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SOTA Pyxi has arrived

wyn palmer said:
(...) It is possible to reduce the gain from 45dB to, say, 36dB, but with some loss of RIAA compliance accuracy. The next version of the Pyxi may well have this option, but it was decided by SoTA to not have it in the first version. (...)
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I'd deem an additional MM gain setting of roundabout 34 dB a good idea - 'cause that would ensure decent compatibility with devices, that are designed to cope with the usual maximum output of "modern" digital sources, i.e. ~ 2 V @ 0 dB(fs), but not really more than that. Although one could of course argue, that such devices could still have a problem with such a Pyxi version in combination with very loud DJ carts and very "hot" cuts - but I'd think, that one can't really expect a phono stage for roundabout US$ 300 to cover all bases (or at least not, if it's foremost designed for premium hifi quality rather than universal compatibility...).

Greetings from Munich!

Manfred / lini
 
wyn palmer said:
The architecture of the phono stage is - as far as I can tell - unique. It makes it hard to switch gains. It is possible to reduce the gain from 45dB to, say, 36dB, but with some loss of RIAA compliance accuracy. The next version of the Pyxi may well have this option, but it was decided by SoTA to not have it in the first version.
As for a comparison with the Curl design. It is of course up to the listener to decide, but the specs of the Pyxi are superior, and in two instances that I am aware of "the listener" concluded it was audibly better.
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Would an attenuator made from a series and parallel resistor (closely matched) compromise the performance of the Pyxi?
 
lini said:
I'd deem an additional MM gain setting of roundabout 34 dB a good idea - 'cause that would ensure decent compatibility with devices, that are designed to cope with the usual maximum output of "modern" digital sources, i.e. ~ 2 V @ 0 dB(fs), but not really more than that. Although one could of course argue, that such devices could still have a problem with such a Pyxi version in combination with very loud DJ carts and very "hot" cuts - but I'd think, that one can't really expect a phono stage for roundabout US$ 300 to cover all bases (or at least not, if it's foremost designed for premium hifi quality rather than universal compatibility...).

Greetings from Munich!

Manfred / lini
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It depends on the sensitivity of the cartridge. I've digitized thousands of albums, including "hot" club recordings and the output has never exceeded 14dB higher than the rated sensitivity. I know this because, well, I'm very anal about such things, and I set the digitizer for a certain sensitivity and note the peak level in dB below FS.
The Pyxi has c. 27dB overload margin relative to its rated sensitivity (2.5mv rms @ 1kHz, 5cm/sec), and it's more or less frequency independent due to the unusual architecture employed.
The nominal output is -52+45=-7dBv and the absolute peak is +5dBv, leaving 10dB before clipping, and 1dB below your 2v (+6dBv) input level.
Dropping the gain to c. 35dB would make the sensitivity c. 7.5mv and retain all of the margins, relatively.
This would probably be done with an internal pair of jumpers, one per channel, and not an external switch, which may or may not be acceptable, and is certainly not ideal.
 
cgallery said:
Would an attenuator made from a series and parallel resistor (closely matched) compromise the performance of the Pyxi?
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See the previous post. You don't want to risk the possibility of clipping, and the distortion worsens as the level goes up. The Pyxi is specified at the maximum output consistent with 12dB overdrive beyond the input sensitivity and degrades beyond that. The spec is a bit worse than what the unit actually delivers, but I don't know at what point it fails to meet spec.
 
You could exchange two internal resistors with different SM values if you want to stick to a given gain, but you'd invalidate the warranty in doing so, and I don't recommend it.
For example, two 18 ohm Rs would become 56 ohm Rs for a gain of c. 35dB. You'd still have the extra 20dB gain step when you switch to MC.
Again, I don't recommend it, but it is doable.
 
Wyn,
How close is the Pyxi to your DIY design that spawned several threads and countless posts?
I built one and I prefer it over my built-in phono stage.
Is the upcoming (more expensive) SOTA preamp closer to that design?
 
wyn palmer said:
You could exchange two internal resistors with different SM values if you want to stick to a given gain, but you'd invalidate the warranty in doing so, and I don't recommend it.
For example, two 18 ohm Rs would become 56 ohm Rs for a gain of c. 35dB. You'd still have the extra 20dB gain step when you switch to MC.
Again, I don't recommend it, but it is doable.
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I'll keep this in mind, as 35/55 would be about ideal for me.
 
Jeff449 said:
Wyn,
How close is the Pyxi to your DIY design that spawned several threads and countless posts?
I built one and I prefer it over my built-in phono stage.
Is the upcoming (more expensive) SOTA preamp closer to that design?
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The upcoming commercial one is closest to the evolved DIY one. It has the dual input opamps, the warp filter (improved), relay switched output delay, and balanced/SE output. It's slightly noisier than the final DIY with AD797s or LT1115s.
It will also have a revision before being marketed, so the noise will likely improve slightly in the MC case.
The Pyxi is closer to the earlier revisions, however the front end section with the RIAA is essentially the DIY MM one, but with bipolar input opamps (OPA1612). The MC extra 20dB gain is supplied in the output stage.
All the SoTA designs use dual linear regulators per channel, rather than a SMPS with an add on filter. The Pyxi uses a 14v wall wart with a floating AC output as the source.
Close tolerance Rs and Cs are used, and all of the units embed a phase compensated DC feedback loop to set the LF frequency and make the unit low DC offset; the same overall architecture is applied to obtain the RIAA accuracy, high frequency independent overload margin, excellent supersonic rejection etc. etc.
 
Wyn: So would you think, that Shure's old study results (republished for example over there: http://pspatialaudio.com/max_velo.htm) were pretty exaggerated?

But anyway, a gain of 45 dB would mean a maximum input level of not quite 11.25 mV, if the output level shouldn't exceed 2 V - and for an MM with a pretty typical output level of 5 mV (at 1 kHz and 5 cm/s peak in 45°/stereo modulation) that doesn't leave a big margin.

Greetings from Munich!

Manfred / lini
 
lini said:
Wyn: So would you think, that Shure's old study results (republished for example over there: http://pspatialaudio.com/max_velo.htm) were pretty exaggerated?

But anyway, a gain of 45 dB would mean a maximum input level of not quite 11.25 mV, if the output level shouldn't exceed 2 V - and for an MM with a pretty typical output level of 5 mV (at 1 kHz and 5 cm/s peak in 45°/stereo modulation) that doesn't leave a big margin.

Greetings from Munich!

Manfred / lini
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Things to consider.
1. The max level that I have measured is not frequency dependent. It's after deemphasis- i.e. the output from the phono stage.
2. I have no idea what the frequency distribution of the input is, so I cannot back compute the peak velocity.
3. The values of the FS setting is in RMS, not peak. An assumption is built into this that the peak is 3dB higher (i.e. 5cm/s rms is equivalent to c. 7cm/s peak)
4. If the max were at 1kHz, then the peak velocity would be 5cm/sec (nominal output rms) x 5 (14dB higher) x 1.414 = 35.4cm/sec, and more typically 5x4x1.414=28cm/sec, in my experience.
5. If the peak were at a higher frequency, then the velocity would be higher, due to the RIAA de-emphasis curve.

I believe that my results are in conformance with Shure's results, and I have seen this article before, but it was nevertheless reasonable for me to do my own "research".

Anyway, if you assume that the MM is 5mv @1kHz/5cm/s then all of my numbers would have to be scaled accordingly. Most, if not all, 2v rms input channels have substantially higher overload levels, so an extra 6dB is of little, if any, consequence, and the phono stage itself cares little. It improves the S/N and although the distortion degrades it's still extremely low and below the dynamic acoustic threshold which would mask the products.
In any case. It was not my choice to go for 45 dB. It was SoTA. I actually wanted it to be a tad lower, as was the case with the DIY stage.
 
Wyn: No worries - for me it wouldn't be a problem, anyway. But in some cases it actually is, because there indeed are devices, that have problems with input levels over ~ 2 V(eff.). That foremost goes for soundcards and sound interfaces, that don't sport a proper level or respectively gain control on the analogue side. And hence I'd deem such a lower gain setting around 34 dB a good idea to make the Pyxi interesting for even more cutomers.

Greetings from Munich!

Manfred / lini
 
Damn it, just received, a couple days ago, a Mani 2 I ordered. "Watching" this thread, this can be my next test drive.
 
lini said:
Wyn: No worries - for me it wouldn't be a problem, anyway. But in some cases it actually is, because there indeed are devices, that have problems with input levels over ~ 2 V(eff.). That foremost goes for soundcards and sound interfaces, that don't sport a proper level or respectively gain control on the analogue side. And hence I'd deem such a lower gain setting around 34 dB a good idea to make the Pyxi interesting for even more cutomers.

Greetings from Munich!

Manfred / lini
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It's easy to add a 6dB pad before the succeeding line stage, although not the neatest of solutions. In the original DIY design a pad could be added before the output buffer, and an extra gain stage could be added- all built into the board. These features disappeared when the balanced configuration was used.
The gain could also configured for a lower value, although several components needed to change. With the Pyxi, that is not the case as only one component needs to change per channel- perhaps next revision SoTA will include it.
 
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