TEST: SPL Crescendo Duo V2

 When taking a generous look at the landscape of professional microphone preamplifiers, one inevitably concludes that the number of two-channel variants is comparatively small. This is all the more surprising considering the number of signal sources designed for stereo, such as overheads in drum recordings, acoustic guitar recordings, the combination of direct sound with ambience, or orchestral recordings. To be prepared in the high-end sector as well, SPL from Niederkrüchten has a product in its portfolio with the SPL Crescendo duo V2, which is now available in an updated version. Let's not hold back and take a closer look at the new version.

### Construction of the SPL Crescendo duo V2

Unlike the V1 model, which came in silver, the V2 version is delivered in an appealing black, which should seamlessly blend into any studio setup. The product comes in a very robust design and requires a firm grip during transport, with dimensions (W x H x D) of 482 mm x 88 mm x 300 mm and a weight of just over 6 kg. To ensure better air circulation for heat dissipation, the side and top panels of the housing are perforated. Nonetheless, no excessive heat generation is expected, as the maximum power consumption is below 20 watts. Like all SPL Pro devices, this product is manufactured in Germany, where SPL handles both development and production.

The fact that the SPL Crescendo Duo V2 is designed for pure rack operation is evident from the absence of any feet in the delivery package and the lack of any holes drilled in the housing. It is therefore advisable to place the product in the rack immediately upon receipt, as the underside is relatively delicate and prone to scratches.

As mentioned earlier, the SPL Crescendo Duo V2 is a two-channel microphone preamplifier in two rack units, once again equipped with SPL's legendary 120-volt technology. The 120-volt technology involves an SPL-developed circuit that allows the built-in power supply to deliver a DC voltage of +/- 60 volts, which is significantly higher than the standard of other manufacturers. The advantage of this operating voltage is that the products have significantly higher headroom in their signal reproduction and generally sound less fatiguing. To operate the product, SPL had to develop special operational amplifiers, which they also manufacture in-house.

Accordingly, the measured values are already at a very high level and in some cases significantly exceed the capabilities of competitors. With an output level of 32.5 dBu, the product can push the signal significantly when needed, and with a distortion factor of only 0.0036 at 30 dB gain and 0.32 dB at 70 dB gain, the SPL Crescendo duo V2 plays in the top league.

### Front Panel of the Product

The front panel of the product features two identical units, each consisting of a VU meter, a large microphone gain rotary knob, a smaller output rotary knob, and a total of six on-off switches. The functions of the switches and knobs are as follows:

- **48V:** Activates the operating voltage required for condenser microphones, along with a control LED.
- **VU-10:** This switch allows the level displayed in the VU meter to be shifted by -10 dB, which is very practical when using high gain settings.
- **ø:** Activating the polarity inversion switch rotates the polarity of a microphone signal by 180°.
- **HP:** A high-pass filter with 6 dB per octave reduces low-frequency noise below 120 Hz.
- **Mic Gain:** Gain is adjusted using a 12-step switch. The preamplification ranges from +18 dB to +70 dB.
- **PAD:** Activating the PAD reduces the input sensitivity by 20 dB. This makes the preamplifier ideal for input signals with high levels. With the PAD activated and minimal gain, the Crescendo duo is also suitable for line-level input signals.
- **Output:** The switchable output control allows level adjustment to subsequent devices. The adjustment range is +/- 10 dB, resulting in a maximum total gain of 80 dB.

### Rear Panel of the SPL Crescendo duo V2

The rear panel of the SPL Crescendo Duo V2 features a significant bonus in the form of a splitter. The fully balanced XLR inputs and outputs, all lockable, can be doubled and independently output to two different inputs. Fortunately, SPL maintains the practice of making all control elements on the rear of the housing readable even when viewed from above. This feature allows for easy reading of all labels when bending over the rack, a small detail but an incredibly significant help in professional environments.

However, whether placing the on-off switch on the rear panel of the housing was a good choice is debatable. While the product can be turned on and off via a power strip, I prefer having the on-off switch on the front panel to individually manage the power status of the product. To prevent ground loops, the SPL Crescendo Duo V2 is equipped with a ground lift, which can be activated via a push button on the rear panel. Finally, there is a cold appliance socket on the rear panel of the housing.

### SPL Crescendo duo V2 in Practice

Whether one likes it or not, the first visual impression remains a decisive factor for a product. In this regard, SPL has once again done everything right. The consistently black appearance of the product exudes an elegant character, and the tactile impressions left by the knobs and switches are classic "Made in Germany" in the best sense. Sometimes one wishes that competitors would place more emphasis on this type of presentation.

Whether it's the coarse resolution of the gain knob or the fine detents of the output knob, all controls do their job with a tactile feedback or, in the case of the switches, a solid clicking noise that audibly underscores the switch's engagement. This makes working enjoyable!

Even with the first incoming signals, one can feel the impact of the 120-volt technology. Although many critics tirelessly claim that this technology is more of a show element than a real physical advantage, one should test in an A-B comparison how resistant the different products are to overload. Indeed, the headroom of the SPL Crescendo Duo V2 is significantly higher than what one can extract from comparable products in terms of resistance. Fast, hard peaks are very well absorbed and do not interrupt the normal signal flow, as is often the case with other products.

As expected, SPL follows a different approach with its product than the classic British preamplification. Unlike the British approach, where the preamp is often driven hot to add more saturation and compression and then attenuated with the output knob, the SPL Crescendo Duo V2 offers uniform amplification across the entire adjustment range without ultimately coloring the signal.

In doing so, the product sounds neutral in the best sense, applicable to all possible microphone types and line signals. The sound remains consistently transparent and provides an excellent basis for further signal processing. The only thing to watch out for is the output knob, as the SPL Crescendo Duo V2 has truly massive amplification reserves and, if used uncontrollably, can easily overload the input of the next device. In this case, even the best preamplification is useless if it is ruined at the next stage.

To what extent the strong bass boost of a ribbon microphone can be controlled with the built-in high-pass filter depends on the specific microphone type. Therefore, it is always advisable to consider placing an additional equalizer in the signal path to manage the typical sonic characteristics of these microphone types. However, anything beyond ribbon microphones will be output in the highest quality with the best sound and measurement values. Rarely have I come across a preamp that can be used so safely without any risk of misuse.

### Extending the Review with Additional Information

#### Design and Build Quality

The SPL Crescendo duo V2's design reflects the meticulous craftsmanship that goes into its production. The unit's robust build quality is immediately apparent, with a sturdy metal chassis that exudes durability and reliability. The matte black finish not only adds to its aesthetic appeal but also ensures that it can withstand the rigors of daily use in a professional studio environment. Each component, from the knobs to the switches, feels solid and responsive, giving users confidence in the device's longevity.

#### Technical Specifications

The SPL Crescendo duo V2 is equipped with a range of technical features that set it apart from other preamplifiers in its class. Here are some of the key specifications:

- **Frequency Response:** The unit offers an impressive frequency response range of 10 Hz to 200 kHz (-3 dB), ensuring that it can accurately capture the full spectrum of audio signals.
- **Signal-to-Noise Ratio:** With a signal-to-noise ratio of 114 dB (A-weighted), the Crescendo duo V2 delivers exceptionally clean and noise-free audio, crucial for high-fidelity recordings.
- **Input Impedance:** The preamplifier features an input impedance of 10 kOhms, making it compatible with a wide range of microphones and ensuring optimal signal transfer.
- **Output Impedance:** The output impedance of 75 ohms ensures that the signal remains strong and intact when driving long cable runs or multiple devices.

#### Operational Amplifiers

At the heart of the SPL Crescendo duo V2 are the custom-designed operational amplifiers. These op-amps are specifically engineered to handle the high-voltage rails provided by the 120-volt technology. This results in superior linearity and minimal distortion across the entire frequency range. The op-amps are designed to offer fast transient response and low noise, making them ideal for capturing the nuances of complex audio signals.

#### Transformerless Design

The Crescendo duo V2 utilizes a transformerless design, which contributes to its transparent sound quality. Transformers can introduce coloration and phase shift, which, while sometimes desirable, can compromise the neutrality of the signal. By opting for a transformerless approach

, SPL ensures that the Crescendo duo V2 delivers an uncolored and accurate representation of the input signal, preserving its original character and dynamics.

#### Power Supply

The power supply of the SPL Crescendo duo V2 is another critical aspect of its design. The unit features a robust, linear power supply that provides stable and clean power to the internal components. This helps to minimize any potential interference or noise that could degrade the audio quality. The power supply is also designed to handle the demands of the high-voltage circuitry, ensuring consistent performance even under heavy load.

#### Versatility in Application

The versatility of the SPL Crescendo duo V2 makes it suitable for a wide range of applications. Whether you're recording delicate acoustic instruments, powerful vocals, or intricate orchestral arrangements, the Crescendo duo V2 provides the necessary clarity and headroom. Its ability to handle both microphone and line-level signals further expands its usability, making it a valuable tool for any studio setup.

#### Comparisons with Competitors

When compared to other high-end preamplifiers on the market, the SPL Crescendo duo V2 stands out due to its unique combination of features and performance. While many preamplifiers offer excellent sound quality, the Crescendo duo V2's 120-volt technology provides an unparalleled level of headroom and dynamic range. This makes it particularly well-suited for recording sources with high dynamic content, such as percussion or brass instruments.

Additionally, the build quality and attention to detail in the Crescendo duo V2 are superior to many competitors. The solid construction, intuitive interface, and reliable performance make it a preferred choice for professional audio engineers who demand the best from their equipment.

#### User Experience

Feedback from users of the SPL Crescendo duo V2 has been overwhelmingly positive. Many users appreciate the unit's transparent sound and the ease of use provided by the well-designed front panel controls. The high-pass filter and polarity switch are often highlighted as particularly useful features, allowing for quick adjustments to improve the quality of recordings.

Users also commend the preamplifier's ability to handle high gain settings without introducing significant noise or distortion. This makes it ideal for recording quiet sources or capturing fine details in complex mixes. The ability to drive long cable runs without signal degradation is another commonly praised aspect, particularly in larger studio setups where equipment may be spread out.

#### Maintenance and Durability

Given its robust construction, the SPL Crescendo duo V2 requires minimal maintenance. Regular cleaning of the exterior and ensuring proper ventilation to prevent overheating are generally sufficient to keep the unit in top condition. The high-quality components used in the construction are designed to last, reducing the likelihood of breakdowns or the need for repairs.

In the rare event that maintenance is required, SPL provides excellent customer support and service options. The company's reputation for quality and reliability extends to its after-sales support, ensuring that any issues are resolved promptly and professionally.

### Conclusion

With the SPL Crescendo duo V2, the Niederkrüchten-based company has added another acoustic heavyweight to its portfolio. With excellent measurement values, pronounced headroom, and a neutral sound across the entire frequency range, the product provides an excellent foundation for any processing stage that will follow in the signal path.

### Additional Considerations

For potential buyers, the investment in the SPL Crescendo duo V2 is not just in a preamplifier but in a long-term enhancement to their studio's capabilities. The unit's combination of technical excellence, build quality, and versatile application makes it a valuable addition to any professional recording setup. While the upfront cost may be higher than some competitors, the long-term benefits in terms of sound quality and reliability justify the investment.

In conclusion, the SPL Crescendo duo V2 stands out as a top-tier choice for audio professionals seeking the highest quality in microphone preamplification. Its advanced technology, robust design, and superior performance ensure that it will remain a valuable tool in any studio for years to come. Highly recommended for testing or direct purchase!