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Hardware Teardown of Pro-Ject Pre Box S2 Digital DAC

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#41
I don't understand why gear is purchased if it doesn't perform to expectations. Cut your losses. Sell what you have and buy something better. Modding is usually like putting lipstick on a pig. :oops:
Hey, dude, I haven't bought anything. Just researching and learning on the process. Mind your own business.

Thanks DonH56, trl and amirm for your answers.
 
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#42
This will reduce noise floor and jitter as well
It would be conventional to power any clock recovery circuits from their own, low noise supply. Anyway, input jitter stops at the DAC clock (provided you are using the DAC clock as system master clock, and using a data pull protocol, rather than a data push protocol).

But your other comments make little sense to me.

The digital side of the electronics is just that; digital. It involves relatively large swings, at high frequencies, generating a huge range of digital noise. In the early days of ASIC design, I had to use a tool to analyse the internal ground bounce of the chip, to ensure that the supply rails didn't actually cross (i.e. reverse the supply polarity) when the clock switched; that's how bad the noise was. A bit of noise from the power supply is going to have negligible effect. So a low noise PSU is unnecessary on the pure digital circuits (barring clock recovery, which isn't digital). You might want to power the PCM output buffers to the DAC from a quiet PSU, to reduce noise coupling to the DAC.

Since there will be some coupling between digital and analogue supplies in the DAC, there's an argument that you might want to power the digital side of the DAC from a low noise linear PSU. But, again, the noise generated by the internal digital signal swings will massively dominate this noise.

The DAC analogue section certainly needs a low noise linear PSU, as any PSU noise will bw coupled into the output signal.

Arguing that the CMRR of op amps means that you don't need to use a low noise linear PSU for the analogue is just perverse, given that you have suggested powering the digital electronics from such a supply. A high CMRR is good, but why not help things along with a clean PSU anyway? A low noise linear PSU is cheap enough, as it only needs to be low power.
 

trl

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#43
Thanks for pointing this out!

However, I was having no SNR differences at the end of audio chain when using 0.5mV PSU vs. 5mV PSU (AC ripple & noise peak-peak) when powering regular LM4562/LME49720 in I/V, LPF, VAS and BUFFER stages and 5mV of ripple and some noise for the analog audio parts is quite nasty I'd say (rails: +/-12V). Most likely with 20mV of ripple or more entire analogue signal will have to suffer, but haven't tested this.

As for DAC analogue voltage rails I'm 110% sure AKM are not silly when telling us about the importance of low-noise PSU and decent decoupling on their DAC's analogue rails, so low noise PSU here (uV RMS) definitely matters. :)
 

Mark Dirac

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#44
I cannot take it apart! I have removed the two screws on the base. And also the two screws on the rear panel (although I do not think these need to be removed?) But the sleeve will not slide off.

Anything I am missing please? How should it come apart? How hard should one pull the sleeve?#!
 

RayDunzl

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#46
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amirm

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Thread Starter #47
Anything I am missing please? How should it come apart? How hard should one pull the sleeve?#!
You have to take the front knob off, then the screw that holds the shaft. Then you slide it off.
 
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Thread Starter #48

Mark Dirac

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#50
You have to take the front knob off, then the screw that holds the shaft. Then you slide it off.
Thanks. But ... how take the front knob off? There's no screw holding on the knob. I've pulled on it quite hard. (I can see I'm going to end up with a broken DAC at this rate.)
 
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Thread Starter #51
Thanks. But ... how take the front knob off? There's no screw holding on the knob. I've pulled on it quite hard. (I can see I'm going to end up with a broken DAC at this rate.)
I don't have it with me anymore but I am pretty sure it is just friction fit. And they can be quite stiff. So just yank harder but don't call me if you break it. :D

One way to know if it is moving at all is to wedge the front of your thumb between the knob and the front panel and then try to slowly pry it off. You will be able to sense with your thumb if the distance is increasing or not. If the distance is increasing then continue and it should just come out.
 
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Thread Starter #52
Oh wait, looking at my picture it seems that you can take off the back just the same. Take out all the screws there and pull off the back panel. Then pull from the front to slide it out.
 

Wombat

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#54
Hey, dude, I haven't bought anything. Just researching and learning on the process. Mind your own business.

Thanks DonH56, trl and amirm for your answers.
Touchy, touchy. You are free to do as you please. You don't need my permission. Grow up.:eek:
 
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#55
Thanks Amir for advice on getting inside the product. But - beware others - your recollection was unfortunately not correct. It was careless of me to ask you to remember how to do this, given that you borrow many products and only ever have them in your possession for a short while - apologies. More appropriate instructions for getting inside are in this thread summary Google Doc.
 

Music1969

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#56
Hi @amirm

From looking at the photos - how do you think the analogue filtering is being done?

Especially considering this DAC supports DSD64 to DSD512, I would assume analogue filtering is important to filter out this quantization/ultrasonic noise.

Obviously there would be on-chip filtering by the ESS Sabre chips but after that, what is doing the analogue filtering before RCA outputs? From looking at the photos.

I know we can't hear ultrasonic frequencies but I assume it's still important to filter out in the analogue domain?

And what is the Axicom V23105A5001A201 relay used for here?

Thanks in advance
 
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Thread Starter #57
I am too lazy to reverse engineer it much beyond the original teardown. :) The relay is there to disable the output in case of the DAC popping as sample rate and such is changed.
 

helom

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#58
That is usually the case. But somehow the problems I typically see with switchmode supplies are NOT visible in Pro-Ject S2. I suspect they selected a switching wal-wart that doesn't have mains leakage.

In general in this price range I like to see a larger box with a linear power supply in it.
I have this DAC and its SMPS was inducing a buzz noise into my analog/phono setup. I've since replaced it with a Topping P50 power supply and it solved the problem.
 
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#59
The only thing that raises the eyebrow is use of cheap electrolytic caps from Lelon. For this price range, spending another $10 on better caps would have been nice to see.
Pro-ject seem to have carefully selected the caps according to the attached product leaflet. Perhaps there are other reasons for the selection other than cost? I have ordered one of these units and it is due to arrive tomorrow. As Charles Dickens said: I have 'Great Expectations'.
 

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Thread Starter #60
Pro-ject seem to have carefully selected the caps according to the attached product leaflet.
You mean this?
1578299726826.png


I doubt there is anything organic about said caps. :)
 
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