SOTA Pyxi Phono Stage Review

[amirm]

This is a review and detailed measurements of the Pyxi Phono Stage by SOTA. It is on kind loan from a member and costs US $300.

Well.... the design is not going to win any awards with LED, power and MM/MC selector not being aligned. Operationally it is fine and I appreciate the loading dip switches being in the back rather than buried inside or underneath:

The AC transformer is rated at 14 volt/500 ma and as these tend to do, it gets a bit warm.

I like the large grounding screw. Measurements you are about to see are my best attempt at lowering the mains hum. Your setup may vary.

I like that the company provides detailed specifications in the manual. Here are the MM measurements and conditions:

SOTA Pyxi Measurements
Let's start with our usual dashboard in MM mode:

I wish the spike at 180 Hz was not there as it indicates noise from the power supply. It dominates SINAD which is still good but could be better (SINAD was varying a few dBs):

So definitely competent. Company specs a "THD" number. Assuming it really means that, i.e. there is no noise component, here is my measurement of that:

Close enough. Noise spec is provided a-weighted with the same 10 mv input and that is right on the money:

Back to our dashboard, MC mode with 0.5mv input is naturally worse:

But again it is dominated by power supply noise.

Most important measurement is implementation of RIAA equalization and here, SOTA does a perfect job:

I don't think I have ever measured one this good or if I have, this is a good tie with it.

Unfortunately we don't have a lot of headroom:

As a result, pops and ticks are going to distort and sound even worse. We can sweep for other frequencies:

Interesting that at higher frequencies it doesn't clip right away but distortion gradually increases.

Switching back to purely THD measurement (no noise), we can see very low distortion in MM and almost as good in MC:

Conclusions
SOTA's design partners (Wyn Palmer and Bill of Phoenix Engineering) have done a superb job of implementing RIAA equalization which is the heart of any phono stage. Distortion is very low and near top of the chart as well. Accurate measurements are provided which is a delightful and rare thing to see in audio. The only issue is low headroom requiring clean LPs to play, or alternatively, lack of sensitivity to pops and ticks. I wish power supply noise was lower as that would then land it at the top of the chart.

I am going to recommend the SOTA Pyxi phono stage.

----------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

 

[abdo123]

Are you under the impression that a better power supply would improve the noise performance?

 

[amirm]

No. The external thing is just an AC transformer. The rectifier and filtering is inside and that is what needs improving. I understand they are working on a "lower noise" version so maybe that is what they are addressing.

 

[abdo123]

I'm not sure how i feel about the lack of rumble filters, my subwoofers are sealed so it shouldn't be a concern but if the 'stars align' it might cause some undesirable extra distortion, if they're working on a new revision i hope they consider a toggleable rumble filter in the next revision.

 

[amirm]

Ah yes, meant to comment on that and forgot.

 

[Koeitje]

Well, not really SOTA but its not bad.

 

[Hayabusa]

This is a review and detailed measurements of the Pyxi Phono Stage by SOTA. It is on kind loan from a member and costs US $300.
View attachment 288488
Well.... the design is not going to win any awards with LED, power and MM/MC selector not being aligned. Operationally it is fine and I appreciate the loading dip switches being in the back rather than buried inside or underneath:
View attachment 288489
The AC transformer is rated at 14 volt/500 ma and as these tend to do, it gets a bit warm.

I large the large grounding screw. Measurements you are about to see are my best attempt at lowering the mains hum. Your setup may vary.

I like that the company provides detailed specifications in the manual. Here are the MM measurements and conditions:
View attachment 288490

SOTA Pyxi Measurements
Let's start with our usual dashboard in MM mode:
View attachment 288491
I wish the spike at 180 Hz was not there as it indicates noise from the power supply. It dominates SINAD which is still good but could be better (SINAD was varying a few dBs):
View attachment 288492

So definitely competent. Company specs a "THD" number. Assuming it really means that, i.e. there is no noise component, here is my measurement of that:
View attachment 288493

Close enough. Noise spec is provided a-weighted with the same 10 mv input and that is right on the money:
View attachment 288494

Back to our dashboard, MC mode with 0.5mv input is naturally worse:
View attachment 288495

But again it is dominated by power supply noise.

Most important measurement is implementation of RIAA equalization and here, SOTA does a perfect job:
View attachment 288497
I don't think I have ever measured one this good or if I have, this is a good tie with it.

Unfortunately we don't have a lot of headroom:
View attachment 288498

As a result, pops and ticks are going to distort and sound even worse. We can sweep for other frequencies:
View attachment 288499
Interesting that at higher frequencies it doesn't clip right away but distortion gradually increases.

Switching back to purely THD measurement (no noise), we can see very low distortion in MM and almost as good in MC:
View attachment 288500

Conclusions
SOTA's design partners (Wyn Palmer and Bill of Phoenix Engineering) have done a superb job of implementing RIAA equalization which is the heart of any phono stage. Distortion is very low and near top of the chart as well. Accurate measurements are provided which is a delightful and rare thing to see in audio. The only issue is low headroom requiring clean LPs to play, or alternatively, lack of sensitivity to pops and ticks. I wish power supply noise was lower as that would then land it at the top of the chart.

I am going to recommend the SOTA Pyxi phono stage.

----------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

>>As a result, pops and ticks are going to distort and sound even worse

Do we have evidence that pop and ticks are reaching that level? 50mv is a 20dB headroom w.r.t. 5mv... looks like it should be enough?

 

[SIY]

Do we have evidence that pop and ticks are reaching that level? 50mv is a 20dB headroom w.r.t. 5mv... looks like it should be enough?

What's even more important is overload recovery time. If a click or pop clips the preamp but the preamp recovers instantaneously, no harm no foul. Morgan Jones shows some captured waveforms for record ticks in his book Valve Amplifiers, and 20dB is not unreasonably large.

Also a general note: the S/N of a cartridge just sitting there (i.e., not including turntable or surface noise) is maybe 70dB. So getting significantly better noise performance is not particularly important in this application.

 

[abdo123]

Also a general note: the S/N of a cartridge just sitting there (i.e., not including turntable or surface noise) is maybe 70dB.

a cartridge just sitting there does not close a circuit, so there would be no extra noise, that's what i measured at least.

 

[Bob from Florida]

I'm not sure how i feel about the lack of rumble filters, my subwoofers are sealed so it shouldn't be a concern but if the 'stars align' it might cause some undesirable extra distortion, if they're working on a new revision i hope they consider a toggleable rumble filter in the next revision.

I have that switch on my Zen Phono, but have never had a reason to activate the feature. None of my previous phono preamps had the option. Might be more useful with certain turntables or warped records - very few in my case.

 

[respice finem]

A name like SOTA is bold indeed...

 

[morillon]

This is a review and detailed measurements of the Pyxi Phono Stage by SOTA. It is on kind loan from a member and costs US $300.
View attachment 288488
Well.... the design is not going to win any awards with LED, power and MM/MC selector not being aligned. Operationally it is fine and I appreciate the loading dip switches being in the back rather than buried inside or underneath:
View attachment 288489
The AC transformer is rated at 14 volt/500 ma and as these tend to do, it gets a bit warm.

I large the large grounding screw. Measurements you are about to see are my best attempt at lowering the mains hum. Your setup may vary.

I like that the company provides detailed specifications in the manual. Here are the MM measurements and conditions:
View attachment 288490

SOTA Pyxi Measurements
Let's start with our usual dashboard in MM mode:
View attachment 288491
I wish the spike at 180 Hz was not there as it indicates noise from the power supply. It dominates SINAD which is still good but could be better (SINAD was varying a few dBs):
View attachment 288492

So definitely competent. Company specs a "THD" number. Assuming it really means that, i.e. there is no noise component, here is my measurement of that:
View attachment 288493

Close enough. Noise spec is provided a-weighted with the same 10 mv input and that is right on the money:
View attachment 288494

Back to our dashboard, MC mode with 0.5mv input is naturally worse:
View attachment 288495

But again it is dominated by power supply noise.

Most important measurement is implementation of RIAA equalization and here, SOTA does a perfect job:
View attachment 288497
I don't think I have ever measured one this good or if I have, this is a good tie with it.

Unfortunately we don't have a lot of headroom:
View attachment 288498

As a result, pops and ticks are going to distort and sound even worse. We can sweep for other frequencies:
View attachment 288499
Interesting that at higher frequencies it doesn't clip right away but distortion gradually increases.

Switching back to purely THD measurement (no noise), we can see very low distortion in MM and almost as good in MC:
View attachment 288500

Conclusions
SOTA's design partners (Wyn Palmer and Bill of Phoenix Engineering) have done a superb job of implementing RIAA equalization which is the heart of any phono stage. Distortion is very low and near top of the chart as well. Accurate measurements are provided which is a delightful and rare thing to see in audio. The only issue is low headroom requiring clean LPs to play, or alternatively, lack of sensitivity to pops and ticks. I wish power supply noise was lower as that would then land it at the top of the chart.

I am going to recommend the SOTA Pyxi phono stage.

----------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

excuse me because you may have certainly answered the question...
but why don't you counter the riaa..
the a-p certainly offers the correction...
it seems to me that at the level of the figures... the strong impact of the frequent problems of psu at "low frequency" under 1k... necessarily impact the figures in a significant way without this effort..
No?
;-)

 

[SIY]

a cartridge just sitting there does not close a circuit, so there would be no extra noise, that's what i measured at least.

At the very minimum, a cartridge MUST have Johnson noise- this is first principles physics. The inductance of MMs and impedance of the preamp input complicate things a bit, but the baseline Johnson noise and thus S/N ratio can be easily calculated for. Now I emphasize "baseline" noise, that is, the noise that physics enforces for perfectly ideal systems. In the real world, it's inevitably worse- for example, preamp current noise (which Amir does not measure) will degrade things further. If the cartridge is not connected to anything (in case this is an eristic exercise) it still has Johnson noise.

Here's a simple spreadsheet to calculate what your best case noise with an ideal preamp will be.

 

[WDeranged]

>>As a result, pops and ticks are going to distort and sound even worse

Do we have evidence that pop and ticks are reaching that level? 50mv is a 20dB headroom w.r.t. 5mv... looks like it should be enough?

I'd love to see a dedicated thread on this question. I can imagine a scratch or a very large piece of dirt generating a signal large enough to clip but I have doubts that the "normal" pops and clicks would be affected.

 

[Endibol]

This is a review and detailed measurements of the Pyxi Phono Stage by SOTA. It is on kind loan from a member and costs US $300.
View attachment 288488
Well.... the design is not going to win any awards with LED, power and MM/MC selector not being aligned. Operationally it is fine and I appreciate the loading dip switches being in the back rather than buried inside or underneath:
View attachment 288489
The AC transformer is rated at 14 volt/500 ma and as these tend to do, it gets a bit warm.

I large the large grounding screw. Measurements you are about to see are my best attempt at lowering the mains hum. Your setup may vary.

I like that the company provides detailed specifications in the manual. Here are the MM measurements and conditions:
View attachment 288490

SOTA Pyxi Measurements
Let's start with our usual dashboard in MM mode:
View attachment 288491
I wish the spike at 180 Hz was not there as it indicates noise from the power supply. It dominates SINAD which is still good but could be better (SINAD was varying a few dBs):
View attachment 288492

So definitely competent. Company specs a "THD" number. Assuming it really means that, i.e. there is no noise component, here is my measurement of that:
View attachment 288493

Close enough. Noise spec is provided a-weighted with the same 10 mv input and that is right on the money:
View attachment 288494

Back to our dashboard, MC mode with 0.5mv input is naturally worse:
View attachment 288495

But again it is dominated by power supply noise.

Most important measurement is implementation of RIAA equalization and here, SOTA does a perfect job:
View attachment 288497
I don't think I have ever measured one this good or if I have, this is a good tie with it.

Unfortunately we don't have a lot of headroom:
View attachment 288498

As a result, pops and ticks are going to distort and sound even worse. We can sweep for other frequencies:
View attachment 288499
Interesting that at higher frequencies it doesn't clip right away but distortion gradually increases.

Switching back to purely THD measurement (no noise), we can see very low distortion in MM and almost as good in MC:
View attachment 288500

Conclusions
SOTA's design partners (Wyn Palmer and Bill of Phoenix Engineering) have done a superb job of implementing RIAA equalization which is the heart of any phono stage. Distortion is very low and near top of the chart as well. Accurate measurements are provided which is a delightful and rare thing to see in audio. The only issue is low headroom requiring clean LPs to play, or alternatively, lack of sensitivity to pops and ticks. I wish power supply noise was lower as that would then land it at the top of the chart.

I am going to recommend the SOTA Pyxi phono stage.

----------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

@amirm Thank you for the review! I wanted to compare this to the IFI Zen Phono you reviewed some time ago, but it seems to have disappeared from the site.... Is it me or has it accidentally been removed?
Thanks!

 

[Rottmannash]

I have been mildly interested in buying a phono preamp but use the TT so seldom it's dropped low on my audio priority list (APL).

@amirm I assume you meant "like" when you wrote this sentence? " I large the large grounding screw "

 

[Soniclife]

What's even more important is overload recovery time. If a click or pop clips the preamp but the preamp recovers instantaneously, no harm no foul.

Clipping from surface noise with instant recovery should be better than not clipping from surface noise, it should be closer to the original recording.

 

[wynpalmer]

Now the fun begins...
First of all, subjectively the unit does not demonstrate any hum issues. In fact, extensive measurements have been performed and I've just repeated them on a couple of units- in MC and MM mode with shorts applied at the input with and without a 3m cable, with no issues. I've also been present in numerous listening/comparison sessions with no hum evident or reported. In fact, comments are made that the unit exhibits extremely low levels of audible hum.

Both are relative to the +13dBu ADC full scale level.

There are no plans to "improve" the power supply. The internal hum is extremely low.
I don't have access to an APX so I use an RME ADI-2 PRO FS R BE, and if I measure the response with the test loop (RME box DAC as a source, ADC as a measurement device) then the hum does appear, just as shown in the review. However, if I resistively attenuate the source (both the signal and ground potentials) by an amount comparable to the phono stage 1kHz gain, then the hum is substantially reduced. The input is configured for use with an explicitly floating source like a phono cartridge.
If anyone is interested, I'll provide other commentary as time permits- including on overload margin and the "unusual" softness in the overload characteristic versus frequency.
EDIT: Measurement was made using 96kHz, 2M samples, Blackman-Harris 7 window with 75% overlap and 16 averages.

 

[morillon]

pkane multitones offers the riaa correction
;-)

 

[abdo123]

At the very minimum, a cartridge MUST have Johnson noise- this is first principles physics. The inductance of MMs and impedance of the preamp input complicate things a bit, but the baseline Johnson noise and thus S/N ratio can be easily calculated for. Now I emphasize "baseline" noise, that is, the noise that physics enforces for perfectly ideal systems. In the real world, it's inevitably worse- for example, preamp current noise (which Amir does not measure) will degrade things further. If the cartridge is not connected to anything (in case this is an eristic exercise) it still has Johnson noise.

Here's a simple spreadsheet to calculate what your best case noise with an ideal preamp will be.

I'm not very knowledgeable here, but could you please comment on my rough measurements here:

Chord Huei Phono Preamp Review

In terms of overall system performance, the noise and distortion of the mechanical parts is usually much higher. The preamp may not be the bottle neck of the system. But the preamp of this bad performance will cause audible coloration. so from your statement of much higher noise from...

www.audiosciencereview.com

with the needle flying in the air i was mostly dominated by the ~90 dB SNR performance of my pre-amp, a stark difference from groove noise.