SOTA Pyxi Phono Stage Review

[wynpalmer]

The gain for MM is ridiculously high at 45dB.

I recently tested a dozen or so phono RIAA stages I had lying around in various integrated and standalone preamplifiers for gain/overload. Typical average MM gain is around 35dB.

View attachment 288696

I cannot see how a highish output MM playing a few hot 12" 45rpm records isn't going to easily overload this little SOTA box.

View attachment 288697

BTW, the poorest performing phono stage was number 14, an AT USB turntable's integrated switchable RIAA stage. I knew it would be bad, but at 32mV overload @1kHz, it was was abominable. The SOTA's approx 50mV overload is IMO a disgrace. Clearly the result of power supply constraints, but combine that with such high MM gain and it's not a good choice.

The Pyxi is designed for use specifically with 2.5mv or so sensitivity cartridges in the "MM" mode. Possibly a little higher. This was specified by Sota and was not my choice. I proposed that a 35dB/45dB option be included for MM use but the choice was not to do so. If anything, the phono stage is more suited for MC than MM, and it does so excellently, in my opinion. It also is excellent for high output MC cartridges.
In fact, a 35dB/45dB MM only version exists and is just about to be "user tested". In this instance the input device is MOSFET rather than bipolar and the performance with real high inductance cartridges is better. I hope that none of these choices are "a disgrace" in your opinion.
Oh, and the Acrux has separate MM/MC inputs. As of this time the MOSFET MM inputs are about 5dB quieter than the Bipolar input Pixy for a Shure v15 III (1.3kR, 500mH) and the gain- SE- goes from 35 to 45 dB in 2dB steps, controlled by a front panel switch.
The clipping level will scale, inversely, with gain, as you would expect. Hopefully that, at substantially higher price, will be satisfactory.
Incidentally, the Pyxi has been used with a wide variety of MM cartridges. Most are 2.5mv sensitivity, but some that I am aware of are 5mv and they sound excellent. I do agree that the output level for higher output cartridges is too hot- the idea was to have something that approximated a standard CD compatible line input at about +6dBV max.

 

[amirm]

@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!

Yes, I took it out of the ranking due to test conditions being different.

 

[JSmith]

Quite a good phonostage it seems. Thanks for the testing @amirm, to the member that sent this in and to the designer @wynpalmer for participating openly in this thread.

Pyxi Phonostage – Sota Turntables

sotaturntables.com

For those that want to study the design philosophy behind the Pyxi and Acrux (available Summer 2023) feel free to read the whitepaper completed by Wyn Palmer.

JSmith

 

[amirm]

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 does. And is turned on at the source/generator. If you are asking to apply the inverse to the output, that would not represent reality. The phono stage has that gain and will amplify noise in the way you see in my measurements.

 

[pma]

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.

View attachment 288534
View attachment 288535


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.

The difference in your and OP’s 60 Hz leakage would be in system grounding. If “All-floating” concept is used, the mains frequency leakage is almost inevitable when measuring high gain, low level amplifying circuits. The one-point ground is important, probably provided by your RME.

 

[morillon]

It does. And is turned on at the source/generator. If you are asking to apply the inverse to the output, that would not represent reality. The phono stage has that gain and will amplify noise in the way you see in my measurements.

thank you
yes I was talking about a reverse riaa ..
I understand that indeed c is what will be seen at the preamp ...
( can be that for many, the presence of with and without reverse riaa would allow to relativize a little more in relation to the characteristics of the use of vinyl snr max etc.? I imagine that just a few clicks ;-) )

 

[voodooless]

It needs an AC supply. (half wave rectifier to produce split rails).

Ah, it has a bipolar supply then? From the PCB image it looks like it may use a Delon Voltage Multiplier. Those you indeed cannot feed with DC.

 

[pma]

Yes, there are much more ways how to make +/- Vs supply voltages from a single transformer output than a mere half-wave rectifier .

 

[Frank Dernie]

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.

Below about 2x the natural frequency of the mass on its suspension a seismic sensor - all cartridges are of this type - is not giving accurate reproduction.
How inaccurate is design dependant but it is always there and substantial.
Most of this is inaudible, of course, but the amplitude may indeed get sufficient to cause the bass drivers to be operating in a non linear area of their suspension and amplifier power be pointlessly wasted amplifying inaudible sub-sonic rubbish.

What is sometimes called a rumble filter is actually just a high pass filter and is good design housekeeping for such a transducer.

Not having one displays a lack of understanding of how record players fundamentally work, which is common in the hobby, sadly, with a lot of the information on the internet being just plain wrong.

I learned all this when designing seismic sensors in the early 70s and saw it fairly well understood in the industry when I worked on record players in the mid 70s. It isn't new and it is exasperating that the facts are often misunderstood or misrepresented.

A well engineered record transcription system with a seismic sensor would have a high pass filter built in.

 

[Frank Dernie]

Pxyi is a purpose built, not universal, phono stage

To reduce the effects of warped records, etc., SoTA makes some of the proven vacuum turntable series. Many of their turntables exhibit low unweighted ruble figures. All things being equal, the Pxyi is cost effective especially when used with the best 'tables in the SoTA range.
********
If folks require a rumble filter in a phono stage they should apply elsewhere.

Better, look at setup/placement and/or turntable/arm/cartridge system. There is plenty written on this and I'm not going to rehearse it here.

It isn't rumble that the high pass filter is needed for but to remove the subsonic rubbish inevitably produced by all pickup cartridges due to the way they work.
Warped records increase the amplitude of the out of the cartridges working frequency band output, but the reason it is there is physics and warps and rumble just exacerbate it.

 

[pma]

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

Power supply is designed properly.
From the Facebook photo:

Also, please check the manual:

https://sotaturntables.com/wp-content/uploads/2023/02/sota-pyxi-operating-manual-rev2.pdf

and technical explanations

https://sotaturntables.com/wp-content/uploads/2023/02/sota-pyxi-whitepaper.pdf

 

[voodooless]

Yes, there are much more ways how to make +/- Vs supply voltages from a single transformer output than a mere half-wave rectifier .

Yeah, if you’re not regularly into these things one quickly forgets how many topologies are actually out there

 

[Endibol]

Yes, I took it out of the ranking due to test conditions being different.

OK, I hope one day you can test it again under the new conditions. What has changed actually?

EDIT: Via the Search function the 2 if ZEN phone reviews (standard and Air) can be found again.

Thanks

 

[Waxx]

Not bad, but a bit expensive for what it is, especially with that noisy psu. It should be way better on specs or less pricey (relative) to be considdered good for me. Even my 8 years old Cambridge CP2 is much better and costed less (200€ at that time).

But it's not crap, that is true. On it's own it's quiet decent and enough to enjoy vinyl records. It's just overpriced for it's quality that is not top notch.

 

[pma]

Not bad, but a bit expensive for what it is, especially with that noisy psu.

We do not know what is the reason of 60 Hz residuals in the post #1 OP’s measurements. It rather seems to be a measurement system configuration issue and lack of defined system ground.

 

[restorer-john]

@voodooless & @pma

...there are two levels of regulation and a hefty amount of post rectifier filtering so the use of a half wave rectifier was inconsequential, and an inexpensive wall wart could be used...

The Pyxi supply is clearly different to the umbilical supplied, dual regulated, external PSU used in the Acrux:

But the relays in the pyxi appear to be 24VDC, so perhaps switched from rail to rail. Anyway, whatever it is, it is.

 

[restorer-john]

I think this phono stage offers excellent performance apart from the poor overload characteristics. But mated with a normal MM or particularly an MC, it is configurable enough to keep most people happy and $300 is not unreasonable in 2023.

The mains related spikes notwithstanding- I believe that's a measurement issue.

 

[morillon]

I think this phono stage offers excellent performance apart from the poor overload characteristics. But mated with a normal MM or particularly an MC, it is configurable enough to keep most people happy and $300 is not unreasonable in 2023.

The mains related spikes notwithstanding- I believe that's a measurement issue.

yes...(just other consumer products of the same kind often offer in this price range mm / mc)
just this 45db gain which really seems a bit surprisingly biased
;-)

 

[amirm]

The difference in your and OP’s 60 Hz leakage would be in system grounding. If “All-floating” concept is used, the mains frequency leakage is almost inevitable when measuring high gain, low level amplifying circuits. The one-point ground is important, probably provided by your RME.

Audio Precision has floating unbalanced connections for both output and input. I start there and often that produces the least amount of mains noise. AP does give the option to independently ground either channel for both input and output which I exercised here going through every combination to reduce the hum. Heck, I even reversed the polarity of the AC transformer to see if it improved any (it made it slightly worse so I went back to the first way I had it). As I noted in the review, this is the best I got.

So no, it is not a matter of "one-point" grounding (which is a fantasy anyway in unbalanced systems with components separated and many ways to get leakage currents). There are countless grounds here which cannot be tied together in any reasonable manner. Nor is there any assurance that the RME produced some magic here as it also has grounding issues to deal with (USB interface, its own switching supply, etc.).

Ultimately, phono stages are high gain products which invite such noise. Even if I could create very low noise, someone's system may not be so lucky.

 

[DSJR]

The gain for MM is ridiculously high at 45dB.

I recently tested a dozen or so phono RIAA stages I had lying around in various integrated and standalone preamplifiers for gain/overload. Typical average MM gain is around 35dB.

View attachment 288696

I cannot see how a highish output MM playing a few hot 12" 45rpm records isn't going to easily overload this little SOTA box.

View attachment 288697

BTW, the poorest performing phono stage was number 14, an AT USB turntable's integrated switchable RIAA stage. I knew it would be bad, but at 32mV overload @1kHz, it was was abominable. The SOTA's approx 50mV overload is IMO a disgrace. The result of power supply constraints perhaps, or passive RIAA losses? ,but combine that with such high MM gain and it's not a good choice.

Thank goodness the AT decks USB phono stage has a cartridge with around 3mV output (at 5cm/s) driving it then, rather than the usual 5mV (or higher sometimes) pickups..

Post #41 above tells all, so for MM pickups, I'd suggest AT 95 or 500 models as a starting point.


I also echo the move not to incorporate a sub-sonic filter to this device. Records usually have nothing cut on them below 40Hz (60Hz in DMM cuts I was told) and all you're getting is noise, cone flap and with smaller speakers, a huge amount of added distortion due to those things (most small boxes distort badly under 80Hz or so regardless of input and this affects the midrange too).

$300 seems rather a lot for what's inside. Do the dealers have a 50% margin on it I wonder?

---

Come back the 1967 Quad 33 preamp with sensible filtering below 35Hz (I thought the line stage also filtered the same but not so sure) and an acceptable overload if M2 was used on the disc input card. Many popular 80's UK made integrateds (Mission Cyrus both models, Arcam's smaller amps and so on) had filtering below 50Hz and the Naim Nait mk1 I remember, had an eq curve the inverse of typical cheap MM types 'we' all liked and sold... Output's low, but my Dada service kit fitted 33 is a fine little vintage preamp with surprising basic transparency and I love it to bits!