SOTA Pyxi Phono Stage Review

[amirm]

What remains is to investigate the goal of the development and that requires user feedback on the sound.

If I went by that, I would have had to give a negative rating to the product.... Do you really believe this with all that can go wrong in such "feedback?"

 

[amirm]

This is not a vanity project, nor a means to obtain financial benefit, but an act of curiosity, if you will- an attempt to close the gap between measurements and experience.

I don't see how you do that with every person using a different cartridge, audio system, etc. There is nothing there to control the variables. FYI, every product I test that gets negative reviews is countered with "but my listeners love it so you must be wrong." Heck, even things that don't make one iota of difference in the output of the audio device have such testimonials.

You did something great with creating an extremely accurate RIAA equalization curve. Don't drag that down with such claims, please.

Having said that, they choose to demonstrate their turntables at audio shows and audio society meetings/demos with the production Pyxi and the Acrux prototype, they have been extremely pleased with the comparative listening sessions, and these days when they send their new/updated TTs out for review they send a Pyxi along for the ride...

So say every one of your competitors.

 

[restorer-john]

You did something great with creating an extremely accurate RIAA equalization curve.

Absolutely.

 

[pma]

I wonder how well some of the built in HPFs work? A 4th order Butterworth with an Fc of 18Hz will only have 21dB of attenuation at 10Hz; I really think you need 6th order or higher to reduce woofer flapping without adversely affecting the first octave of the audio band.

Even the simplest, -6dB/oct HP C-R filter, behind the phono preamp, does the job in the area <=10Hz, reducing considerably the unwanted area, with negligible effect in the audio band. Yes it has to be followed by the opamp buffer.

 

[restorer-john]

Even the simplest, -6dB/oct HP C-R filter, behind the phono preamp, does the job in the area <=10Hz, reducing considerably the unwanted area, with negligible effect in the audio band. Yes it has to be followed by the opamp buffer.

View attachment 290177

Plenty of preamplifiers and integrateds use a switched -6dB/oct HPF using a simple RC. Works perfectly well.

 

[Muddywaters]

@wynpalmer congrats on the excellent, healthy birth” of your commercialized baby. Appreciate you sharing the details of the concepts behind it too. I’ve followed the development process elsewhere and you graciously shared the early white paper with me roughly 9 months ago. If my home hadn’t been wiped clean by Hurricane Ian storm surge I may have sampled the traveling show piece although I’m more interested in the balanced version potentially down the road to recovery.

I’m a bit perplexed by your desire for “subjective” input for validation to you. The usual omg “I built this and it’s the greatest thing since sliced bread”, yada yada, “timing putting any other phonostages in the dust”, paraphrasing some of the typical babble surfacing. With the recording capabilities of your RME I think you missed an opportunity to gather empirically the actual comparisons you participated in with a variety of phono pre’s. I’d be all over checking out recordings that could have been made during the “bake offs”. Considering the rigor you’ve dedicated in developing the product just seems a lost opportunity. Having an easy peasy method to compare would have been wonderful.

Kudos

 

[pma]

Considering the rigor you’ve dedicated in developing the product just seems a lost opportunity.

It might be only the marketing part of his whole story, probably considered necessary. I would bet for it. We all know the the “wow feedback“ effect and sometimes it may have a bit seductive effect. It is difficult to resist.

 

[wynpalmer]

@wynpalmer congrats on the excellent, healthy birth” of your commercialized baby. Appreciate you sharing the details of the concepts behind it too. I’ve followed the development process elsewhere and you graciously shared the early white paper with me roughly 9 months ago. If my home hadn’t been wiped clean by Hurricane Ian storm surge I may have sampled the traveling show piece although I’m more interested in the balanced version potentially down the road to recovery.

I’m a bit perplexed by your desire for “subjective” input for validation to you. The usual omg “I built this and it’s the greatest thing since sliced bread”, yada yada, “timing putting any other phonostages in the dust”, paraphrasing some of the typical babble surfacing. With the recording capabilities of your RME I think you missed an opportunity to gather empirically the actual comparisons you participated in with a variety of phono pre’s. I’d be all over checking out recordings that could have been made during the “bake offs”. Considering the rigor you’ve dedicated in developing the product just seems a lost opportunity. Having an easy peasy method to compare would have been wonderful.

Kudos

To add context.
Part of the way I started down this path was I was using the RME box to digitize various LPs. I followed the same strict procedure as is my wont and normalized all the recordings to 1dB below FS. This was in the early days of the DIY stage development- three or four years ago if I remember correctly. I digitized the outputs from a Hovland HP100 line, the Hovland HP100 tape monitor and the first rather simplistic DIY units and listened, and I noticed something strange- I felt sure that they sounded differently, so much sure that I developed clear preferences for one "source" versus the others depending on the musical genre/recording. This was curious I thought. I invited my youngest daughter, wife and friends, to participate in listening sessions and sent out a number of digitized recordings which were not identified by source to several interested parties- including a UK audio reviewer that I've been friends with since just post undergraduate days- he is a Physicist by training and spent time at the BBC and with me working on military electronics systems. (He's also, incidentally, a Fellow of the IEEE in the UK, just to provide some additional background). There were several recordings of a set of a number of tracks, I can't remember how many, produced using the three sources, and also with the twist of stepping the peak amplitude by +/-0.5dB amongst otherwise identical samples.
The results were extremely surprising. Although the samples were small, once the results were reported to me there were clear and consistent preferences.
I looked at the issue more closely. I thought, why would the two Hovland outputs sound so different, for example, and started measuring. What I found was that both the frequency response and the distortion levels were changed in the line output driver. The use of a low bias current JFET and tantalum bead in series, with even the 9k input impedance of the RME box and the c. 1m cables was sufficient to greatly increase the even order distortion and alter the frequency response at both ends of the spectrum.
I had my daughter conduct a double blind test- although a single blind would have been just fine as she doesn't care at all about such things- and my wife and I were able to pick out which source was which at a statistically significant rate, even if the number of recordings and sample size was small.
I then started to focus on the extant psychoacoustic literature, noting the evolution from the earliest finding as to the high relative sensitivity to high order distortion products to the present level of understanding where the frequency response is binned into overlapping spectral regions and both temporal and frequency response distortions are considered to be important, and tried to come up with a set of design criteria that satisfied those metrics, a set of criteria that could be readily implemented, and more importantly, measured, to enable a proxy to be created. I noted, with some wry humor, Bruno Pudzeys' rather apropos commentary on the use of feedback and the audiophile aversion to its use and the use of SMPS and opamps and went from there.
This led to the evolution of the earliest DIY designs, and the increasing complexity and functionality of them.
Friends and family who heard/borrowed/built the DIY units seemed to like them and discarded/replaced quite a number of both cheap and expensive phono stages, and the boards and build instructions were made available on AK and briefly DIY audio.
All I asked was that people report their listening experiences, good or bad, to me, and if possible, some details as to their experience. Many of these reports were as PMs or personal emails.
Incidentally, there have only been two "bad" reports of the sound of the units- and one of them was my UK reviewer friend who, rather humorously, was one that "failed" the recordings test by consistently simply choosing the loudest tracks. The second was a dealer in Colorado. Both love the "tube sound", whatever that is.
In any case, I digress.
The point is- I'm interested in this. I'm not doing this "research" with the benefits of a university grant, or infrastructure, nor do I wish to publish a serious technical paper on the subject.
A similar scenario exists concerning the warp filter. I have essentially replicated Alex Korf's work to the best of my ability, and the warp filter was implemented precisely to deal with the warp modulation that Shure's "paper" identified. It was originally designed in conjunction with listening sessions to determine the transparency, the cut-off being set in that way, then the complexity was increased to improve the rejection and the channel separation while retaining the same apparent audible transparency, and I've used it during recordings and also as a post-processing step with the DAC outputs to see if it is audible and effective simultaneously. The answer is no, and yes.

Getting feedback necessarily relies on the self-reporting of the "subjects", which I know is justifiably frowned upon, but it's the only realistic path forward that I have.
SoTa approached me, not I them, to do this, and I did so with considerable initial reluctance, but then thought what the heck, why not. The DIY effort was petering out. Few people actually seemed to be building the units, and fewer still were providing the input I was requesting. I refused remuneration, but was granted access to SoTas subjective test results, and things progressed from there.
In any case, I've moved on from this. I feel obliged to provide technical and "philosophical" support to the builds, but I no longer am actively accumulating experiences and I no longer have the test recordings for evaluations. I feel satisfied that with the necessarily limited scope and applicability of my attempts that the premise (that the design goals provide an audibly neutral source) have been satisfied.
Finally, I apologize for my apparent failure to live up to the purity of scientific endeavor that seemingly was expected of me.
Hey, I was just curious...

 

[anmpr1]

I’m a bit perplexed by your desire for “subjective” input for validation to you. The usual omg “I built this and it’s the greatest thing since sliced bread”, yada yada, “timing putting any other phonostages in the dust”, paraphrasing some of the typical babble surfacing.

If you live by the subjective review, you'll die by it; usually within a very short time. At least that has been my experience. In the heyday of analog subjectivity (as most might recall) all the magazines were into the MC of the Month club (along with associated and various step up devices). What was best in January, was superseded in February, and by April everything was totally forgotten, due to whatever was imported from Japan in March.

As far is this box? The designer should be happy with his product. It doesn't cost too much in the scheme of these things, and will satisfy prospective buyers, especially if they are honest with themselves about what they can and can't hear. If there are areas of improvement to be made, the next model can change from Pyxi to the Myxi.

Speaking of honest..., let's be. We know how no matter how good it sounds, it would all sound better with a Hegeman Input Probe in the signal path. Everyone knows that!

Like the old meme reminds us:

 

[Thomas_A]

Regarding the warp-induced noise, I reduced it by around 6 dB when I changed tonearm (Moerch UP4 4 g effective mass), and it would decrease further with the "anisotropic arm"; there would be no harm having higher resonance, 15-20 Hz, for vertical direction. Having mono-pre for bass <80-100 Hz will also cancel som noise to the amp/speakers.

 

[wynpalmer]

Regarding the warp-induced noise, I reduced it by around 6 dB when I changed tonearm (Moerch UP4 4 g effective mass), and it would decrease further with the "anisotropic arm"; there would be no harm having higher resonance, 15-20 Hz, for vertical direction. Having mono-pre for bass <80-100 Hz will also cancel som noise to the amp/speakers.

The warp filter does precisely what you suggest, but in an extremely controlled and non audible way. Please read the whitepaper that was introduced earlier.

 

[wynpalmer]

If you live by the subjective review, you'll die by it; usually within a very short time. At least that has been my experience. In the heyday of analog subjectivity (as most might recall) all the magazines were into the MC of the Month club (along with associated and various step up devices). What was best in January, was superseded in February, and by April everything was totally forgotten, due to whatever was imported from Japan in March.

As far is this box? The designer should be happy with his product. It doesn't cost too much in the scheme of these things, and will satisfy prospective buyers, especially if they are honest with themselves about what they can and can't hear. If there are areas of improvement to be made, the next model can change from Pyxi to the Myxi.

Speaking of honest..., let's be. We know how no matter how good it sounds, it would all sound better with a Hegeman Input Probe in the signal path. Everyone knows that!

Like the old meme reminds us:


View attachment 290633

The next model has already been designed. In fact two different models- a MM only unit (PyxiMM?) with switchable 35/45dB gains and MOSFET inputs, the Acrux with, well, pretty well everything better (distortion, noise, power supply rejection etc.) and true MM/MC separate channels and 2dB gain steps over a 10dB range, balanced outputs, more input loading options, and the very sophisticated warp filter.
It's all fun...

 

[ronniebear]

40 years ago, Nakamichi offered an elegant and low-cost solution to the issue of extreme subsonic frequency information: a simple high-pass filter plug in called the Nakamichi SF-10. It sold for about $10 in the early 1980s. You plugged the turntable RCA cables into the SF-10 filter, then the filter into the phono stage. It was built to an exceptionally high standard and provided at least 12 db/octave rolloff below 20 hz in a manner which did not interfere with phase relationships of audible frequencies. You can find the Nakamichi SF-10 listed in the accessories of the various Audio/Stereo Review/High Fidelity annual equipment directories from that era.

A company which presumably bought the Nakamichi brand is peddling plugs and connectors on Amazon, but NOT anything like the vintage SF-10 subsonic filter.
Amazon shows one company called Harrison Labs offering an "FMOD Inline Rumble Subsonic Filter Crossover Pr 30Hz High Pass RCA". Perhaps somebody here who is a vinyl aficionado would like to buy it and run it through objective testing?

 

[Thomas_A]

The warp filter does precisely what you suggest, but in an extremely controlled and non audible way. Please read the whitepaper that was introduced earlier.

Once I was thinking of getting a similar filter but since I use two subs in mono (crossover 100 Hz) I am not sure what the benefit would be. Both the power amp and drivers gets less of the warp LF noise. I also got about 6 dB less of it changing tonearm.

Tonearm mass and noise LP playback.pdf

Shared with Dropbox

www.dropbox.com

 

[cgallery]

40 years ago, Nakamichi offered an elegant and low-cost solution to the issue of extreme subsonic frequency information: a simple high-pass filter plug in called the Nakamichi SF-10. It sold for about $10 in the early 1980s. You plugged the turntable RCA cables into the SF-10 filter, then the filter into the phono stage. It was built to an exceptionally high standard and provided at least 12 db/octave rolloff below 20 hz in a manner which did not interfere with phase relationships of audible frequencies. You can find the Nakamichi SF-10 listed in the accessories of the various Audio/Stereo Review/High Fidelity annual equipment directories from that era.

A company which presumably bought the Nakamichi brand is peddling plugs and connectors on Amazon, but NOT anything like the vintage SF-10 subsonic filter.
Amazon shows one company called Harrison Labs offering an "FMOD Inline Rumble Subsonic Filter Crossover Pr 30Hz High Pass RCA". Perhaps somebody here who is a vinyl aficionado would like to buy it and run it through objective testing?

The resulting f3 from those sorts of devices can vary quite a bit depending on the input impedance of the device to which they're connected.

 

[wynpalmer]

Once I was thinking of getting a similar filter but since I use two subs in mono (crossover 100 Hz) I am not sure what the benefit would be. Both the power amp and drivers gets less of the warp LF noise. I also got about 6 dB less of it changing tonearm.

Tonearm mass and noise LP playback.pdf

Shared with Dropbox

www.dropbox.com

Not exactly the same thing. Your approach sums the LF mono and stereo signals to produce a composite mono signal and applies that to both channels.
i.e.
2LOUTLP=2ROUTLP = LINLP+RINLP.
The warp approach does not sum the two channels but takes the ordered low pass difference of the two channels and subtracts that from the appropriate channel.
i.e
2LOUT= 2LIN-(LINLP-RINLP) = 2LIN+RINLP-LINLP
2ROUT= 2RIN-(RINLP-LINLP) =2RIN+LINLP-RINLP
The stage also does this using a higher order filter characteristic that improves the LF cutoff characteristic.
This allows the stage to have higher channel separation at 1kHz and above and also have a controlled stereo magnitude response with a small (c. 0.3dB p-p) ripple in the stereo passband rather than a single order asymptotic response, which improves the "audible neutrality" of the characteristic in the critical upper bass/lower midrange region, while retaining about 45dB of attenuation at the fundamental warp frequency.
My apologies if I am poorly explaining this distinction.

 

[wynpalmer]

If you live by the subjective review, you'll die by it; usually within a very short time. At least that has been my experience. In the heyday of analog subjectivity (as most might recall) all the magazines were into the MC of the Month club (along with associated and various step up devices). What was best in January, was superseded in February, and by April everything was totally forgotten, due to whatever was imported from Japan in March.

As far is this box? The designer should be happy with his product. It doesn't cost too much in the scheme of these things, and will satisfy prospective buyers, especially if they are honest with themselves about what they can and can't hear. If there are areas of improvement to be made, the next model can change from Pyxi to the Myxi.

Speaking of honest..., let's be. We know how no matter how good it sounds, it would all sound better with a Hegeman Input Probe in the signal path. Everyone knows that!

Like the old meme reminds us:


View attachment 290633

Well, the idea was to produce a technically excellent design, using the anti-audiophile design approaches that were originally posited. The specific goals were an extremely compliant RIAA response and extremely low HF distortion, below -110dBc at the units rated output, and excellent, indeed near perfect, many tone distortion characteristics using my preferred test methodology.
This goal did not explicitly depend on subjective responses, but hopefully would result in a subjectively excellent outcome (with certain caveats).
There is absolutely no live or die in this as far as I'm concerned but having all of my audio buddies (with one exception) now use the design in preference to many cheaper and a number of much, much more expensive units, is quite pleasing, I must admit.
I've always made a point to declare in any postings that the design has the characteristics it has, but that any subjective outcomes (i.e. whether the user likes it or not) are entirely up to the listener, but being present as an observer in many listening sessions, especially as the undeclared "father" of the design, and noting the reactions, has been interesting to say the least, as many declare that they hear exactly what I believe I hear, without my opinion or bias being presented. It's like an anonymous composer being introduced to the audience after his piece has been performed. Yeah, this sounds ridiculous and pompous, and was made so deliberately, but I'm sure that you get the point.
As I wrote, it's all fun, and this too shall pass.

 

[krichard2496]

Well, the idea was to produce a technically excellent design, using the anti-audiophile design approaches that were originally posited. The specific goals were an extremely compliant RIAA response and extremely low HF distortion, below -110dBc at the units rated output, and excellent, indeed near perfect, many tone distortion characteristics using my preferred test methodology.
This goal did not explicitly depend on subjective responses, but hopefully would result in a subjectively excellent outcome (with certain caveats).
There is absolutely no live or die in this as far as I'm concerned but having all of my audio buddies (with one exception) now use the design in preference to many cheaper and a number of much, much more expensive units, is quite pleasing, I must admit.
I've always made a point to declare in any postings that the design has the characteristics it has, but that any subjective outcomes (i.e. whether the user likes it or not) are entirely up to the listener, but being present as an observer in many listening sessions, especially as the undeclared "father" of the design, and noting the reactions, has been interesting to say the least, as many declare that they hear exactly what I believe I hear, without my opinion or bias being presented. It's like an anonymous composer being introduced to the audience after his piece has been performed. Yeah, this sounds ridiculous and pompous, and was made so deliberately, but I'm sure that you get the point.
As I wrote, it's all fun, and this too shall pass.

Translation of 11 pages: "Yeah I know the Radio Manufacturers Association was recommending weighted THD tests in 1937, and Shorter was demanding them in 1949, but we do science here in 2023. That AX? It's an expensive box, it says "floating".... none of our real readers actually use these things to listen to records anyway... Besides soldering two or three resistors together to form a resistive L-pad to break a pretty bad ground loop sounds like a lot of trouble."

You send us one of yours, we'll send you one of ours, and we will both have a hearty laugh.

 

[wynpalmer]

I have an ex-associate at ADI who sent me a link to an article on ADI "seismic sensors", having read the Pyxi review.
I think it is of interest. Perhaps others agree, in particular the section on "geophones".

https://www.analog.com/en/analog-dialogue/articles/understanding-the-fundamentals-of-earthquake-signal-sensing-networks.html

 

[jjmanda]

I bought one of these Pyxi's and it has a terrible ground loop issue that I can't get rid of.

A direct swap with a Pro-Ject S3B I have in comparison has no issues.

I sent SOTA an email and waiting on their response. If I can't fix it, I'll be sending it back.