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Review and Measurements of Pro-Ject Pre Box S2 Digital

amirm

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#1
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.

Pro-ject Pre Box S2 Digital DAC 20180217_140621.jpg


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:

upload_2018-2-18_9-24-45.png


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:

Pro-Ject Pre Box S2 DAC Frequency Response Measurement.png


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:

Pro-Ject Pre Box S2 DAC Jitter Measurement.png


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:

Pro-Ject Pre Box S2 DAC USB Jitter Measurement.png


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:
Pro-Ject Pre Box S2 DAC Linearity Measurement.png


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:

Pro-Ject Pre Box S2 DAC -90 dB linearity Measurement.png


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:
Pro-Ject Pre Box S2 DAC SMPTE Intermoduation Distortion Measurement.png


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

Let's look at THD+N versus frequency:
Pro-Ject Pre Box S2 DAC THD+N Measurement.png


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):

Pro-Ject Pre Box S2 DAC Residual noise and distortion Measurement.png


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:

Pro-Ject Pre Box S2 DAC Residual best vs user Measurement.png


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).
 
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#2
Thanks Amir for the review. A little disappointed with the harmonic distortion tests but otherwise very excited about the results. Those two units are very competitive with a the edge going to the topping being a bit cheaper and with more I/O optoins.

One thing about the tests of the Pro-ject, did you look at the head-amp at all or do you plan on adding some measurements of it later?
 
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#5
Maybe I got that idea from the massdrop price, was it reduced? Also, I guess that would be for the DX7s as thus may not be applicable here depending on how that unit measures. I was talking about the two topping interchangeably, maybe should hold off on that.
 

Sal1950

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#6
Hummm, another good review of a reasonably priced product. Great overall measurements.
What will the "your just out to get us" complainers have to support their claims now?
 
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#7
Nice to see another well performing dac in the lower price range.

Might be worth mentioning, this dac supports MQA. I have no interest in MQA myself, but this good budget option for those that want this feature.
 

amirm

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#8
Nice to see another well performing dac in the lower price range.

Might be worth mentioning, this dac supports MQA. I have no interest in MQA myself, but this good budget option for those that want this feature.
Yes. Meant to mention MQA but forgot. :)
 

Jerry Sobel

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#9
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.

----
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).

Another excellent review. Donation made. Keep'em coming! Cannot wait to see how the DX7s does.
 
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#11
Thanks Amir for the review.
I wonder about the distortion compensation setting. In "test mode", it is enabled with Brickwall filter selected. In "best" mode it should be disabled with optimal filter enabled, and your last test confirm this. Huge difference! Probably the better wording for "Best mode" should be "Distortion mode". ;)
However the question is how to enable it in User mode, because if I read you correctly in user mode the On on the display means Off on the chip. If you confirm this I can raise it as a bug to be fixed in next firmware release. (Does your unit uses v2.12 of the firmware?) Or maybe the trick is to select Test mode and then just play with the filters without touching the compensation setting :)
If you have time I would love to see if you find any differences in performance of USB input without SMPS ( USB power only) and/or with LPSU.
Jussi Laako (HQ player) in his measurements found that clearest output from the DAC was when he was using DSD 512 signal. For PCM: DC On and Fast Rolloff filter.

Good to see that at a fair price companies like Topping or Pro-ject deliver well built hi-res ready DACs. Few years ago probably for this kind of performance you would have to pay premium price.
PS. Are you also planning to document how the unit is built inside?
 
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#13
First post here, prompted by some interesting measurements/discussions.

I picked up the Pro-Ject Pre Box S2 Digital a few months ago, I think on the same day it was first officially available in the US, so I've had a fair amount of time to play with it. It's been an interesting little unit. A lot of functionality and quite pleasing sound. There are, however, a number of firmware/operational issues with it that do not seem to have been successfully addressed yet, that prospective purchasers should research before buying.

Anyway, a question or two for @amirm - if you'll be kind enough to indulge a new poster.
  • What firmware revision is on the Pre Box S2 Digital you measured?
  • Did you observe that selecting "Test" puts the unit in "Brickwall" filter mode and changing the filter to anything else puts the unit back in "User" mode?
Just for fun, I did a quick set of very basic frequency response "measurements" to get an idea of the characteristics of the different selectable filters (mostly to see if there was any measurable change at all). Nothing fancy here, just stuff done while on the go and without access to "real" instruments. ADC was just that in the Arturia Audiofuse. Input was USB. 24/48 source signal.

Pre Box S2 Digital - FR-per-Filter.jpg


Incidentally, for those interested in buying one, you will find the unit on Amazon (via Audio Advisor) when they actually have it in stock, which is how I got mine.
 

amirm

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#14
I wonder about the distortion compensation setting. In "test mode", it is enabled with Brickwall filter selected. In "best" mode it should be disabled with optimal filter enabled, and your last test confirm this. Huge difference! Probably the better wording for "Best mode" should be "Distortion mode". ;)
Hi there. We have been having a discussion about this. I need to do more testing but in preliminary measurements, Enabling distortion compensation seems to raise distortion, not lower it! Since this is backward I like to perform more tests and only post them when I am sure.
 

amirm

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#15
If you have time I would love to see if you find any differences in performance of USB input without SMPS ( USB power only) and/or with LPSU.
I tested this with and without its wal-wart plugged in and it made no difference. Testing with LPSU requires a mini-USB jack. I made one but seemingly it has gone shopping or something because I can't find it. :D
 

amirm

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#16
Anyway, a question or two for @amirm - if you'll be kind enough to indulge a new poster.
  • What firmware revision is on the Pre Box S2 Digital you measured?
Welcome to the forum. That is one cute Avatar you have! :)

The version number is 2.12. What should I be running?
  • Did you observe that selecting "Test" puts the unit in "Brickwall" filter mode and changing the filter to anything else puts the unit back in "User" mode?
Yes, if you make any changes in US, it says "user" mode. In my case changing distortion compensation would put it in user mode.
 
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#17
> what happens with a 1 Khz tone when we filter it out

Amir, I'm still lost pondering this unfamiliar unit, the kelvin-hour-z (Khz).

What exactly is a kelvin-hour-z tone?

I can't find a reference to its definition, anywhere.

Any help greatly appreciated!
 

amirm

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#18
This is my unit and I gave him permission to open it up for hardware tear down. So I would think that this should be coming in the near future. Looking forward to what he finds there as well.
Yes, surgery to come later. :D
 
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#19
The version number is 2.12. What should I be running?
2.12 is the latest that I'm aware of, and I don't know of any audible/measurement reason to run anything else. Though for some reason 2.12 was, apparently, pulled from distribution (maybe it's back now).

I do know that 2.12 does NOT properly fix the MQA drop-out issue. It improves the situation (i.e. it occurs less frequently, and recovers automatically), but does not rectify it fully. Not a big issue for me personally, but for those interested in it for reasons of playing MQA content, it's worth being aware that issues remain there.

There's a thread here that talks about the various issues and the firmware situation.
 

mindbomb

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#20
> what happens with a 1 Khz tone when we filter it out

Amir, I'm still lost pondering this unfamiliar unit, the kelvin-hour-z (Khz).

What exactly is a kelvin-hour-z tone?

I can't find a reference to its definition, anywhere.

Any help greatly appreciated!
lol. yes, the wrong letter was capitalized. kHz.
 
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