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Review and Measurements of Pro-Ject Pre Box S2 Digital

vkvedam

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This is a detailed measurement and review of Pro-Ject Pre Box S2 Digital. The unit is on loan to me from a kind member but it is one that I have been eyeing for good few months given the designer, John W, who is active on other forums. It was sold in Europe for a while until becoming available in the U.S. Retail price seems to be $399 and unfortunately not available on Amazon as of this writing.

View attachment 10718

As you see above, it is a very diminutive box compared to the Topping DX7/DX7s below it. It does have decent weight for its size and sticky feet so it is kind of supporting the heavy cables I have dangling behind it.

I always like to see a display on non-budget DACs as I like confirmation of what is being played, sample rate, format, etc. as often those can be transformed in software without the user knowing. The display here is small and grainy but good contrast. So for desktop use it is fine but in a rack, you need better eyes than me to see it from your seating location. :)

The buttons have a scratchy feel (rubbing against the case?) but otherwise have a very good feel. There are only a handful of options in the menu but despite that, it manages to create confusion with modes such as "Test" and "Best." Apparently the former generates best measured performance while the latter best sound according to the designer. Most of my tests are in "Test" mode with one exception where I show what "Best" does. There is also a distortion mitigation setting which I could not get to the bottom of as turning it on seemed to increase distortion, not reduce it! I will do more testing on this later but wanted to get this review out before that.

Most of the measurements are through S/PDIF input with signal generated from my Audio Precision Analyzer (see https://www.audiosciencereview.com/forum/index.php?threads/understanding-audio-measurements.2351/ on how I test DACs). USB tests were from my HP Z series laptop. Roon player was used in WASAPI exclusive mode. This worked initially but in later testing I had to set it to poll mode as opposed to preferered Event driven. No driver was necessary under Windows 10 Creator's edition.

Roon reports the following formats supported:

View attachment 10720

I tested the device using S/PDIF with USB connected and vice versa but did not detect any degradation in measurements. So isolation is good. For S/PDIF testing, I tested with the external power supply. With USB I tested both ways but it made no difference.

Measurements
Let's start with simple test of frequency response:

View attachment 10721

Even at this magnified scale we don't see any problems here. Response is just 0.2 dB down before the cut off which is a bit low at 18.6 Khz.

Next let's look at Jitter and noise over S/PDIF:

View attachment 10722

There are a few ticks here and there but they are down below -130 dBFs so really not a concern. Importantly there is no low frequency noise like there is in Exasound (see the green peaks on far left). Surprisingly clean for a device that uses switchmode power supply as there is no leakage current visible. Well done!

Next I compared USB to S/PDIF:

View attachment 10724

We see a rise in noise floor with some peaks and valleys. Nothing of audible concern but a bit disappointing.

NOTE: in re-testing for effect of power, etc. I could NOT duplicate this degradation. USB was just as clean as S/PDIF above. So not sure what causes this condition to show up. But again, not an audible or even a measurement concern due to very low levels.

Next let's look at how linear/faithful the DAC is as levels get smaller and smaller:
View attachment 10725

I am showing a comparison to Topping DX7. We see that while both reproduce "19 bits" faithfully according to my 0.1 dB of error cut off, the Pre S2 DAC is smoother than Topping DX7 before getting there. Mind you, we are at the limits of my analyzer here at nearly -120 dB so not an audible concern. But fair is fair and the Pre S2 does pull ahead a bit here.

Along the same lines let's see how a 24-bit file plays a -90 dB sine wave that is at the limit of 16 bit audio files:

View attachment 10728

Sorry about bolding of the graph on the right. Did not realize I had selected the graph when I captured it. Both are similar here and produce a very good sine wave. Only the Exasound E32 is superior (not shown) at 9X the cost.

Let's look at intermodulation distortion:
View attachment 10731

As we see here, Topping DX7 and especially Exasound E32 do better here.

Let's look at THD+N versus frequency:
View attachment 10732

Similar picture emerges with low frequencies having higher noise/distortion in Pro-ject Pre S2 Box.

Finally let's look at what happens with a 1 Khz tone when we filter it out and look at what is left (i.e. distortion and noise):

View attachment 10733

You can't see it but the S2 has higher second harmonic and that probably causes its measurements to suffer above. Further out as you see, it is competitive to better than Topping DX7. In all cases though the levels are very low and not an audible consideration for the most part.

As I promised, here is the difference in above test when selecting "Best" versus "Test" in the menu:

View attachment 10735

We see that "best" sharply raises the noise floor by some 25 dB! In doing so the noise now masks all of those distortion products. Seeing how there is some 32 dB of gain in the above measurements, the "best" mode likely has less signal to noise ratio than needed for 16 bit audio. When I have time I will do some listening and see if there is an audible difference. For now, I would probably use the DAC in "Test" mode. :)

Conclusions
The Pro-Ject Pre S2 Digital Box has an awful name but competently designed. I don't detect any aberrations in its performance. While it loses to Topping DX7 in a couple of tests, I don't think that will impact its audible performance. As a result the Pro-ject Pre S2 Digital DAC goes on my recommended list!

Note: The Topping DX7 is discontinued. I have the replacement DX7s here which I will review soon.

Edit: See the hardware teardown here: https://www.audiosciencereview.com/...-ject-pre-box-s2-digital-dac.2393/#post-67549
----
As always, I welcome comments, corrections, questions, etc.

If you like this review, please consider donating funds for these types of hardware purchase using Patreon (https://www.patreon.com/audiosciencereview), or upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
Hi Amir, just registered. Whatever you did so far is quite commendable, I shall donate :)

Question, why didn't you measure the 'Jitter' on S2?

Regards
Ven
 

geek101

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Seems like this dac is available for reasonable $$ in used condition. Anyone here noticed audible difference?. Do I have to use a certain filter for it perform well i.e just be a transparent line out device?.
 

geek101

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The manual talks about this, I am confused are they saying do not use external power supply if using usb?.
"2. USB input is in use: Unit can be powered directly from computer via USB input. In this case is highly recommended to disconnect Power 5V DC cable from the unit - power disturbances from two power supplies could affect sound performance."
 

dreite

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The manual talks about this, I am confused are they saying do not use external power supply if using usb?
Yeah, that is what they're saying. Some sort of conflict situation, I guess, that they don't recommend.

Steering diode schemes used to be in common use on equipment that had alternative power input options. When input voltage A was higher than input voltage B there wasn't any problem, but when voltage A equals voltage B you could see some weird effects.
I'm not sure if that's what the concern is here.

Dave.
 
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Anyone using this dac and have an opinion?.
I received mine last week. It's a nicely built and compact device. I can't say much about the sound quality other than it sounded very good to my ears.
The problem for me is that the Pre Box has a pretty severe issue with playing MQA audio. Some albums play without issue and others switch constantly between MQA and PCM playback, resulting in audible "drops". I observed this in Tidal but there are reports of it happening in Roon as well. You can read more about it here: https://community.roonlabs.com/t/mqa-dropouts-during-play/36430.

For me this was a deal breaker, especially at the price. If you don't use MQA, the Pro Box might still be a good device for you.
 

Music1969

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The problem for me is that the Pre Box has a pretty severe issue with playing MQA audio. Some albums play without issue and others switch constantly between MQA and PCM playback, resulting in audible "drops". I observed this in Tidal
This is a known bug with the DAC. But if you have Tidal do the 1st unfold, the bug disappears. You’ll see “MQB” on the DAC screen.
 

Music1969

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Could a firmware update fix such a thing?. Seems like a serious issue.
Not a serious issue. If you're playing with MQA, you likely have Tidal. The Tidal desktop app is free if you have Tidal. Just make the Tidal app do the 1st unfold and the issue disappears forever.

If you have Roon or Audirvana, do the same and there is no issue.

If you don't care for MQA, there is no issue.

They said they are working on a firmware update but the fix is so easy (following the above), it doesn't matter if an update never comes.

Other than this known MQA bug, this DAC is rock solid. No other issues I've seen reported.
 
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Anyone using this dac and have an opinion?.
Yes, and rather satisfied being good value for its money.

The only remarks I have:
- when you leave the device on, the screen burns in
- no firmware updates seen after the developer left, so no idea if the few known issues will ever be resolved
- support has not been responsive in my case.
 

Music1969

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Last edited:
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Maybe I missed it, I am new, but a bit of a lurker. Why isnt this dac included in the SNR charts?
 

Veri

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Maybe I missed it, I am new, but a bit of a lurker. Why isnt this dac included in the SNR charts?
These are done with @amirm old analyser, everything in the current charts is used with the new APx555 so that it is consistent. The old results with a different analyser machine can't be included, because it isn't entirely the same set-up. Since it's a loaner, the measurement can't be simply 're-done'.
 
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Thanks for the info!

trying to find something to possibly replace my Dac magic 100, preferably is XLR, that also isnt silly expensive. but it is a "fun" search
 

AudioSceptic

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These are done with @amirm old analyser, everything in the current charts is used with the new APx555 so that it is consistent. The old results with a different analyser machine can't be included, because it isn't entirely the same set-up. Since it's a loaner, the measurement can't be simply 're-done'.
Is there a way of calculating/estimating SINAD from those older tests? It would be great if they could be included in the "big chart", with perhaps a ? or something against the number to indicate that they are estimates.
 
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