, from the Alps potentiometer to the gold-plated connectors, ensures not only excellent sound quality but also long-term reliability. The robust construction and attention to detail in the design speak to SPL's commitment to creating professional-grade equipment that can withstand the rigors of daily studio use.

The inclusion of both XLR and TRS headphone outputs provides flexibility for users with different headphone terminations. The ability to switch between front and rear outputs is a thoughtful touch that can significantly improve cable management in cramped studio environments.

While the SPL Phonitor XE is primarily designed for professional use, its features and sound quality make it equally appealing to discerning audiophiles. The combination of high power output, low noise floor, and the unique matrix circuit can breathe new life into high-end headphones, revealing details and nuances that might be missed with lesser amplifiers.

The DAC option is worth considering for those looking to simplify their signal chain or upgrade their digital-to-analog conversion. The AKM AK4490 chip used in the DAC768 version is well-regarded in audiophile circles for its natural, musical sound. Its ability to handle high-resolution PCM and DSD files makes it future-proof for those with extensive digital music libraries.

One potential drawback of the SPL Phonitor XE is its size and weight. While this contributes to its solid build and impressive performance, it may not be ideal for those with limited desk space or who need a more portable solution. However, for those who can accommodate it, the substantial build inspires confidence and helps to isolate the sensitive audio circuitry from external vibrations.

The price point of the SPL Phonitor XE places it firmly in the high-end category, which may put it out of reach for some users. However, when considering its build quality, performance, and unique features, it represents good value for professionals and serious enthusiasts who demand the best possible headphone listening experience.

In the context of SPL's product line, the Phonitor XE represents a sweet spot between the more affordable Phonitor models and the top-of-the-line Phonitor x. It offers most of the features and performance of its more expensive sibling but in a more compact form factor and at a lower price point.

Conclusion

The SPL Phonitor XE once again sets the bar very high for the competition. The amplifier sounds outstanding in all respects, is excellently crafted, and offers two bonus features with the Laterality control and the Matrix circuit, which crown an already very high-quality product.

For professionals working primarily with headphones, the SPL Phonitor XE could be considered an essential tool rather than a luxury. Its ability to provide a speaker-like experience through headphones can significantly improve the accuracy of mixes and reduce ear fatigue during long sessions.

While the price may be a barrier for some, those who invest in the SPL Phonitor XE are likely to find it a long-term solution to their headphone amplification needs. Its versatility, build quality, and unique features make it a product that can grow with the user's needs and continue to provide value for years to come.

In the realm of high-end headphone amplifiers, the SPL Phonitor XE stands out not just for its technical specifications, but for the thoughtful design choices that address real-world needs of audio professionals and enthusiasts alike. It's a product that demonstrates SPL's deep understanding of both the science of audio and the practical needs of its users.

Absolute top class!

TEST: Phonitor 3 DAC

 It is rare for the market leader of a pro-audio product to come from Germany. SPL from Niederkrüchten is one of the representatives that enjoys this honor, especially with their Phonitor headphone amplifier series, which has been occupying the top spots, if not the number one spot worldwide, for years. To maintain this status, the company relies on consistent product maintenance, and this year, the Phonitor series has been updated with the release of version 3, introducing the SPL Phonitor 3 DAC. This review will evaluate whether this product can meet the very high expectations prevalent among professional audio studios and their engineers.

### The Concept of the SPL Phonitor 3 DAC

The SPL Phonitor 3 DAC, developed and manufactured in Germany, serves as the central hub in the studio for headphone operation, while also functioning as a monitor controller for regular monitors. The legendary 120-volt technology is once again employed, which, due to the significantly increased operating voltage, offers higher headroom and generally better measurement values. This is once again attributed to the well-known SUPRA operational amplifier modules. The core of the system is the legendary Phonitor Matrix, which, through a switching process developed by SPL, allows the listening situation under headphones to closely resemble an analog listening situation with monitors. This means that one can work on mixes around the clock, even in rental apartments, and only need to check with real speakers in the final step.

### Construction of the SPL Phonitor 3 DAC

The SPL Phonitor 3 DAC offers the possibility to connect a total of six different sources: 2x analog via XLR 1 and XLR 2, and 4x digital in the form of USB, Coax, Optical, and AES. The sources can be selected using a rotary switch on the front panel at the bottom left. If the single monitor out is not flexible enough for signal output, the expansion rack introduced with the Phonitor 2 can be ordered for an additional cost, increasing the connection capacity to four pairs of speakers.

To optimally represent the digital area, the AK4490 Velvet Sound converter chip from Asahi Kasei Microdevices is used, which was already installed in the highly praised SPL Diamond preamp with 120-volt technology. The AK4490 converts PCM audio with a 32-bit word width and a maximum sampling rate of 768 kilohertz. The AKM converter also supports DSD and processes DSD signals up to a maximum of DSD256.

### Technical Specifications

The amplifier's technical values are impressive, with an output power at the headphone output of 2x 5 watts at 1 kHz, 1% THD, 250 ohms, a frequency range of 10 - 100,000 Hz, and a dynamic range of 134.5 dB. In terms of haptics, the SPL Phonitor 3 DAC might challenge some users. With a weight of 4.15 kilograms and dimensions of 278 mm x 100 mm x 300 mm (W x H x D), it indeed takes up a considerable amount of space on the work surface.

### Front Panel Features

The front panel's eye-catchers include the unnotched and smoothly running ALPS RK27 volume control and the two classic yellow illuminated VU meters, which display the input level in the range of -20 dB to +5 dB. According to SPL, the VU meters meet BBC requirements with a rise time to 0 dB of about 300 ms. The sensitivity of the VU meters can be reduced by 6 or 12 dB using the VU Cal switch due to higher input levels.

The SPL Phonitor 3 DAC features a truly impressive control system with a total of 7 mini switches, 4 rotary switches, and 2 rotary controls, with 3 controls and an additional switch dedicated to managing the Phonitor Matrix. Their individual functions include:

- **Crossfeed:** The 7-step crossfeed switch adjusts the interaural level difference, comparable to the influence of different room sizes and their reflection and absorption characteristics. Since the head reflects and absorbs sound non-linearly, the level difference is frequency-corrected.
- **Angle:** The angle switch, ranging from 15 to 75 degrees, adjusts the interaural time difference, comparable to the setup angle of a pair of speakers. Here too, the level difference is frequency-corrected due to the head's non-linear reflection and absorption of sound.
- **Center:** The 6-step center control adjusts the attenuation of the center signal. When the base width under the headphones is narrowed through crossfeed and angle processing to match speaker playback, the phantom center can become too intense during mixing under headphones. Generally, one tends to lower the center signal, which would create an unbalanced frequency response in speaker playback. The center attenuation allows the center signal to be set in the correct ratio to the stereo signal, ensuring the phantom center is at the correct volume ratio during speaker playback.
- **Matrix Switch:** The matrix switch controls the activity of the matrix circuit (Off = Off), or whether it should work with the center function (All) or without (Cr / A).

### Additional Features

The SPL Phonitor 3 DAC also offers a mono/stereo switch, a solo switch, and a phase switch. The solo switch allows listening to only the left or right channel individually. Since the soloed channel remains on the listening side, this position is also called "Solo-In-Place." If the signal is to be heard in the center ("Solo-To-Center"), the stereo switch is set to mono. This allows for a quick A/B comparison between the two channels. The phase switch inverts the phase of the left or right channel. A known trick involving the combined use of the mono/stereo switch and L/R phase inversion can be used to listen to only the mid or side signal (M/S). In mono mode with active phase inversion for left or right, only the side signal is played back. When phase inversion is turned off, only the mono signal is played back, allowing for a very quick A/B comparison here as well.

A special function is the laterality control, which can be used especially for people with hearing impairments. The laterality control can balance differences in the perception of channel volumes. Unlike a regular balance control, one channel is not only made quieter, but the other is also made louder simultaneously. The control range is much smaller than with conventional balance controls, but it is very finely resolved.

The L/R swap control swaps the L/R in the stereo image, which can be a great help when searching for samples in video soundtracks that should match a scene with a direction of movement. If the direction is not correct, the sample usually has to be loaded into the DAW for channel swapping to assess it. With the L/R swap function, this can be adjusted during pre-listening.

Finally, the SPL Phonitor 3 DAC offers 4 DIP switches on the back, which 1.) boost the headphone output by +12 dB, 2.) activate the Phonitor Matrix for the XLR outputs Preamp Out, 3.) switch the Preamp Out to a Direct Out without volume control, and 4.) activate the Phonitor Matrix for the XLR outputs Direct Out.

### Practical Use of the SPL Phonitor 3 DAC

From the first tones under the headphones, one feels how incredibly "relaxed" the signal playback is due to the 120 V technology. The headroom of the SPL Phonitor 3 DAC is incredible and allows for hours of fatigue-free work due to the highly dynamic playback. Every detail of the incoming signals is captured and reproduced, every dynamic jump is transmitted 1:1 without any compression. The amplifier does not exhibit any form of embellishment in any music genre or speech playback, but it also does not sound too "analytical." The finest resolutions in the voice, outstanding spatial reproduction, and neutral playback across the entire frequency spectrum form the basis for an outstanding product, which in my opinion, once again ranks as the best headphone amplifier worldwide.

The original matrix circuit is still the benchmark for all competitors, but no other provider currently reaches its quality and flexibility in this perfection, making the SPL Phonitor 3 DAC the clear winner in this application area. In fairness, I must admit that I have not heard all the competitors regarding the monitor simulations available on the market, but it is hard for me to believe that the competition could surpass this in this area.

### Conclusion

With the SPL Phonitor 3 DAC, the Niederkrüchten-based company once again proves to be the spearhead in terms of headphone amplifiers. Whether it's the concept, sound, components, or speaker simulation, the SPL Phonitor 3 DAC must be rated with the highest possible score in all respects, once again placing it at the top of the pro headphone amplifier rankings. It doesn't get any better than this!

### Additional Information

To further elaborate on the SPL Phonitor 3 DAC, it is important to highlight its versatility and adaptability in various studio environments. The device's ability to handle multiple input sources, both analog and digital, makes it an indispensable tool for modern audio engineers who often work with a variety of audio formats and sources. The inclusion of high-quality components such as the AK4490 Velvet Sound converter chip ensures that the audio signal is processed with the utmost precision, maintaining the integrity of the original recording.

The Phonitor Matrix, a key feature of the SPL Phonitor 3 DAC, offers unparalleled flexibility in simulating speaker playback through headphones. This is particularly beneficial for audio professionals who need to work in environments where using loudspeakers is not feasible. The matrix allows for accurate spatial representation, making it easier to make critical mixing decisions without the need for constant switching between headphones and speakers.

Moreover, the build quality of the SPL Phonitor 3 DAC is exemplary. The robust construction and high-quality materials used in its design ensure that the device can withstand the rigors of daily studio use. The intuitive layout of the front panel controls, along with the clear and precise VU meters, make it easy for users to monitor and adjust their audio signals with confidence.

In terms of connectivity, the SPL Phonitor 3 DAC is equipped with a wide range of input and output options, making it compatible with virtually any studio setup. The ability to expand the system with additional speaker pairs through the optional expansion rack further enhances its flexibility, allowing users to tailor the system to their specific needs.

The device's ergonomic design also deserves mention. Despite its substantial weight and size, the SPL Phonitor 3 DAC is designed to be user-friendly, with all controls easily accessible and logically arranged. This ensures that users can quickly and efficiently make adjustments without interrupting their workflow.

In conclusion, the SPL Phonitor 3 DAC is a top-tier headphone amplifier and monitor controller that excels in every aspect. Its combination of advanced technology, high-quality components, and user-friendly design makes it an invaluable tool for professional audio engineers. Whether used in a high-end recording studio or a home studio setup, the SPL Phonitor 3 DAC delivers exceptional performance and reliability, solidifying its position as the best headphone amplifier on the market.

The AK4490 Velvet Sound converter chip differs from other converters in several key aspects:

1. High Resolution: The AK4490 can process PCM audio with a 32-bit word width and a maximum sampling rate of 768 kHz. This allows for extremely detailed and precise conversion of digital signals to analog[1].

2. DSD Support: The converter is capable of processing DSD signals up to DSD256. This makes it particularly versatile for high-resolution audio formats[1].

3. Sound Quality: The "Velvet Sound" moniker suggests a particularly smooth and pleasant sound characteristic, often described as natural and musical.

4. Use in High-End Devices: The inclusion of the AK4490 in the SPL Phonitor 3 DAC and previously in the highly praised SPL Diamond preamp demonstrates that this converter is valued for high-quality audio applications[1].

5. Dynamic Range: While not specifically stated for the AK4490, the SPL Phonitor 3 DAC boasts a dynamic range of 134.5 dB, which is exceptionally high and likely attributable in part to the quality of this converter[1].

6. Versatility: The AK4490's ability to handle both high-resolution PCM and DSD formats makes it a versatile choice for a wide range of audio applications.

7. Implementation: In devices like the SPL Phonitor 3 DAC, the AK4490 is implemented alongside other high-quality components, such as the 120-volt technology and SUPRA operational amplifier modules, which together contribute to the overall superior performance[1].

These characteristics make the AK4490 Velvet Sound converter a popular choice for high-end audio equipment, particularly in devices where audio quality is paramount, such as professional-grade headphone amplifiers and DACs.

TEST: SPL Phonitor 2

 A headphone amplifier for nearly 1,300 euros? Anyone who views the SPL Phonitor 2 from this perspective has already lost. Much has been written about monitoring through headphones. Rarely has a topic been so controversially discussed over decades as mixing without proper monitors. Why is that? Wouldn't it be wonderful to work on your individual output anytime, regardless of time and space, entirely according to your personal mood?

This is precisely the goal SPL pursues with its Phonitor series, and now they have brought the successor to Model 1 to market with the SPL Phonitor 2, which boasts some meaningful extensions in addition to its predecessor.

Construction

Why do we actually prefer working with speakers and normally only take headphones on board as a supplement? Well, there are primarily two points that cause problems for the inclined audio engineer when operating purely with headphones. For one, we always perceive music, or all audio signals, in a spatial context, which is not the case with headphone operation. The ultra-stereo setup of headphones at 180 degrees doesn't really occur in nature to this extent and confuses our brain more than it helps. Even the legendary artificial head recordings from several decades ago were characterized by generating the ultimate spatial resolution through headphone operation. A brilliant principle, but one that failed due to the user's inability to handle it.

Furthermore, the majority of our music is still generated for the classic stereo triangle, which spatially cannot be generated in normal headphone operation. Frequency-wise, headphones can already make up a lot of ground depending on the quality level, but the haptics of a recording and especially the depth layering of the spatial image go completely to the dogs here. This is where the first peculiarity of the SPL Phonitor 2 comes in, and explains over the course of the test why one should put down nearly 1,300 € for a headphone amplifier when even every entry-level console nowadays has at least one headphone output.

Speaking of haptics, anyone playing with the thought of acquiring the SPL Phonitor 2 should have a tidy workspace. With dimensions of 305 mm x 277 mm x 99 mm and a hefty weight of 4.3 kilograms, the device spreads a special kind of haptics on its four rubberized aluminum feet. An extremely massive construction, exclusively the best components in the exterior and interior, and a thoroughly noble appearance immediately suggest that this is not just a normal headphone amplifier that simply makes things "loud".

As with many other products, the company from Niederkrüchten also follows the principle of 120-volt technology (symmetrical +/- 60 volts) with the Phonitor 2, which has a significantly better signal-to-noise ratio, higher dynamics, and in particular a larger headroom, making the product sound more "relaxed" in its entirety. Perhaps some of you have already sat under headphones for several hours in an OB van or on other occasions and inevitably experienced fatigue in attention. This is not only due to poorly fitting headphones, but also an operational amplifier that, even if almost inaudibly, constantly works at the limit, straining acoustic perception significantly more than a product that only operates in the middle range.

Unlike its predecessor, which could only manage one stereo source in the input area, the SPL Phonitor 2 can handle three different input sources, making the product also a stereo preamplifier. On the front panel, as with its predecessor, a large volume potentiometer adorns the panel, allowing adjustment from 0 to -97 dB. The special feature, however, is that the control is motorized and can be operated by an infrared remote control if needed via a learning function. Nice for someone who wants to integrate the Phonitor into their Hi-Fi setup, but probably the exception in the studio. Two large, backlit VU meters, which can be switched in input sensitivity between 0, +6dB or +12dB, provide information about the applied level. Overload indicators have been omitted due to the immense headroom of the 120-volt technology.

The sophisticated electronics of the SPL Phonitor 2 can be operated via a total of 7 small toggle switches and 4 additional rotary controls beside the volume control. The Matrix parameters Center, Angle, and Crossfeed quickly attract the user's attention, as this is where the product's special features are bundled. The Angle rotary switch simulates the stereo width of the set-up speaker pair in six different angles (15, 22, 30, 40, 55, 70 degrees). Crossfeed also regulates the crosstalk of the speakers in six stages, while Center regulates the volume of the phantom center to balance the center signals, which are always reproduced a bit quieter in headphone operation. This area alone already shows how elaborately the respective, personal listening experience can be emulated via the preferred monitors.

The Cr/A, off, all toggle switch allows for a quick A/B comparison by activating all three Matrix controls, only Crossfeed and Angle, or deactivating everything. The Solo switch allows you to listen to either the left or right stereo signal individually, optionally Solo-in-Place, or via the activated Mono switch also Solo-in-Center. The Phase switch in combination with the Mono switch also allows you to find phase cancellations very nicely and quickly, without having to struggle through software-based correlation displays. The Laterality control is a very high-quality balance control that, unlike standard versions, has a significantly higher resolution and doesn't regulate down to zero at the stop, which would be pointless in practice anyway.

On the rear, the Phonitor has 2 balanced XLR Left/Right inputs and an XLR stereo output. Additionally, the SPL Phonitor 2 has a stereo RCA input compared to its predecessor. There's also a learning switch for the infrared remote control and the IEC socket. On the bottom of the housing are 4 additional mini switches with which you can adjust the output levels. All output levels can optionally be raised by +6dB or +12dB. Switch 3 raises the RCA level from -10dB to studio level 0dB, and switch 4 loops the signal without further processing except for the phase switching to the line output. This circuit is useful if you don't want to use the SPL Phonitor 2 as a preamplifier or monitor controller.

Practice

It's always difficult to capture listening impressions in written form. However, it's particularly difficult when it's not just about the personal listening impression of frequencies, but rather about a dynamic range that also plays out in the operating voltage range. To anticipate, even if the 120-volt technology is often dismissed as esoteric nonsense by some contemporaries, you can hear a clear difference. The sound impression both in near-field playback or in headphone operation is significantly softer and sounds less "strained". Ear fatigue decreases and the overall sound perception itself improves. Truly impressive.

In terms of speaker simulation, however, there's nothing to discuss, as the SPL Phonitor 2 plays in its own league without any competition. Even in the previous version, I was impressed by the truly incomparable ability to very well replicate my preferred near-field monitors, independent of room size and seating position. The unnatural listening behavior via headphones with the center in the head can indeed be individually faded out and processed to the highest degree via the product's matrix, so that mixing via headphones becomes tangible for the first time. Once you've "grasped" the workings of the parameters, you can literally build your own environment using the matrix. All switches result in a practical way of working and offer manifold possibilities for tonal control.

For my part, I find the mere fact that with the SPL Phonitor 2 you have a portable tool at hand that you can take to any studio along with your favorite headphones to be very helpful. If you train your hearing in parallel to your favorite near-field monitors on the aforementioned constellation, you are practically completely independent of the local monitoring situation. The laborious transport of your preferred monitors for rental productions in foreign studios is completely eliminated.

Expanding on the Phonitor 2's Capabilities

While the core features of the Phonitor 2 are impressive, it's worth delving deeper into some of its more nuanced capabilities and how they can benefit various audio professionals.

For mastering engineers, the Phonitor 2 offers a unique opportunity to check how their work translates to headphone listening, an increasingly common consumption method for end-users. The ability to simulate different speaker setups allows for a quick check of how a master might sound on various systems without the need for multiple physical setups.

Recording engineers working on location might find the Phonitor 2 invaluable. When working in acoustically challenging environments, the ability to have a consistent, reliable monitoring solution that simulates a well-tuned control room can be crucial for making informed decisions during recording.

For post-production professionals, particularly those working in film and TV, the Phonitor 2's spatial simulation capabilities could prove useful when working on surround mixes. While not a replacement for a full surround setup, it could provide a useful reference point when a full system isn't available.

Educators in audio engineering programs might consider the Phonitor 2 as a teaching tool. Its ability to switch between standard headphone playback and simulated speaker setups could help students understand the differences between these monitoring methods and develop critical listening skills.

The 120-volt technology employed in the Phonitor 2 deserves further exploration. While the audible benefits are clear, it's worth understanding the technical reasons behind this choice. The higher voltage allows for greater headroom, which means the circuitry is operating well within its capabilities even during peak moments in the audio. This results in lower distortion and a more open, relaxed sound. It's particularly beneficial when dealing with transient-rich material like percussion, where the extra headroom allows for more accurate reproduction of quick, high-energy peaks.

The motorized volume control, while perhaps seeming like a luxury feature, can be quite useful in professional settings. For instance, it allows for precise recall of volume settings, which can be crucial for maintaining consistent monitoring levels across sessions. The ability to control this via remote could be beneficial in certain workflow scenarios, such as when making adjustments from the "sweet spot" in a control room.

The multiple input options on the Phonitor 2 make it more than just a headphone amp. It can serve as a high-quality monitor controller in smaller studio setups. The ability to switch between three different sources could be useful for comparing mixes across different playback devices or for integrating multiple workstations in a single setup.

The VU meters on the Phonitor 2 are more than just visual flair. In an age where many engineers rely heavily on digital meters, having high-quality analog VU meters can provide a different perspective on levels. The ability to adjust the sensitivity of these meters adds to their utility, allowing for precise monitoring across a wide range of input levels.

One aspect of the Phonitor 2 that shouldn't be overlooked is its potential as a reference tool. By providing a consistent listening environment regardless of the physical space, it allows engineers to have a reliable point of comparison. This can be particularly useful when working in multiple studios or when collaborating remotely with other professionals.

The phase and mono switching capabilities of the Phonitor 2, while seemingly simple features, can be powerful diagnostic tools. The ability to quickly check for phase issues or evaluate a mix in mono can save time and help catch problems that might be missed otherwise.

It's worth noting that while the Phonitor 2 excels at speaker simulation, it doesn't address the frequency response characteristics of the headphones themselves. Users will still need to be aware of the specific colorations introduced by their headphones. Some professionals might choose to pair the Phonitor 2 with headphone correction software for a more complete solution.

For those working with binaural or immersive audio content, the Phonitor 2's crossfeed and speaker angle controls could prove invaluable. These features allow for fine-tuning of spatial perception, which could be crucial when crafting or evaluating 3D audio experiences.

The build quality of the Phonitor 2 is worth emphasizing. In an industry where equipment often needs to withstand the rigors of regular studio use or frequent transportation, the robust construction of the Phonitor 2 is a significant advantage. The use of high-quality components throughout suggests that this is a piece of equipment built to last, potentially offering better long-term value despite its higher initial cost.

When considering the Phonitor 2, it's important to view it as part of a larger monitoring strategy rather than a complete solution in itself. It complements rather than replaces traditional speakers, and its true value becomes apparent when used in conjunction with well-understood headphones and in comparison with other monitoring options.

The potential impact on workflow shouldn't be underestimated. By providing a consistent, speaker-like reference point, the Phonitor 2 could allow for more efficient use of time when working away from a main studio. This could be particularly valuable for producers and engineers who split their time between multiple workspaces or who often need to make critical decisions outside of their primary environment.

Conclusion

With the SPL Phonitor 2, SPL has a product on the market that continues to cover an area without competition, the practicality of which cannot be rated highly enough. In addition to its function as an excellent preamplifier in 120-volt technology, it is particularly the outstanding function of speaker simulation that catapults the product into a league of its own.

In conjunction with high-quality headphones, the product enables an unprecedented variety of design in terms of monitor imaging, which can be managed entirely according to personal taste. After an appropriate familiarization period, rooms, times, monitor manufacturers, and seating positions no longer play a role and enable the sound engineer unprecedented possibilities in terms of productivity.

A discussion about the price of the product can be confidently spared. A product that is not only developed in Germany but also completely manufactured there and additionally equipped with only the best components in every respect cannot be produced more cheaply under these circumstances. The only question that remains is whether one has this budget available, but not whether the product is "worth" the price.

Absolute top class!

In the broader context of audio technology, the Phonitor 2 represents an interesting bridge between traditional speaker-based monitoring and the increasing prevalence of headphone use in professional audio. As more content is consumed via headphones, tools like the Phonitor 2 may become increasingly relevant in ensuring that mixes translate well across various playback systems.

It's also worth considering the Phonitor 2 in light of emerging immersive audio formats. As technologies like Dolby Atmos and Sony 360 Reality Audio gain traction, tools that can accurately represent spatial audio information over headphones may become increasingly valuable. While the Phonitor 2 is primarily designed for stereo content, its underlying technology could potentially be adapted or expanded to address these new formats in the future.

Ultimately, the SPL Phonitor 2 is a specialized tool that addresses a specific need in the audio production world. Its value will depend largely on individual workflows and requirements. For those who frequently work on headphones or need a reliable reference when away from their main monitoring setup, the Phonitor 2 could be a game-changing addition to their toolkit. For others, it may be an interesting but non-essential luxury.

As with any audio tool, the true test of the Phonitor 2 will be in its long-term use across a variety of projects. Initial impressions are certainly positive, but its real worth will be determined by how it influences the quality and efficiency of users' work over time. For now, it stands as an intriguing and innovative approach to a long-standing challenge in audio production.

TEST: SPL Phonitor

 When I first encountered the product description for the SPL Phonitor, I was immediately struck by a mixture of great hope and perhaps even greater skepticism. Why am I making such a fuss about this product? Well, if SPL manages to achieve their stated goal with the Phonitor, we'd be dealing with a revolutionary invention that a legion of producers, sound engineers, and audio technicians have been waiting for.

Enough with the cliffhanger - what exactly is SPL's goal? Anyone who has ever had the pleasure (and responsibility) of occupying a professional producer's chair knows the problem all too well. While you can confidently determine the frequency relationships and spatial imaging of a signal on your own studio monitors, you face significant challenges when working with unfamiliar monitoring setups in other studios.

The stereo image of an unfamiliar setup is positioned completely differently, frequencies resonate differently or are over/under-emphasized. The room acoustics of the control room do their part to turn the workspace into a natural adversary. Your personal sense of sound goes out the window, and creating the ultimate mix becomes an audio Russian roulette with a maximum 70% hit rate. This is why many producers, myself included, always bring their own reference monitors (not to be confused with "particularly good-sounding" monitors) when working on productions in other studios.

Like many colleagues, I would have loved to create a mix on a proper set of headphones, especially for late-night work at home. However, the sometimes unbalanced sound image and, above all, the complete helplessness regarding spatial localization due to the 180-degree stereo width ("through the head") of the signal has always been a major obstacle.

This is where SPL comes in, promising a device that - to quote - "generates music as it was produced, namely for playback over speakers." I must say, I'm quite intrigued!

Construction:

The Phonitor comes in a half-width 19" rack format (9.5 inches) with a height of 2U. The overall build quality is excellent, with SPL fortunately still adhering to the once highly esteemed "Made in Germany" trademark across the board.

A notable feature is that the Phonitor, like all products in SPL's Mastering Series, is based on 120V technology. A total of nine SUPRA-OPs do their duty in the Phonitor, offering a signal-to-noise ratio of 116 dB and an overload tolerance of 34 dB, resulting in a respectable dynamic range of 150 dB.

At first glance, it's clear that this device doesn't fall into the typical "headphone amplifier" category. Too many switches and controls allow for sound shaping possibilities, in stark contrast to the usually spartanly equipped "normal" headphone amplifiers.

On the front panel, we're greeted by an oversized volume control for the headphones. A Crossfeed control, adjustable in six steps, allows for level-dependent, frequency-dependent simulation of crosstalk between both channels. Changing this value is comparable to altering the room size while maintaining the same speaker setup.

The Speaker Angle control adjusts the frequency-dependent simulation of the stereo base width in terms of timing. Here, an angle between 25 and 75 degrees can be set. The Center Level control adjusts the intensity of the center signals in relation to the Crossfeed and Speaker Angle settings of the stereo signal.

In normal headphone listening experiences, the center signal (phantom center) is usually quieter than the side signals, which appear louder due to the super-stereo effect. The narrowing of the base width through Crossfeed and Speaker Angle can lead to an intensification of the phantom center, which can be very finely reduced using this control.

Two toggle switches allow you to deactivate the Crossfeed/Speaker Angle combination and Center Level, providing a good A/B comparison to a regular headphone amp.

Two large VU meters serve as the visual centerpiece of the Phonitor. The display range extends from -20 dB to +5 dB. If needed, the sensitivity can be reduced by 6 dB, extending the display range to +11 dB. In addition to their needles, the "portholes" also feature a signal LED that indicates the presence of a signal above -22 dB, and an overload LED that activates at +21 dB.

The VU meters can switch between two modes: VU and PPM. In VU mode, the needles show an average level and operate with a rise time of about 300 ms. In PPM (Peak Program Meter) mode, this value is reduced to about 2 ms.

The operation mode of the VU meters and meter calibration are also set using two small switches on the front panel. A DIM switch reduces the monitoring volume by 20 dB. This function is typically used in practice to switch between two defined volumes during mixing.

A Solo switch allows you to listen to the right or left channel individually in Solo-In-Place mode. If you want to listen to the respective channel in Solo-To-Center mode, you must also activate the corresponding Mono switches.

A phase switch allows you to activate the crucial phase inversion, which can flip the phase of either the left or right channel. When the Mono switch is activated simultaneously, a difference can be formed between the two audio channels. What remains is what's present only in the right or left of the stereo image.

On the rear panel, the Phonitor features XLR Left/Right inputs and outputs. The input signal passes unchanged to the output sockets, so no monitor output is lost. Additionally, there's a ground lift switch, a voltage selector switch, and an IEC power connector.

In Practice:

After powering on the Phonitor, the VU meters light up, indicating its operational state. Following the manual, I carefully work my way through the parameters, constantly comparing the headphone signal with the "real" monitors.

You wouldn't believe it, but with meticulous adjustment of the parameters, depending on your own monitoring setup, you can actually generate a true-to-life representation of your speakers. I'm completely thrilled! Admittedly, you should set aside several hours and initially focus on understanding the effects of the controls with full concentration. After all, the goal is to "replicate" your own monitoring environment, which can be a real challenge for the uninitiated.

Once you've grasped the workings of the parameters, you can literally build your own environment. All switches provide practical functionality and offer manifold possibilities for tonal control. Only the DIM switch, with its -20 dB reduction, feels a bit too strong for my personal taste, but this is subjective and doesn't detract from the overall impression.

Even with critical listening, I couldn't detect any tonal alterations or losses despite SPL's massive intervention in the phase landscape of the signal.

Expanding on the Phonitor's Capabilities:

While the Phonitor excels at recreating a speaker-like experience through headphones, it's worth delving deeper into its potential applications and how it fits into various workflow scenarios.

For mixing engineers, the Phonitor opens up new possibilities for creating balanced mixes even in less-than-ideal acoustic environments. By simulating a well-tuned control room, it allows for critical decisions on stereo placement, depth, and overall balance without being at the mercy of room acoustics. This can be particularly valuable for those working in home studios or when traveling.

Mastering engineers might find the Phonitor useful as a secondary reference point. While it's not meant to replace high-end speakers in a treated room, it can provide valuable insights into how a mix might translate to headphone listeners. The ability to switch between different speaker angle simulations could help in assessing how a master might sound on various playback systems.

For recording engineers working on location, the Phonitor could serve as a reliable reference when setting up temporary control rooms. Its ability to simulate different speaker setups could help in achieving consistent results across various recording environments.

It's important to note that while the Phonitor excels at creating a speaker-like experience, it doesn't address the frequency response characteristics of the headphones themselves. Users will still need to be intimately familiar with their headphones' sonic signature to make accurate judgments. Some engineers might choose to pair the Phonitor with headphone correction software for a more complete solution.

The Phonitor's VU meters deserve further exploration. In addition to their aesthetic appeal, they serve a practical purpose in gain staging and maintaining consistent levels. The ability to switch between VU and PPM modes allows engineers to monitor both average and peak levels, which can be crucial in maintaining appropriate headroom throughout a mix.

The phase inversion and mono summing capabilities of the Phonitor also warrant attention. These features, while simple in concept, can be powerful diagnostic tools. The ability to flip the phase of one channel and sum to mono can quickly reveal phase issues in a mix, helping to identify problematic frequency cancellations or enhancements.

For those working with binaural or immersive audio content, the Phonitor's crossfeed and speaker angle controls could prove invaluable. By adjusting these parameters, engineers can fine-tune the perceived spaciousness of binaural recordings or assess how well spatial audio content might translate to standard stereo playback.

It's worth considering how the Phonitor fits into the broader ecosystem of headphone-based mixing solutions. While some software plugins attempt to simulate speaker playback through headphones, the Phonitor's hardware approach offers several advantages. There's no latency to contend with, no CPU overhead, and the tactile control over parameters can lead to a more intuitive workflow.

However, the Phonitor is not without its limitations. Its fixed crossfeed curve might not be ideal for all types of program material or headphones. Some users might prefer systems that allow for more customization of the HRTF (Head-Related Transfer Function) used in the crossfeed simulation.

The lack of a built-in DAC might be seen as a drawback by some potential users, especially given the Phonitor's premium positioning. While this allows for greater flexibility in choosing a DAC, it also means an additional component in the signal chain.

For professionals considering the Phonitor, it's important to view it as part of a larger monitoring strategy rather than a complete solution in itself. It complements rather than replaces traditional speakers, and its true value becomes apparent when used in conjunction with well-understood headphones and in comparison with other monitoring options.

The Phonitor's potential impact on workflow shouldn't be underestimated. By providing a consistent, speaker-like reference point, it could allow for more efficient use of time when working away from a main studio. This could be particularly valuable for producers and engineers who split their time between multiple workspaces or who often need to make critical decisions outside of their primary environment.

In educational settings, the Phonitor could serve as a valuable tool for teaching critical listening skills. Its ability to switch between standard headphone playback and simulated speaker playback could help students understand the differences between these two monitoring paradigms and develop a more nuanced understanding of stereo imaging and mix translation.

Conclusion:

Well, I'll be damned! I wouldn't have thought it possible, but I'm actually hearing the stereo image of my monitors through my headphones! Finally, a way to precisely position instruments in the stereo field, even when only headphones are available. SPL has truly created an outstanding product here!

This opens up entirely new avenues for production. For example, you could set up sounds and frequencies in the studio during the day, take the production home on a hard drive, and finish the mix in terms of soundstage, etc., in your home office in the evening if necessary. Words like flexibility and independence come to mind. It's a real boon for anyone who still makes the effort to deliver high-quality productions in the age of "no-budget-over-virtual-knock-me-dead-simulator-cobbled-together-and-mixed-in-the-bedroom" subpar productions.

However, if you now believe you can set up EVERYTHING using the Phonitor, please keep in mind that to work exclusively with the Phonitor, you must know your headphones PERFECTLY in terms of frequency response, etc. The Phonitor only handles the stereo image; you're still listening through headphones, which have their own sound!

By the way, the extent to which music fans will be able to aurally grasp and appreciate this extra effort remains to be seen. I recently saw kids strolling through town with mono headphones that had the frequency response of a megaphone...

In the broader context of audio technology, the Phonitor represents an interesting bridge between traditional speaker-based monitoring and the increasing prevalence of headphone use in professional audio. As more content is consumed via headphones, tools like the Phonitor may become increasingly relevant in ensuring that mixes translate well across various playback systems.

It's also worth considering the Phonitor in light of emerging immersive audio formats. As technologies like Dolby Atmos and Sony 360 Reality Audio gain traction, tools that can accurately represent spatial audio information over headphones may become increasingly valuable. While the Phonitor is primarily designed for stereo content, its underlying technology could potentially be adapted or expanded to address these new formats in the future.

Ultimately, the SPL Phonitor is a specialized tool that addresses a specific need in the audio production world. Its value will depend largely on individual workflows and requirements. For those who frequently work on headphones or need a reliable reference when away from their main monitoring setup, the Phonitor could be a game-changing addition to their toolkit. For others, it may be an interesting but non-essential luxury.

As with any audio tool, the true test of the Phonitor will be in its long-term use across a variety of projects. Initial impressions are certainly positive, but its real worth will be determined by how it influences the quality and efficiency of users' work over time. For now, it stands as an intriguing and innovative approach to a long-standing challenge in audio production.

TEST: SPL Passeq

 In today's audio landscape, very few products manage to elicit a respectful "Ohhh" from even the most experienced and jaded producers. While many former giants of studio technology now limit themselves to manufacturing budget interfaces, or lie gutted in the business corner after being bought out and stripped of their expertise, there are still a select few who hold high the flag of high-end outboard gear. They refuse to be deterred from their path despite massive attacks from the plugin market. One such company is undoubtedly SPL from Niederkrüchten, Germany, which has now launched the second generation of the "king of passive equalizers" with the SPL PassEQ.

A Fundamental Question...

Whenever I've tested a product from SPL's high-end hardware portfolio, one could be certain of a particular type of comment. There was always an entry along the lines of "Way too expensive, my XYZ plugin does the same thing and is included in the package." Undoubtedly, the vast majority of productions today are recorded digitally and never leave the digital realm until they're made audible again through analog speakers. Undoubtedly, very good productions can be created this way.

It's also undisputed that for the majority of music listeners, it's completely irrelevant how well a production is mixed and mastered. Issues like the color of their iPhone or "where is there even room for a speaker" are far more important than the charging behavior of capacitors and the saturation characteristics of coils. And you don't sell a single extra unit of CDs or MP3s by switching from "very good" to "phenomenal" sound quality. So why all the fuss?

But when you turn to the small segment of audiophile connoisseurs who not only enjoy the perfection of a flawless production but can also reflect back to a producer/engineer that it's the maximum of what technology can deliver, it's a completely different approach in terms of personal satisfaction. Whether it's Hilti for craftsmen, Tesla in electric vehicle manufacturing, or SPL in the hardware sector, the air gets very thin in this region, and thanks to "Made in Germany," the price tags correspondingly multi-digit. After all, no one is forcing anyone to buy.

The Inner Workings of the SPL PassEQ

The SPL PassEQ Model 1650 / 1654 is the successor to Model 2595. The predecessor was already considered the non plus ultra in the passive filter realm, so its successor will have a hard time raising the bar even further. Like its predecessor, the current SPL PassEQ works with 120V technology, which all SPL products in this price category use. This technology has proven to be significantly superior to the competition, which mostly works with 40V, in terms of dynamic range, distortion threshold, and signal-to-noise ratio.

The SPL PassEQ itself works with 3 filter bands per side for the boost range and 3 bands for the cut range. With 12 switchable frequencies per band, this makes 36 bands for the boost range and 36 bands for the cut range. Compared to its predecessor, the frequencies have been revised once again, and the quality of the frequencies in terms of capacitors, coils, and resistors has been recalibrated. The term "passive" of course only refers to the filter network; the SPL PassEQ naturally also has active components such as make-up amplifiers and the 120V technology.

The Housing of the SPL PassEQ

This product is clearly not built for mobile operation. You wouldn't even want to move this intimidating behemoth with its 10 kg weight and 4U height in the studio, which probably means that you install the SPL PassEQ in the rack once and then never touch it again. It's very convenient that on the rear panel there are only the balanced XLR outputs, the main fuse, a ground lift, and unfortunately also the power switch. This means using a power strip switch or crawling behind the 19" rack before starting production. Depending on which color the customer wants, the product designation varies between 1650 (black) and 1654 (red), a product variation that was also available with the "Iron" compressor.

Conceptually, the SPL PassEQ is a dual mono EQ, with both sides capable of being operated independently. You won't find a stereo link on this product, as it wouldn't be easily implementable with this design. However, since all controls are stepped, stereo operation is very easy, eliminating the fiddly search for identical levels.

Visually, the 14 controls per side are arranged in a star shape. According to the manual, the Q factor has been readjusted for each frequency range, with only the high-frequency range having an additional 41-step variable Q value. Even though the SPL PassEQ should generally only be operated by ear, here are the key data of the frequency bands again:

LF- : Low Frequency Cut, Shelving with approx. 6 dB/oct, 30 Hz to 600 Hz, max. 22 dB.
LF+ : Low Frequency Boost, Shelving with approx. 6 dB/oct, 10 Hz to 550 Hz max. 17 dB.
MF- : Mid Frequency Cut, Bell, 200 Hz to 6 kHz, max. 11.5 dB.
MF+ : Mid Frequency Boost, Bell, 220 Hz to 4.8 kHz, max 10 dB.
HF- : High Frequency Cut, Shelving, 580 Hz to 22 kHz, max. 14.5 dB.
HF+: High Frequency Boost, Bell, 5 kHz to 35 kHz, max. 12.5 dB.

As expected, the frequency bands of the adjacent frequency controls overlap, which should be considered in the phase response, but sometimes also opens up interesting sonic aspects.

Two illuminated bypass switches, one for each channel, serve as On/Off switches, plus the well-known SPL feature of Auto Bypass. To keep the ears fresh, when this function is activated, the sound processing is deactivated and reactivated at an adjustable interval to show the engineer the sonic effect compared to the original, without having to leave the sweet spot of the listening position.

The SPL PassEQ comes with a very well-written bilingual operating manual, which not only explains the pure functionality of the product but also generally addresses the different philosophies of filter use, especially the interaction between cutting and boosting frequencies.

The SPL PassEQ in Practice

Although the SPL PassEQ will probably find its main area of application in high-end mastering studios, it can of course also be placed classically in the signal path before conversion to the DAW, put on subgroups, or placed in the mix via AUX paths.

Especially when it comes to subtle modification of the source material, the SPL PassEQ scores across the board. It's hard to describe, but you get the impression that every signal experiences a sonic enhancement as soon as it has passed through the EQ. Be it a subtle tightening of the bass, an elegant peak in the midrange, or some shine in the uppermost treble range, the SPL PassEQ creates an alarming addiction factor that old hands might still remember from using the Aphex Aural Exciter in the eighties. Before you know it, you're sending virtually every signal through the product, and everything that sounded very good untreated until now suddenly seems rather dull and lackluster.

This also shows the strength of the product, which subtly supports strengths in the source material with an unpretentious basic orientation and elegantly conceals flaws. The parallel operation of the 6 filters is truly a powerful tool, although you would have to start with a massively distorted signal to activate all 6 filters simultaneously. Even if you start with a perfect signal, you still want to add a touch of shine in the extreme high-frequency range. It really takes a strong will not to let the SPL PassEQ run always and everywhere.

Expanding on the Technical Aspects

The SPL PassEQ's 120V rail technology is a key factor in its exceptional performance. This high-voltage design allows for significantly more headroom compared to standard 30V or 40V designs. The increased voltage translates directly into improved dynamic range and lower noise floor. In practical terms, this means the PassEQ can handle even the hottest input signals without breaking a sweat, maintaining clarity and definition even during complex processing tasks.

The passive filter networks employed in the PassEQ are another cornerstone of its design philosophy. Unlike active EQ circuits that rely on op-amps for gain, passive EQs use inductors, capacitors, and resistors to shape the frequency response. This approach is often praised for its musical and natural-sounding results, as it avoids potential coloration or distortion introduced by active components.

However, the PassEQ isn't purely passive. It incorporates active make-up gain stages to compensate for the inherent signal loss in passive networks. These gain stages are designed with the same attention to detail as the rest of the unit, ensuring they maintain the clarity and low noise floor of the passive section.

The stepped controls on the PassEQ serve multiple purposes. Beyond facilitating easy recall of settings, they also ensure precise matching between the left and right channels for stereo operation. Each step corresponds to a specific combination of components in the filter network, guaranteeing consistency and repeatability.

Circuit Design and Component Selection

SPL's approach to circuit design and component selection for the PassEQ is meticulous. Every resistor, capacitor, and inductor is chosen not just for its electrical properties, but for its sonic characteristics as well. This level of attention extends to the circuit board layout, where signal path length is minimized and potential sources of interference are carefully isolated.

The capacitors used in the PassEQ's filter networks are a mix of high-grade film and electrolytic types, each chosen for optimal performance in its specific application. The inductors are custom-wound to SPL's exacting specifications, ensuring consistency and minimizing potential sources of distortion.

Even the potentiometers receive special treatment. SPL uses conductive plastic types for their smooth operation and long-term reliability. The stepped nature of the controls is achieved through a combination of the potentiometer itself and a precision resistor network, providing both the tactile feel of a stepped control and the electrical precision required for repeatable settings.

Power Supply Considerations

The power supply of the SPL PassEQ is as carefully engineered as the audio circuitry it supports. A robust toroidal transformer forms the heart of the power supply, chosen for its efficiency and low electromagnetic emissions. Multiple stages of voltage regulation ensure that the 120V rails remain stable under all operating conditions.

Extensive filtering is employed throughout the power supply to minimize any potential noise or ripple that could find its way into the audio path. This includes both traditional passive filtering and active regulation stages.

The ground design of the PassEQ is also noteworthy. A star-grounding scheme is employed to minimize ground loops and reduce the possibility of noise entering the system through shared ground paths. The inclusion of a ground lift switch on the rear panel provides additional flexibility when integrating the PassEQ into complex studio setups.

User Interface and Ergonomics

While the technical performance of the PassEQ is paramount, SPL has not neglected the user experience. The front panel layout, with its star-shaped arrangement of controls, is not just visually striking but also ergonomically efficient. This design allows for quick access to all parameters without the need to hunt through menus or switch between layers.

The illuminated bypass switches serve a dual purpose. Beyond their primary function of engaging or disengaging the EQ, they also provide a clear visual indicator of the unit's status, visible even in dimly lit studio environments.

The Auto Bypass feature is a thoughtful inclusion that speaks to SPL's understanding of the creative process. By automatically toggling the EQ in and out of the signal path at user-defined intervals, it allows for objective comparison between processed and unprocessed audio. This can be invaluable in making fine adjustments and avoiding the pitfall of "EQ creep," where small, incremental changes can lead to over-processing.

Application in Modern Workflows

While the SPL PassEQ is undoubtedly a high-end piece of analog hardware, it's designed with an understanding of modern, hybrid workflows. Its balanced XLR inputs and outputs allow for easy integration with professional audio interfaces, allowing it to be inserted into a DAW session via hardware inserts.

For those working primarily in the box, the PassEQ can serve as a high-quality front end for recording, imparting its character to signals before they enter the digital domain. Alternatively, it can be used as part of a master bus chain, providing that final touch of analog magic to a mix before it's printed.

In mastering applications, the PassEQ truly shines. Its ability to make broad, musical adjustments without introducing artifacts is invaluable when working with full mixes. The overlap between adjacent frequency bands allows for complex tone shaping that can be difficult to achieve with traditional parametric EQs.

The PassEQ in Context

It's worth considering the SPL PassEQ in the broader context of the current audio equipment market. While software plugins have undoubtedly democratized access to high-quality processing, there remains a dedicated segment of the industry that values the unique characteristics of premium analog gear.

The PassEQ represents a significant investment, and it's natural to question whether its performance justifies its price tag, especially in an era where powerful EQ plugins are available at a fraction of the cost. However, it's important to recognize that products like the PassEQ aren't just about achieving a particular frequency response – they're about the entire signal path, the quality of the components, the headroom provided by the 120V design, and the subtle but cumulative effects these factors have on the final sound.

For studios and engineers operating at the highest levels of the industry, where even marginal improvements in sound quality can make a difference, the PassEQ represents a tool that can provide that extra edge. It's not about replacing digital workflows entirely, but about having options and being able to choose the right tool for each specific task.

Conclusion

The SPL PassEQ represents the culmination of decades of analog audio engineering expertise. It's a product that doesn't try to reinvent the wheel but instead refines every aspect of its design to achieve a level of performance that stands out even in the rarefied air of high-end audio equipment.

Its strengths lie in its ability to shape sound in a way that feels organic and musical, free from the artifacts that can sometimes plague digital processing. The PassEQ excels at making broad, sweeping tonal adjustments that enhance the natural character of a sound source, rather than imposing an obvious effect.

However, it's important to approach the PassEQ with realistic expectations. It won't magically transform a poor recording into a masterpiece, nor will it necessarily provide better results than well-designed software in every situation. Its value lies in its unique character, its exceptional build quality, and the subtle but meaningful improvements it can bring to already high-quality audio.

For those operating at the highest levels of audio production, where every decibel counts and the quest for sonic perfection is never-ending, the SPL PassEQ represents a powerful tool in the arsenal. It's a reminder that in the world of audio, there's still room for meticulously crafted hardware alongside cutting-edge digital technology.

Ultimately, the SPL PassEQ is a testament to the enduring appeal of premium analog gear in an increasingly digital world. It's not for everyone, and it doesn't need to be. For those who can appreciate and utilize its capabilities, it offers a level of performance and a particular flavor of sound shaping that stands apart in today's audio landscape.