Pro-Ject Pre Box S2 Digital

Operating at 44.1KHz - no signal.

The point I’m making is that the PSU is very low noise - and the local switchers you refereed to are for Digital supply’s only and synchronized to a multiple of the audio clock to prevent any unwanted spurie folding back down into the audio band.

There is also twin Passive LC filtering between Digital and Analogue PSU domains to provide high frequency noise isolation, with active regulation taking care of the noise / impedance within the Audio B/W. The DAC regulator (in fact all analogue stage regulators) are individually cascaded to increase there PSRR.

The DAC’s analogue regulator loop BW covers the full audio BW - thereby reducing the negative sonic effects of bulk PSU capacitors etc. In fact the analogue regulation loop only reaches unity gain at a touch under 3MHz so it has exceptional BW for a PSU…

Exactly my point, but better said

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For sure the Jameco is the cheapest upgrade you can buy for the DAC - at US$11 does it matter if it only lasted a year… (not suggesting it would not last longer)…

John, any opinion on the sbooster power supplies? Much appreciated.

Agreed John, seems like a no brainer. Unfortunately it’s only an option for lucky 110V users but something for those that can, to consider.

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Yes - expensive!!!

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@John_Westlake have you gone for all linear regulators on this board, like LT3042’s for example? Or are there any switching regulators used?

Obviously this product was done within a budget and is REALLY nicely priced but I was just curious.

I tried zooming in on the available pics but my eyes aren’t too great.

All linear regulators in the analogue stage / clock circuits.

Answered in more detail in a few posts ealier.

If you can try with a decent external LINEAR PSU - it makes a bigger difference then it should, especially WRT Bass and sound stage.

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Nice! Jam packed with good stuff.

Thanks, I’m not sure whether the DAC will be operating in a mute mode without any signal applied. If the analogue output is muted, i.e a solid state switch which short the analogue output to ground when there’s no signal, then you may be measuring output shorted, this may explain why the SNR is so exaggerated high. I may be wrong here but it will great if you applied a 1kHz test tone and see if there’s any difference.

Guy,

I’m the designer of this DAC, you can be sure I know how it operates - the DAC PSU noise floor is REAL and not “exaggerated high” :slight_smile:

1KHz 0dB test tone does not elevate the noise floor, but you will see a low level spurie of the tone due to the finite impedance of the PSU and also due to the"kelvin sense" nature of the design - only at the point of the Kelvin sense “node” will you see the lowest PSU impedance - we have designed the PSU so that the DAC power pin is the Sense node - measure anywhere else on the PSU track and you will just see the PSU “modulating” to make the sense node “zero ohms”. The effective impedance is more or less the product of the regulator open loop gain at the frequency of interest - to insure there is adequate gain for low PSU impedance at 20KHz the unity gain BW is extend to about 3MHz.

The point of the FFT was to demonstrate that the PSU performance is not noise limited.

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Hi @John_Westlake ,I’m so sorry I didn’t catch you the last time you are indeed the designer of this product… My hat off man! Thanks for the information. It looks like the multi-stage switching PSU inside the DAC is indeed a good design.

I always have an impression that a single supply +5V DAC suffers from PSU noise due to use of multi-stage switching supplies inside the DAC as oppose of much traditional linear power supply regulation for full size DAC.

I liked the “I’m the designer of this DAC” part then we apparently moved from English to alien language :slight_smile:

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How do you think this look? Read good things about it.
http://www.ab-system.hk/index.php?route=product/product&path=73&product_id=64

Black is a shade, not a colour.

I’m using “UNI_Project_v4.38.0_Windows-Driver” on win 10 64bit.
After 2 hrs playing, the DAC get lost connection with PC.
On S2’s LCD, usb is connected but no sound.
It looks a driver issue. My guess is the driver has some memory issue.

I’m not sure… on my Win10 64bit system the same“UNI_Project_v4.38.0_Windows-Driver” works without any complications - for many hours.
May be you ought to let some IT guy to look at your “Windows”?

Is it just me, or is playback on this device around 7dB higher in level when MQA is engaged? Cleanest way to test in Roon is to toggle on/off sample rate conversion to a higher sample rate, which prevents MQA decoding but definitely shouldn’t affect the level.

Also – I’ve noticed that while the new firmware supports USB volume control, that controls volume before MQA decoding, so any reduction in volume via USB control messes up MQA decoding. Seems like a bit of a misfeature. I would imagine there’s a way to have USB volume control be at the same stage as the output control on the device – perhaps that will be a future improvement. (I’d also love to be able to switch inputs using the Roon “External Source Control” feature.)

Yes, MQA levels is higher, probably according to spec so people will perceive MQA as superior (MQA supplies the libraries to use in DACs) :slight_smile:

I think the current USB volume implementation is a digital volume inside the XMOS, and not a fully proper USB volume control (although I could be wrong here), which would explain why MQA information is stripped by it.

About driver issue: I have used it for a week now, playing all kinds of sample rates (mosty DSD512 native), and not discovered any drop-outs or other bugs. If you are powering it from USB, try using the supplied power supply (this will also give better SQ, despite what the manual might say).