SOTA Pyxi Phono Stage Review

[wynpalmer]

Clipping and overload margin is a bigger issue in digital domain than in an analog circuit.

The RME box flags any clips and the design handles any intersample issues flawlessly. Any DSP correction (Anthem) I use also does not, I believe, experience any overload margin issues, at least none that I've detected, and can be, and is, turned off for comparison purposes.

 

[Bob from Florida]

Unfortunately the explanation as to why a subsonic filter is needed completely neglects the fact it is necessary because of the way cartridges work, as usual these days.
It seems almost everybody doesn't know.

It isn't because records aren't flat or because record players have rumble, it is because all the output of a cartridge below around 2x the natural frequency of the "stator" on its suspension is exaggerated in amplitude and wrong in phase by the nature of the device since the "stator" part of the transducer isn't yet a stationary relative to the LP. At around 2x this natural frequency the headshell becomes a reasonable approximation to an actual stator - remaining reasonable dynamically stationary relative to the LP.
Below that frequency the output of the cartridge is spurious rubbish and should be removed, however flat and concentric the LP or quiet the turntable.

I am astonished at the lack of knowledge about this in the record player enthusiast cohort these days. It is absolutely basic and was well known in the 60's and 70's when I was first interested and then involved.

The need for a high pass filter cut off is entirely to do with the physics of how a cartidge works and nothing whatsoever to do with the LP itself or record player rumble. It is just transducer basics.

Frank,

I just put Bob James Expresso LP on my table - Clearaudio Performance DC - has the ceramic magnetic bearing that "floats" the platter. Tonearm is Satisfy Carbon - 7 grams mass. Cartridge is Hana SL medium compliance and weighs 5 grams. Clearaudio 12 ounce Concept center weight on spindle- keeps the record from slipping if using a cleaning brush. That is the setup - record is "ruler" flat. No visible woofer movement that I can discern. No disrespect intended - how is this possible with regards to the commentary on physics of the playback medium?

 

[cgallery]

Frank,

I just put Bob James Expresso LP on my table - Clearaudio Performance DC - has the ceramic magnetic bearing that "floats" the platter. Tonearm is Satisfy Carbon - 7 grams mass. Cartridge is Hana SL medium compliance and weighs 5 grams. Clearaudio 12 ounce Concept center weight on spindle- keeps the record from slipping if using a cleaning brush. That is the setup - record is "ruler" flat. No visible woofer movement that I can discern. No disrespect intended - how is this possible with regards to the commentary on physics of the playback medium?

What sort of speakers/subs are we talking? Woofers in sealed cabinets pump a lot less.

 

[Bob from Florida]

What sort of speakers/subs are we talking? Woofers in sealed cabinets pump a lot less.

Reference 3A Grand Veenas - 2 - 8 inch woofers per speaker. Sub is a SVS 3000 Micro.

 

[pma]

how is this possible with regards to the commentary on physics of the playback medium?

You may have well centred disc, with good surface flatness, your phono pre may have HP filter, or your power amp may have -3dB LF corner quite high.

 

[Bob from Florida]

You may have well centred disc, with good surface flatness, your phono pre may have HP filter, or your power amp may have -3dB LF corner quite high.

ifi Zen phono with filter off. Luxman 507 ux 2 integrated - straight option selected bypassing tone controls.

 

[wynpalmer]

You have to "excite" the modes for them to appear, and depending on the design of the PU they can be quite well damped, and I do not believe that they are necessarily harmonically related to the platter rotation frequency so they tend to be somewhat chaotic, but I'm by no means an expert in these matters.
However, in my opinion this is a problem that has far more theoretical consequences than actual (there's that empirical evidence thread again), so I'm bowing out.

 

[morillon]

I have a different approach. I know the cartridge sensitivity at 1kHz, 5cm/sec and as a result I know the max output of the cartridge (at most 14dB above sensitivity) based on multiple inputs (Shure and other evaluations, my own history of digitization). I also know the gain of the phono stage at 1kHz- which is extremely well controlled- and the RIAA characteristic is essentially perfect, so I know the max output.
The ADC has a much better dynamic range than the LP playback system, so I digitize at 96kHz, 24 bits, to allow for normalization, add a few dBs to the expected max output, select the ADC input FS, and adjust the gain using the ADC or the phono stage gain set capability, then let it rip. This is exactly the same for all vinyl.
I then do a software clean on the file to remove unwanted noise/ticks/scratches- being careful to not audibly degrade the "audiophile" aspects of the source and renormalize to a peak level of 1dB below FS, which occurs at the 96k 32 bit level, I then save the FLAC file.
For example, with the Miyajima Madake and the Acrux.
Madake sensitivity - 230uv rms @1kHz, 5cm/sec. or c. -73dBv. The manufacturers reported and actual sensitivities actually more or less agree.
Max possible output is thus -73+14= -59dBv. The gain of the Acrux is 70dB, so the result is +11dBv.
One of the ADC settings is +19dBu FS rms for a sinusoidal input, and I have verified that this is indeed the case within a few tenths of a dB, which is +16.8dBv. I then add 2dB to the channel gain of the Acrux, to produce +13dBv max at the input, and digitize. This should provide at least 3dB of margin.
Works perfectly every time with no clipping except on the extremely rare (thank goodness) occasions when I drop the arm.

I was just pointing to a very factual approach... and "easy" to quickly adjust the input, an adc...
the data manufacturers of the cartdriges tonarms ,are not always so reliable etc. and sometimes, limits the "mathematical" models..


;-)

 

[pma]

However, in my opinion this is a problem that has far more theoretical consequences than actual (there's that empirical evidence thread again), so I'm bowing out.

theoretical consequences ......

I normally prefer to give hints only - but - if an explanation is needed, here it goes: it is a record from phono preamp output, the turntable is playing Elton John record that has poor geometrical flatness, 33 1/3 rpm revs excitate tonearm+cartridge resonance at 9Hz that is always the highest amplitude in the spectrum and can be seen very well in the time record. The phone pre without HP filter has no chance to cut it. So these are those "theoretical consequences" .

 

[morillon]

You have to "excite" the modes for them to appear, and depending on the design of the PU they can be quite well damped, and I do not believe that they are necessarily harmonically related to the platter rotation frequency so they tend to be somewhat chaotic, but I'm by no means an expert in these matters.
However, in my opinion this is a problem that has far more theoretical consequences than actual (there's that empirical evidence thread again), so I'm bowing out.

maybe if one day a revision of the pyxi does this, it will just be possible to remove the largest capacitance adjustment and replace it with an subsonic filter in on off
(will be more useful..that's for sure)
;-)

 

[pma]

it is a record from phono preamp output, the turntable is playing Elton John record that has poor geometrical flatness,

Typical "audio" spectrum from the vinyl rip of that record

Who wants and needs that near 10Hz resonance area? 20g effective mass, 20um/mN compliance, fits quite well to system resonance. HP filter like 2-4th order tuned at 20-30Hz will help. It is sometimes a problem with "highend" audio designers that they do not design according to facts, but rather according to their eternal circuit visions.

 

[Bob from Florida]

theoretical consequences ......



View attachment 289719

I normally prefer to give hints only - but - if an explanation is needed, here it goes: it is a record from phono preamp output, the turntable is playing Elton John record that has poor geometrical flatness, 33 1/3 rpm revs excitate tonearm+cartridge resonance at 9Hz that is always the highest amplitude in the spectrum and can be seen very well in the time record. The phone pre without HP filter has no chance to cut it. So these are those "theoretical consequences" .

View attachment 289720 View attachment 289721 View attachment 289722 View attachment 289724

If I understand you correctly - excitation must occur to generate the resonance that results in the excessive woofer cone movement. This is what I previously understood. Below from Frank's post is where things became confusing - at least for me.

"It isn't because records aren't flat or because record players have rumble, it is because all the output of a cartridge below around 2x the natural frequency of the "stator" on its suspension is exaggerated in amplitude and wrong in phase by the nature of the device since the "stator" part of the transducer isn't yet a stationary relative to the LP. At around 2x this natural frequency the headshell becomes a reasonable approximation to an actual stator - remaining reasonable dynamically stationary relative to the LP.
Below that frequency the output of the cartridge is spurious rubbish and should be removed, however flat and concentric the LP or quiet the turntable."

I am fairly certain Frank "knows his stuff" and this is likely just a communication issue, ie lack of understanding on my part.

 

[pma]

If I understand you correctly - excitation must occur to generate the resonance that results in the excessive woofer cone movement. This is what I previously understood.

Yes, the excitation must occur to get the electrical output as a result of mechanical resonance of the effective mass (tonearm + cartridge + screws) and cartridge compliance. In my case 20g and 20um/mN, calculated resonance frequency is 7.96Hz, measured 8.75Hz.


This is in quite perfect correspondence.

Unfortunately, due to always existing record mechanical imperfections, the resonance excitation is always present, with different amplitude. The better the record, the less it is pronounced. Anyway, it is always unwanted and as the amplitude is unpredictable, it is better to cut the useless frequencies than to risk a potential issue.

I am fairly certain Frank "knows his stuff" and this is likely just a communication issue, ie lack of understanding on my part.

He does, definitely. He is basically a mechanical engineer, I am an electrical engineer, so we may use a bit different technical language. However, the physics is just one, and so is the understanding of the physics phenomena.

 

[Frank Dernie]

The response of the cartridge/arm/headshell to the mechanical excitations present have nothing to do with whether the playback electronics have a high pass or not.
We could argue whether this is entirely true or not- for example does a lower load impedance on the cartridge cause the effective mechanical stiffness of the cantilever to increase, as some have suggested, but that's clearly not in play here.
What is in play is whether the infrasonic modes (which, I believe, if present and randomly excited, should actually present themselves in a chaotic way) are sufficiently "audible" to cause listeners to interpret them as extra warmth or something similar- presumably by either some intermodulation or the creation of a background acoustic ambient LF "field" so to speak.
Again, I can only refer to the experiences of myself and many others. This is not what is heard. If anything, the opposite is true. The bass sounds less "muddy", the acoustic "field" is more differentiated. It's in fact, very digital like in some sense, with some of the analog character that people like, added.
What is generally audible is recorded rumble on some LPs and warps. Nothing else.
As it turns out, I have the ability to add LF HP filtering as well as warp filtering to my system, and to measure responses down to the mHz region, and one exercise I went through was to place the arm/cartridge on a stationary platter, with the motor running and the belt removed to explore the mechanical system noise and resonances and the interaction between the speakers (excited by the DAC output) and the cartridge. (As an aside, this was originally done to demonstrate to the manufacturer of the TT I have that it had certain problems, which took two trips back for them to fix as they didn't have a way to measure the problems!) It might be interesting to resurrect that test, or something similar, although the whole thing is becoming severely off topic and probably should just end, now.

It is the mechanical transducer I am (very) familiar with, not the electronics (at all) the reality is that simple dynamics (very basic) means that all the output from a pickup cartridge below ~2x the natural frequency of the mass on the compliance is sufficiently inaccurate to be considered spurious.
On that basis I would say it is good engineering practice to remove it if possible. I am not qualified to say how feasible this is.

I would expect the sub sonic output, if any, to perhaps give the impression of a big space, we found many years ago adding a bit of noise increases the impression of stereo image size particularly depth but that is an artifact, not sound reproduction.

The problem is that even if there is some sub-sonic information recorded on the disc a traditional cartridge/arm is physically incapable of accurately reproducing it. This is all the simple physics of the dynamic system and whilst damping shifts both amplitude and the frequency at which the headshell becomes an acceptable approximation to stationary wrt the record these are small effects, not fundamental.

 

[Frank Dernie]

Frank,

I just put Bob James Expresso LP on my table - Clearaudio Performance DC - has the ceramic magnetic bearing that "floats" the platter. Tonearm is Satisfy Carbon - 7 grams mass. Cartridge is Hana SL medium compliance and weighs 5 grams. Clearaudio 12 ounce Concept center weight on spindle- keeps the record from slipping if using a cleaning brush. That is the setup - record is "ruler" flat. No visible woofer movement that I can discern. No disrespect intended - how is this possible with regards to the commentary on physics of the playback medium?

I am just talking about good engineering practice, or my view of it.
Since it is a fact that the output of the cartridge is inaccurate enough to be spurious below 2x the natural frequency I would call it good practice to filter it out.

OTOH, obviously if there is no excitation at those frequencies there is no output so nothing to filter out, but there often will be in most real world playing of an LP.

 

[wynpalmer]

The Pyxi will not be altered to include a subsonic filter. SoTa does not want it. Users do not want it or need it- or at least none that have communicated to them or me, and ultimately that is all that matters. The user group that has reported on the design in its various incarnations vastly exceeds the number that have declared that the unit is unacceptable because of this function that was deliberately left out.
You certainly understand that the physical process that you describe- the resonance peaking for the arm- is well known and most users will set up their arms/cartridges to at least have some knowledge or "optimization" of this phenomenon, so it's not like this is some miraculous revelation.
The discussion has evolved from "it's always there it doesn't need to be excited" (it does) to "I have this LP that is poor and it does it" which is actually quite reasonable, just largely inconsequential- or at least in my mind and the mind of many others.
If I have an occasional LP that exhibits this issue, I can do one of three things. I can use the warp function that works extremely well on, well, warps- i.e. erroneously vertically modulated signals, or the HP (rumble) filter on the preamp, or just ignore the motion of the woofers, if I can see it. This is not an unusual situation.
This is my last word on the situation. I'll end my monitoring of this thread. Please continue with the flagellation until you grow tired.

 

[wynpalmer]

Actually I lied. I just want to post one more thing, not my commentary, but one from AK, and not specifically on the the Pyxi, but the Pyxi DIY precursor. This comment is from a music prof. at a university in in Sweden. Both he and his wife are "failed" musicians. He also does some turntable related "stuff" for select clients. His comment about ASR is unfortunate and I do not concur, so please ignore it, but I nevertheless value his commentary as his subjective analysis and opinions have been very valuable over the years. "I've stayed out of this discussion so far, since I don't have a Pyxi (not available in Europe, unfortunately). But I was one of the early builders of the DIY kit, in version 1, which spec-wise should be close to the Pyxi, so perhaps I could fill in something here As to listening, I don't count myself an audiophile, and I certainly give priority to what I hear before any specs. I self-identify as a failed musician, and use hifi gear to listen for what the musicians really are doing. This means more or less that I don't give a rat's ass about the standard audiophile stuff, with warmth, depth of sound field, room placement and such. What I listen for is the sound of the instruments, the timing between the musicians, the phrasing and rhythmic details of the different parts, and such. If a gadget makes me and my wife with a better trained musical ear to jump at the same time listening to old recordings because we can hear background musicians syncopating in ways we haven't heard before, we know the gadget is worth listening to. I also keep these priorities when evaluating the turntables I restore, which folks buying them seem to appreciate. It is very seldom these priorities aren't also in sync with the normal audiophile things, but frankly, we don't care enough for those to let them take priority over the musical stuff. On the other hand, I've also been one of the folks harping on about Wyn's perspective on psychoacoustics and measurements. Not because I'm a specs fetichist - I mostly think Amir's work at ASR is crap. When I was a kid I made tables with specs over various hifi gear (yes, I was that nerdy), and attempted to weight the numbers in order to find the best ones, which I of course never could afford, or even listen to. In my view, what Amir is doing is precisely the same thing, but only reducing the method to only consider harmonic distortion. And he is doing this in 2023, totally disregarding all of the psychoacoustic research done the last fifty years, showing that THD does not equate to the perceived sound quality of the DUT. As I see it Wyn's work is the most interesting use of all of that research I've come across. So, the DIY phono stage we use (switchable between MM and MC) is to our ears stunningly good. Interestingly, we also get the same reactions from guests and customers listening to it. It is quiet, without any audible hum or noise at any reasonable output levels. It does timing and dynamics that leaves any other phono stage we've heard in the dust. It is neutral in the best possible way - contrary to your opinion, I think the 0.1 dB stuff really matters, by keeping the phono stage out of the way for how the recording was actually meant to sound. So, my recommendation is to ignore the specs Wyn must focus on in order to be able to get his design to do what he wants it to. Listen to the damn thing, and report back what you have heard. Wyn knows what he has measured, what he needs now is folks reporting what they hear, since that is the next step in testing the psychoacoustic theory the work is based on. If everybody loves it, that is nice and good, but even more interesting would be to identify possible common audible anomalies between what folks hear and the theory. " His last paragraph encapsulates why I did this. User feedback is ALL I care about. Understand that I have the technical ability to add ANY of the various capabilities that have been mentioned. You don't get to be an ADI Fellow or even rarer, Senior Fellow (only Barrie Gilbert and Paul Brokaw had "made it" before me) because you're an idiot.

 

[pma]

The Pyxi will not be altered to include a subsonic filter. SoTa does not want it. Users do not want it or need it- or at least none that have communicated to them or me, and ultimately that is all that matters. The user group that has reported on the design in its various incarnations vastly exceeds the number that have declared that the unit is unacceptable because of this function that was deliberately left out.

You are certainly not forced to include a subsonic filter. We were just discussing what is technically correct and what is not. That's all. The rest is the marketing, which is not much interesting in the forum based on evidence, like ASR is.

 

[Frank Dernie]

You certainly understand that the physical process that you describe- the resonance peaking for the arm- is well known and most users will set up their arms/cartridges to at least have some knowledge or "optimization" of this phenomenon

Most users know they need to get the resonance frequency in the right area, which is true.
What pretty well no enthusiasts seems to understand, as far as I can tell reading what is written nowadays, is that the output from this sort of sensor is inaccurate rubbish below 2x Fn.

I don’t care at all whether your device ever gets a filter, I am not in the market for one .

I am simply exasperated that here we are in 2023 and enthusiasts are ignorant about the mechanical side of record players which were well known and understood 70 years ago, often the most ardent disciples. There is a lack of understanding of the mechanical aspects of seismic transducers in the hifi press and forums - which is so common as to be pretty well ubiquitous.

Anyway, I’m out of here, I have 4 record players loads of RIAA stages but currently use a device which digitises the cartridge output directly and applies the necessary filter and corrections in maths.

 

[Bob from Florida]

I have 4 record players loads of RIAA stages but currently use a device which digitises the cartridge output directly and applies the necessary filter and corrections in maths.

Frank - are you using the Puffin or something else? That does seem to be the most effective way to limit the bandwidth and apply accurate RIAA correction.