Meier-Audio Corda Soul

Well, this review has been in the works for far too long. For that I owe Arthur Power at Power Holdings, and Dr Jan Meier my sincerest apologies. I have not been able to write due to severe neuropathy in my hands which renders my fingers numb and I can't feel the keyboard. It has taken me 8-10 months to get on the right medical regimen and then the nerve to start writing again. I have not been paid to write this review, all thoughts are my own and this review will be a mixture of music, sound and technology. Jan Meier maybe the smartest person I have ever met, so I can't pretend to understand everything that he put intellectually into this device. But, I can tell you that I have spent a good year with it, I own it and I consider it to be the best AIO I have ever heard. And I have heard many, including the T+A HA200, Violectric V590 Pro, the Bartok Apex among many others. It is that good. So, before we get started, know that we are talking about one of the truly great pieces of kit I have ever experienced and one that should stand the test of time. Especially with his recent upgrades to MK2, which I will discuss more later.

I only used the Corda Soul for this review, but I used 6 different headphones to learn it and test it. I can say without reservation that it competes with my reference system which consists of a CFA3, Pure BiPolar, Eddie Current Aficionado and Matrix's 10th Anniversary X2 Pure DAC and Streamer.

In addition, the entire time I had the Soul hooked to my Roon NUC10, which enabled me to use Roon as my end point for the Soul.

Headphones used:
1. Final D8K Pro
2. Hifiman HEKv2 Non-Stealth
3. LFF Code X2
4. ZMF Atrium Open
5. ZMF Atrium Closed
6. ZMF Verite Closed



Technology of the Corda Soul:
Jan made the Soul (this is what I will call it from here on out) to be his Opus. The best he could build. So, I will borrow some of Jan's explanations before I head into sound and the functionality of these dials. The front of the Soul has many dials which underpins the flexibility of the amp.

Dials:
Crossfeed:
The left most dial controls Crossfeed. In the upright position, Crossfeed is plain stereo. Turning the dial clockwise activates the headphone Crossfeed (5 notches). Turning the Crossfeed to the left activates the loudspeaker Crossfeed (5 notches). Moving the Crossfeed either right or left will widen the soundstage, especially for loudspeakers that are placed close together.

I am not a 2 Channel listener, so my use case was purely headphones, and I can say without question that the Crossfeed works. I keep it exactly as the picture shows above, 3 notches to the right and the soundstage opens up like a flower in the spring.

Notch Filter:
The 2nd dial has 3 functions.
1. When using for loudspeakers, this dial allows you to optimize the delay time between the direct signal and the Crossfeed.
2 .For headphone use, the dial can control channel balance. This is especially useful for headphones that have extremely difficult Frequencies, like the HD800.
3. Lastly, this dial in stereo or headphone Crossfeed mode, and with the switch to the right in the upper position; the dial controls the central frequency of a 6dB, Q=2 notchfilter. Many (even high-end) headphones do have one or two distinct resonance frequencies in the 6..11 kHz range due to the entrapped air-volume between driver and ear. Proper application of the notch filter will lower the energy at the resonance frequency and our tests (using HD800, HE-500, T1, ...) have shown that this can result in a remarkable improvement of quality of sound.

I must admit that I don't have any headphones that benefit from this dial, so I didn't use it.

Here is another pic to keep us on track...


Bit Perfect:
7 LED's indicate sampling frequency and bit-resolution as we move across the front of the Soul. This is a great help in understanding whether or not you are getting a bit-perfect signal. Especially with computer audio, Roon, or any streamer. when the lights are blue at the frequency being played you know that the Soul is outputting a perfect bitstream.
A toggle to the right of the LED's allows to change the filter settings of the DAC-chip used. One can choose between classic filtering (phase correct, brickwall) and a filter-mode without pre-ringing (with a slightly softer, more analog sound). Honestly, I don't hear a huge difference with filters on any DAC. Maybe it is just me, but I found both filters to sound excellent.

The DAC of the Soul uses 2 WM8741 DAC-chips in dual mono and perfectly symmetrical.

Tone Controls:
There are 4 tone controls which move in .75db increments and allow you to move the frequency by up to 4db in either direction. I asked Jan why 4db and his answer was quite simple. "If you need to move any headphone by more than 4db, then it isn't the right headphone for you". I thought that made a lot of sense. The Tone controls are as follows moving left to right.
1. Increase/decrease frequencies below 170khz
2. Increase/decrease frequencies below 500khz
3. Increase/decrease frequencies above 1.5khz
4. Increase/decrease frequencies above 4.5khz

• The 4th dial also has a de-emphasis control when all the way to the left. It can be used when SPIDF does not add the emphasis information. This is a novel approach and not one used often if ever in headphone amps. The affects of the separate controls are cumulative and only exist in the digital domain. You cannot access the DSP if you are not using the DAC.

All controls have Q=0.5 shelving, Stepsize 0.8 dB, range +/- 4 dB.

I must admit that I am not someone who uses the Tone Controls. I tend to not EQ my headphones. I would rather buy headphones that meet my tuning preferences and look at other ways within my chain to ensure that I have the right balance. Plus, I mostly listen to live music coming straight from the soundboard. So, what the band is hearing, I am hearing. However, for this review I listened to a lot of different music to understand the Soul's flexibility and sonic prowess. Below is a pic of the Soul with my Roon NUC and a 4 TB SSD.



Remaining Dials and Controls:
1. Bottom left you have 2 XLR headphone outputs. The one to the left is at 120 OHM, and the one to the right is at 0 ohm. Plugged into the left output is my cable for my Final D8K Pro.
2. To the right is your digital dial where you get to choose your digital connection of choice. You have 3 coaxial-in, 3 Optical-In, 1 Optical-Out and USB 2.0. I used USB for the entirety of my review.
3. Next to your digital dial are 3 gain switches. Low Z, Medium Z, High Z. I used them all effectively and found no headphone in my stable that needed more power than the Soul could provide.
4. The next dial is your volume dial. The SOUL has a discrete volume control with 64 positions. Typical step size is around 0.8 dB. For visual control the ON-OFF LED of the amp changes it's color/intensity with each step. In addition, The potentiometer is motor-controlled and can be learned to react to any two free buttons on an infrared remote control.
5. Lastly is your on/off button. Fairly simple.

The Back of the Soul:

The rear of the SOUL is pretty straightforward. There are one USB-input (up to 24/192), three optical inputs, three coaxial inputs and one pair of balanced analog inputs. There also is an optical output that provides the processed digital signal so people can use the SOUL as a digital processor only. The SOUL also has balanced volume-controlled outputs and can act as a preamp to drive active loudspeakers or a power amplifier. The SPDIF input signals are decoded and de-jittered by a WM8804 SPDIF-receiver-chip. The clock used is an extremely high-quality TCXO.

Other Technologies:
I must admit, many of these technologies are above my level of expertise, but I will include them so you can see how much thought and expertise was put into this device. For example, the Soul has 275 capacitors. Mostly ceramic, except where it makes the most difference for the sound and for those Jan used Nichicon Golds.

The digital audio signal is then fed into an ADAU1451 DSP for all processing concerning the FF-technique, Crossfeed, channel balance, notchfilter, and tone-controls.

After processing the digital signal is converted to an analog signal using two WM8741 DAC-chips in dual-mono-mode.

Each analog signal (four signals in total as this is a balanced amp) is amplified/buffered by one single amplification stage, using an AD797 opamp (biased into class-A) that is buffered by two BUF634s (in high-current-mode). Volume is set by changing the feedback-resistance of the opamp. This results in a much lower background noise and much lower distortion then using a conventional approach with a potentiometer in front of an amplification stage with fixed amplification factor. This amp is "black", even with the most sensitive headphones.

The USB-input uses the CM6631 from C-Media to receive data in asynchronous mode from your PC. These are then sent in SPDIF-format to the WM8804. The use of extremely high-quality TCXOs guarantee a very jitter-free operation.

The SOUL accepts PCM signals with sampling frequencies of 32, 44.1, 48, 88.2, 96, and 192 kHz. Bit-resolutions up to 24-bit.

DSD-signals and 384 kHz signals can not be processed by the DSP and therefore are not accepted. However, I can tell you being a PCM guy that I cannot hear a difference above 192khz. I just can't. Similar to wine, I can tell the difference between a $10 bottle of wine and a $100 bottle of wine, but I cannot tell the difference between a $100 and a $500 bottle of wine. I just can't and I have 25 yrs of culinary experience.

The amp has four separate switched power supplies. One for the digital section, one for the USB section, and two for the positive and the negative supply lines of the analog amplification stage. Each part electrically isolated. The output of each supply is RC filtered and further down-regulated with the use of analog voltage regulators. There are separate regulators for the opamps and the buffers. This, together with a total of around 70,000 uF (!!!) buffer-capacity results in extremely stable supply voltages. Sound-critical capacitors are Nichicon Fine Gold.

The switched power supplies work with a typical switching frequency of 70 kHz. This is far beyond the limit of human hearing and thus any noise induced by the supplies is inaudible. There is no hum or any noise audible produced by the power supplies. I can attest to this. The Soul is DEAD QUIET!

Great care has been taken in the choice of the components used. Neutrik XLR-sockets, an ALPS potentiometer (although it does not carry an audio-signal) for smooth operation, LORLIN siver-plated rotary switches; sealed relays all contribute to a high life-time-expectancy.

Sound:
I have had the pleasure of using the Soul now for about a year. Since I have owned the Soul, Jan has come out with an upgraded MK2 version. I will get into how I perceive those upgrades in a moment. Most importantly, how does all this technology come together and sound?

Without getting too wordy, just about perfect. The Soul was built to be extremely neutral without the use of all the DSP. Jan is a classical listener and he used much of that type of music and headphones like the Beyerdynamic T1, HE 500, and the HD800 to tune the Soul. Headphones of different tunings and loads to ensure the Soul could handle all headphones you throw at it. The sound is completely grain and etch free. I use it solely as an all in one, which I got for help in reviewing so that I could speak to a large piece of our hobby who uses AIO's for their listening pleasure.

The Soul's tonality is just about perfect. Timbral qualities on MK1 are almost flat neutral. This leads to a very clean bass response that is exactly what the recorded source gives you. The bass is fast, and linear. It gives you exactly what is on the recording. What else can you ask for from your bass? The midrange is articulate and detailed with complete and total accuracy. Guitars, Piano, Organ, Stand Up Bass, all aspects of the midrange are so accurate and just open up through the basses beautiful pocket. The treble is my favorite part of the Soul. It feels like it extends forever and has absolutely no peaks or nodes that bother my finicky ears. I hear slight resonances above 4.5k, but nothing that I would EQ out. In addition, the Soul's ability to accurately depict all instruments leads to near perfect decay. Imaging is spot on. Each instrument can be heard in its exact place on stage. I can close my eyes and hear exactly where the band is and how much room there is between them. Top end resolution is absolutely perfect.



How does the Soul make me feel when listening to it? I always start a new piece of gear with the above song. A song written during Covid by a mult-instrumentalist, Xavier Rudd. The song is uplifting and full of texture and wonder. The Soul brings out every bit of emotion and every aspect of the songs attributes. From bass, to vocals, through to wonderfully subtle drumming and cymbal work. The Soul grabs it all and goes straight to the nape of my neck. It makes me feel alive. I love hearing Xavier's hands as they move across the fretboard, and his vocals are forward, but not overly so. Back up vocals sit right behind my head, showing the Soul's innate sense of image specificity. It makes me feel connected to my music in a way that very few pieces of kit make me feel.

Next, I listened to Beck's Morning Phase. Especially " Morning", "Heart is a Drum" and "Say Goodbye".

These albums highlight what makes the Soul so special. When you can hear every detail, at whatever volume you please and hear exactly as it was recorded, you are on to something special. The Soul highlights Beck's special ability to use texture, tones, and his incredible voice to tell a story. The Soul's ability to grab every bit exactly as it was recorded gives me goose bumps. It is holographic, exactly as Beck wanted it.



From here I decided to see how the Soul does with something simpler. Music that is just a singer and a piano. As of late I have been absolutely in love with Bruce Springsteen's Live Series: Songs on Keys. This is just Bruce, his piano, his superior song writing and it is patched directly out of the soundboard. Therefore, the Soul is playing what Bruce is hearing right through my headphones. From "Independence Day", to "The River" to "Drive All Night", and the most rousing version of "Incident on 57th St" the Soul extracts every last bit of emotion. You can feel the saturation dripping from Bruce's vocals being turned into Resolution with the perfect amount of wetness and grit. For this performance I chose my D8K Pro's. My favorite headphone as the midrange is so musical, detailed and emotive. I felt this would be a great combo being that I am listening to just Bruce's voice, his piano and a slight blend of an audience matrix to make this album a perfect soundboard matrix. But, it didn't matter what headphone I chose, the result was the same. Exquisite tone from the piano and vocals dripping with saturation and the perfect amount of wetness in the resolution which made me feel as if I was sitting right next to Bruce on stage. This was equal with my ZMF AC and VC which imbued an extra touch of holographic timbral qualities. I just couldn't stop listening. One more song, just one more song. Is there any better complement?




What Makes The Soul so Special?
I had the opportunity to go to Canjam in Dallas in November. One of the things I wanted to do was listen to every AIO at the event to see how they compared to the Soul. While the Bartok Apex was equal to the Soul in quality of sound, nothing else was as good. That is how good the Soul sounds. And that is only using the Crossfeed 3 notches to the right to open up the soundstage and ensuring that I am using the right headphone output to maximize the efficiency of the Soul.

The Soul has a reference level DAC that is dual mono, perfectly symmetrical, electrically isolated and has no weaknesses. The amp is reference quality and matches my Eddie Current Aficionado, CFA3 and Mjolnir Pure BiPolar in quality. When you have something that is so well executed, add in DSP for those who like to EQ, you have something that is special. It is the Opus of one of the smartest people in the industry. Bass, Midrange, Treble, Tonality, Timbre and the devices stability makes it an absolute winner. And for only $3500, you won't find a device with more technology or sonic quality.

Meier Corda Soul MK2:
About 3 months ago, Jan reached out to me and told me that he had come up with an upgrade for the Soul. He was calling it MK2 and he wanted to send it to me so that I could decide which I preferred, and to send back the one I didn't. The upgrade costs $350 plus shipping one way. You have to ship it to Jan in Bavaria, and he takes care of the rest.

So, what did he upgrade? Well, he wouldn't tell me. He wanted me to try and figure it out on my own. He did tell me that some would prefer it, and others wouldn't. I can tell you that I prefer it, by a LARGE margin. The differences are subtle, but they are noticeable and genius. Coming from this audio nut who is NOT an engineer or a Dr of Physics like Jan, I still feel I was able to understand what Jan did to make MK2 different and to this audio nut, worth every penny to upgrade.

I decided to put on some jazz and funk to see if I could tell what he changed. So, I put on the following albums...



I went with Red Clay, my all time favorite jazz album and Fela Kuti's album with Roy Ayers. Roy Ayers is the greatest vibraphone player I have heard, and the sounds of his vibraphone are like a waterfall of sound, coupled with the layer and texture of Fela's band were simply astounding on the Soul MK2. As was Red Clay. Freddie's trumpet, Ron Carter's bass, Joe Henderson's Sax, and Herbie's piano were incredible. It was shockingly good. Freddie's trumpet was yet again dripping with saturation. This time I used my HEKv2 Non-Stealth and was treated to a tour de force from my favorite jazz song. Ron's bass is so visceral. As a friend told me once, "Ron has got some seriously deep pockets". The Soul personified my friends exact words. I almost wrote, I couldn't believe what I was hearing, but I was hearing it, so that would be a false statement. It was happening, so believe it. So, what did Jan change?

The changes are subtle, but they make the Soul exponentially better in my opinion. He was able to simultaneously smooth out any edges that may exist (which were very few), add a bit of timbral warmth allowing the Soul's musicality to become even more palpable, and he did this while increasing micro-detail and low level detail. I still don't know what he changed, but I am fairly certain most of the changes were to the DAC, bringing it more technically modern. I guess we will never know exactly what he changed, but it is worth every penny.

Conclusion:
So, how would I characterize the Corda Soul MK1 or MK2? A must have for those who are interested in the best all in one unit for headphone listening that I have heard. It also has a reference level pre-amp taboot. The Soul is musical, clean, and full of life. It makes my music sound exactly as it should, the way it was recorded. And it does this with every headphone I own. Every headphone benefits from the Soul. Every headphone, and every album sounds balanced, stable and exactly as they were built and produced to sound. I am not sure I can say much more. 2 big thumbs up! Thank you, Jan for this incredible musical journey. And thank you to both Arthur Power and Jan for your patience as I learned to cope with my health. I highly recommend the Meier Corda Soul. It is simply brilliant in every possible way.

One Edit to the review: You can buy the Corda Soul 2 different ways. Either through Arthur at https://power-holdings-inc.com/, or through Meier Audio if outside of Power Holdings considerable network.

I use the Corda Soul primarily as a preamplifier in a stereo speaker setup with Purifi-based class D power amplifier with XLR analog inputs and Swedish Marten speakers. The sound quality of Corda Soul in preamplifier use was a big surprise to me, as my previous preamplifier was not bad at all, and with Corda Soul I felt like entering an entirely new level or class in terms of sound quality. That big difference alone would have covered the big price of the unit, and then you have all those DSP controls - and a top class headphone amplifier! Yes, it is primarily designed as headphone amplifier, but in my use case I get even bigger value as a preamplifier. When doing late evening listening it is straightforward to power off the power amp and connect my Focal Clear Mg to continue listening without consideration of sound level disturbing anyone.

I use Corda Soul only with Focal Clear MG headphones via low impedance headphone output. Sound is clear, dynamic and ”embracing”. It is easy to pick any old favorite music album just out of curiosity, i.e. what new I could hear on a familiar album. I am not really able to compare Corda Soul to the higher league competition in the headphone amps market. Simply put, it is hard to imagine what more I could hear from the Focal headphones with any other headphone amplifier. Maybe more bass or more biting guitars with metal music, but that’s about it - and I haven’t really tested the DSP that much yet.

I have also Corda Daccord FF and Corda Jazz FF in a desktop setup, and I can of course say that even though the Daccord has same DAC chips and Jazz has the FF implementation as well, there is obviously improvement in sound quality with Corda Soul. I tested Corda Soul for comparison to the old desktop setup briefly with single-ended cable adapter, using Sennheiser HD660S and Beyerdynamic DT880. I felt that the differences are not so big if using single-ended cables with Corda Soul, still the ”higher league sound” of Corda Soul is noticeable.

Corda Soul sound signature is clearly audible both in headphone use and in loudspeaker use. Clarity is most obvious quality factor, especially with human voices. Bass lines can be easily followed and ”spicy”. Soundstage was greater and more accurate than I could expect, especially with loudspeakers. Higher midrange or treble is not fatiguing at all, and is quite lively and ”sparkling”, highs are popping up and chiming everywhere. Actually, the only doubt I have regarding the sound is whether the treble is natural or there is some excessive ”stardust” or ”FF black magic” involved. I can imagine that because I’m mostly listening to studio music, it can be also the artificial nature of mixes on the records I’m hearing.

Daily use as preamplifier is simple enough, even though this unit is designed more for desktop nearfield use. Teaching your existing IR remote is a nice solution. In short, it was better than I expected. I also realized that the trigger out connection would not help that much, if also using as headphone amplifier, because the power amp would play the same output as the headphone amp. Well, who would have Corda Soul and NOT use it with headphones…Jan also offered to make modification for trigger out if needed. The good thing in preamplifier use is that you can connect virtually all audio with digital inputs, so Corda Soul truly is a capable audio center, with the limitation of manual input selection from front panel. I even connected my 15+ years old Sony CD and MiniDisc players with digital, and the sound is excellent. Additionally, the DSP practically gives EQ functionality to adapt sound to your taste and acoustics. I measured the response in my room using REW and playing with the DSP controls, first settings were quite easily guessed only by reading the manual and remembering the bumps of previous measurements.

Notch filter seems highly valuable for headphone resonant frequency mitigation, in case of Focal Clear Mg I couldn’t hear that big difference, although I didn’t have any clear target frequency. Crossfeed was originally (in the past) something I didn’t like, however nowadays I prefer to listen headphones only with crossfeed. Also, I am not so interested to compare sound qualities by switching between equipment, rather I like to spend time and then get the feeling and impression via longer term sessions. All in all, as this is also top-of-the-line unit, I can’t imagine what other tweaks I would need, even if considering Corda Soul also as a DAC. It has enough inputs and it displays the sample rate. I don’t need DSD, and MQA is already dead to me.

I use mainly MacMini as digital source via Matrix Audio USB bridge and coaxial cable. First tests I did with USB directly from MacMini, and the sound was at least as good, if not better. I prefer to keep a bit isolation in between computer and USB input, but I need to test it out again to be able to say if there is a difference.

Edit: after posting the review, I read older post by Jan explaining the USB input isolation inside Corda Soul. I might later remove the Matrix Audio USB bridge and use the USB input of Corda Soul without additional components.

For vinyl source and analog XLR in the first impressions were not as spectacular as for digital inputs. The sound was at least as good as with my previous preamplifier, and the ”FF black magic” seemed noticeable also in analog. I appreciated the fully balanced design. Nevertheless I need to take more time to play with gains and other system factors.

To sum it up: simply brilliant preamplifier/headphone amplifier! In my viewpoint it provides fantastic value, considering it serves me as a dual-purpose unit. Corda Soul is the best single component upgrade I ever made, after 25+ years in the hi-fi hobby .

I’ve used an Oppo HA-1 as my DAC, preamp and headphone amp for 4 years. I love its clean neutral sound, driving HD-580 and LCD-2 Headhpones, and my Magnepan 3.6/R speakers. Yet I wonder whether better sound could be had.

Jan Meier built 2 Soul prototypes, each of which resembles a science project but is solid, if not elegant, and electrically and sonically equivalent to the production unit. If you contact him you can arrange to borrow the prototype. Jan has a generous policy of not charging to borrow it (though you have to ship it back to him in Germany), and he has a 14-day return policy for the final product.

It may seem unfair to compare the Oppo with the Soul, as the Soul costs several times as much. But the Oppo is what I have, and I’ve always believed, based on comparison with other headphone amps and DACs, that it punches well above its weight class.

From a distance, the Soul & Oppo sound similar, which is expected for DACs that are well engineered with excellent measurements. Both are neutral and transparent. However, the degree of similarity surprised me. I had to listen carefully to specific recordings that I know well, to hear reliable differences. Even then, the differences were subtle--but real, as I confirmed with blind tests. The differences were easier for me to hear on speakers. I suspect this is because my speakers are more neutral and resolving than my headphones. Audeze LCD-2 are great headphones but not as resolving as Magnepan 3.6/R. Most people, especially those with revealing headphones that are harder to drive (like the HD-800), will hear differences more easily on headphones than on speakers.

To characterize the subjective differences is to overstate them. But to summarize:

• Bass: the Oppo has deep, clean bass yet the Soul in comparison makes the Oppo sound just a touch wooly. With excellent recordings of bass drums and violins, the Soul reveals more of the percussive attack/decay and complex timbre.
• Midrange: the Oppo is neutral and clear, yet the Soul in comparison makes the Oppo sound just a touch veiled. Excellent recordings of piano and acoustic instrument ensembles take on greater clarity and slightly more pure voicing.
• Treble: the Oppo is extended and linear, yet the Soul is just a bit smoother and more natural, making the Oppo in comparison sound like it has a hint of grain.

I'm not a big fan of DSP, which is too often used as a gimmick. But I have come to use the Soul's DSP features under certain conditions.

• Tone controls: anyone with a big enough music library inevitably has poor quality recordings. The problem is often unbalanced frequency response, in which case the Soul's tone controls can improve things. Implemented in DSP, I find them more transparent than conventional analog tone controls.
• Headphone crossfeed: the Soul has Meier's crossfeed, which narrows L-R separation and is useful when listening on headphones to recordings having artificial hard L-R separation. It has 5 levels from subtle to obvious.
• Speaker crossfeed: the Soul has a separate function to widen L-R separation for speakers, with adjustable levels to tune for different speaker distances & angles.
• Headphone notch filter: many headphones have a narrow response peak. The Soul has an adjustable notch filter to tame these headphones. The filter is always -6 dB, Q=2, and the knob adjusts the frequency between 6 and 11 kHz. This is particularly effective with the HD-800.
• Digital filter: the Soul has a switch to select the standard "sharp" (linear phase) versus "slow" (minimum phase) digital filter.
• Redbook emphasis: the Soul implements this and provides a manual override. This is more of a historical curiosity since this obscure feature of the CD Redbook was so rarely used. But if you have old CDs from the 80s or 90s that used it, it's nice to have.

The Soul has excellent build quality, among the top tier in consumer & professional audio. It also has excellent support from Jan Meier, who stands behind his products and is willing to customize some aspects to suit individuals.

The Soul has some unusual engineering features that contribute to its excellent sound quality:

• Volume control is a 64-step switched attenuator in the analog gain-feedback loop. When you turn down the volume it reduces the gain rather than attenuating a fixed gain ratio. This reduces noise and distortion, especially at the low to medium volumes we actually use when listening.
• Switched power supplies - providing dead flat quiet stable DC to all internal components (digital and analog) without even a hint of 50/60 Hz ripple.
• Frequency shaped feedback (FF), which "unloads" both digital and analog gain stages for cleaner more transparent sound.
• The Soul uses dual DAC chips (Wolfson WM8741), one per channel (L and R), each in mono mode, in which this chip has slightly better performance.

The net effect of these engineering features makes the Soul the quietest (lowest noise) DAC or preamp I have heard or measured, especially at the low to medium volumes we actually use for listening. That lower noise contributes to absolute black musical background at all volume levels, accentuating low level subtle detail and transparency.

Now the Soul has some limitations:

• Balanced only: no unbalanced inputs or outputs.
• PCM only: no DSD. And sampling rates are limited to 32, 44, 48, 88.2, 96 and 192 kHz. No 176.4 or frequencies above 192k.
• Analog output is max 8 Vrms for a full scale 0 dB digital signal. It has a gain switch, but it's digital so using high gain (+6 dB) risks digital clipping. It would be nice to have an analog high/low gain switch like Meier has in his other amps. This could match the output to a wider range of headphones, or to boost analog gain if you have DSP in front of the Soul attenuating the digital signal (for example, digital parametric EQ).
• Appearance: the Soul looks and feels something like military signal processing equipment. Its build and part quality is impeccable, but no fancy displays, swanky enclosures or knobs. I enjoy this "black box" look and feel, but others might not, especially at this price point.

The Soul is the most transparent DAC and preamp that I have heard. It gets me closer to the music, making listening sessions more engaging. As an engineer, I like the non-nonsense industrial build quality that says "tools, not toys". I don't think more transparent, higher fidelity is possible at any price. For sound quality alone I would give it 5 stars (6, if I could!). But to be a realist I have to take it down 1/2 star due some of its limitations, which mean it won't be for everyone, and at its high price the field is wide open with so many other options to explore.