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.