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Project Pre Box S2 DAC & Headphone Amp Review

amirm

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#1
This is a review and detailed measurements of the Project Pre Box S2 Digital USB DAC and Headphone Amplifier. It is on kind loan from a member. The S2 costs US $399 including Prime shipping from Amazon. I reviewed an early unit before I have my new audio analyzer so request was made to measure it again so here it is.

The S2 is a compact box with a color but grainy LCD:

Project Pre Box S2 Digital USB DAC Audio Review.jpg

Dedicated filter and Menu buttons make navigation easy.

The back panel has the usual connectors:
Project Pre Box S2 Digital USB DAC Back Panel Connectors Audio Review.jpg

Since I tested the S2 using its USB port, I did not have to supply external power to it. Lack of external supply likely limits its headphone output level.

The S2 supports MQA which is still rare in lower end audio DACs.

The S2 uses ESS Sabre DAC which has a distortion compensation feature. The S2 is the only DAC I know that lets you turn that feature on and off. You will see its effect in measurement section.

DAC Audio Measurements
Let's start with our usual dashboard:
Project Pre Box S2 Digital USB DAC Audio Measurements.png


Even though distortion compensation is ON, we still have rather high second harmonic which brings SINAD which is sum of distortion and noise relative to main signal down fair bit. The ranking straddles two of our buckets:
Best USB DAC Reviewed.png


This is not a good first impression for a product in this price range. I thought the news would be bad from here on, but that was not the case. The S2 produces a very quiet background: (should say 20 bits, not 20 dB)
Project Pre Box S2 Digital USB DAC DRN Audio Measurements.png


This is just a few dBs shy of state of the art.

Good news continued into linearity measurement:
Project Pre Box S2 Digital USB DAC Linearity Audio Measurements.png


And jitter & noise measurements:
Project Pre Box S2 Digital USB DAC jitter Audio Measurements.png


The low noise floor gave the S2 a leg up in the IMD versus level in the noise-dominated portion of that graph (sloping down):
Project Pre Box S2 Digital USB DAC IMD Audio Measurements.png


As levels increase though, distortion takes over.

ESS DAC implementations tend to have a mid-level bump up in the above measurements. Manufacturers have lately been able to conquer that. Interesting that the S2 despite being an older design, is completely clear of that issue. So the secret was known earlier among some designers.

Multitone results are more hopeful than SINAD:
Project Pre Box S2 Digital USB DAC Multitone Audio Measurements.png


THD+N versus frequency swings back to disappointing side of the fence:
Project Pre Box S2 Digital USB DAC THD vs Freq Audio Measurements.png


Filter response is standard affair:
Project Pre Box S2 Digital USB DAC Filter Response Audio Measurements.png


Distortion Compensation
Turning off distortion compensation reduces performance substantially:
Project Pre Box S2 Digital USB DAC distortion Compensation off Audio Measurements.png


Can't imagine why you would want to turn this feature off.

Headphone Amplifier Measurements
Let's start with our noise measurement at just 50 milivolts to see if the quiet DAC noise floor shows up here:
Project Pre Box S2 Digital USB DAC 50 mv Headphone dynamic range Audio Measurements.png


Looks like the eye was taken off the ball here:
Lowest Noise Headphone Amplifier.png


Sensitive IEMs will likely have some amount of background hiss at elevated volumes.

Power into high impedance load of 300 ohm is quite low:
Project Pre Box S2 Digital USB DAC Headphone Amplifier Output 300 Ohm Audio Measurements.png


Yet again we see elevated noise levels. The headphone amp is definitely noisier than the DAC portion.

Ditto for 33 ohm load:
Project Pre Box S2 Digital USB DAC Headphone Amplifier Output 33 Ohm Audio Measurements.png


This is very low power level. Hard to imagine a desktop product shipping with such low output level.

I thought maybe output impedance is high but it is not (thankfully):
Lowest Impedance Headphone Amplifier.png


Listening Tests
Not feeling good so I skipped listening to the S2. The numbers speak to inability to reach any decent level of loudness without distortion.

Conclusions
There are some really bright areas in performance of Pre Box S2. Its DAC has excellent noise floor, great accuracy in the form of linearity, and very low jitter. Distortion is high though for the class. That may not be an audible thing but the very low output levels of the headphone amplifier certainly is.

There are many good choices in this price range and lower so I can't recommend the Project Pre Box S2. But if you find a used one, pair it with a good headphone amplifier and you would be good to go.

--------
As always, questions, comments, corrections, etc. are welcome.

Was not feeling good per above and went to the doctor. He said I have MSD. I asked him what that was and he said: Money Starvation Disease. I asked him for the cure, he said it would come in the form of donations form you all. Of course the son of a gun took more money from me, making my symptoms even worse! Please help dig me out of this disease by donating using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
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amirm

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#3
This is a design by an active online overseas designer, marketed and sold under the Pro-ject name. Pro-ject is best known for their low cost turntables. So we can't interpolate to their future products unfortunately.
 

Veri

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#4
In the old review dist compensation 'off' was 'on' and vice versa right? This is fixed now? :)
 
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#5
Yea I've heard the all in one, was never impressed

The standalone DAC tho is pretty nice. Likely not the most aggressive priced thing given the current state of the market
 

amirm

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#6
In the old review dist compensation 'off' was 'on' and vice versa right? This is fixed now? :)
Yeh, seemed reversed in that unit.
 

amirm

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#8

Rja4000

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#9
Nice review, as usual :)
I was wondering if the problem is not due to USB power.
Could you try some with external power supply?
Like IMD vs level and output power at low impedance?
 

miero

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#10
In EU this device is being sold with a (low quality) switching power supply. But authors recommends to use an external linear supply.

@amirm would you be able to repeate some tests using a laboratory power supply?
 
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#11
Maybe Pro-ject Accu Box S2 ?
I see that I have succeeded in buying the new SMSL M500 for my Tidal MQA lists. The SMSL is so far away in terms of resolution, noise and headphone power. SMSL total success....

 
Last edited:
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#12
Wow, an interesting piece! Excited for the future of this company :)
What? An interesting price? 400$ for basically just the DAC (even with the external power, HP out would not give that much more) is interesting? You would freak out of Topping D10 then, less than 1/4 S2's price.
Not just that, DX3 Pro would be more than twice the AiO device for 1/2 of the price compared to this S2.
 

AudioSceptic

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#14
This is a review and detailed measurements of the Project Pre Box S2 Digital USB DAC and Headphone Amplifier. It is on kind loan from a member. The S2 costs US $399 including Prime shipping from Amazon. I reviewed an early unit before I have my new audio analyzer so request was made to measure it again so here it is.

The S2 is a compact box with a color but grainy LCD:


Dedicated filter and Menu buttons make navigation easy.

The back panel has the usual connectors:

Since I tested the S2 using its USB port, I did not have to supply external power to it. Lack of external supply likely limits its headphone output level.

The S2 supports MQA which is still rare in lower end audio DACs.

The S2 uses ESS Sabre DAC which has a distortion compensation feature. The S2 is the only DAC I know that lets you turn that feature on and off. You will see its effect in measurement section.

DAC Audio Measurements
Let's start with our usual dashboard:
View attachment 40320

Even though distortion compensation is ON, we still have rather high second harmonic which brings SINAD which is sum of distortion and noise relative to main signal down fair bit. The ranking straddles two of our buckets:
View attachment 40321

This is not a good first impression for a product in this price range. I thought the news would be bad from here on, but that was not the case. The S2 produces a very quiet background: (should say 20 bits, not 20 dB)
View attachment 40322

This is just a few dBs shy of state of the art.

Good news continued into linearity measurement:
View attachment 40323

And jitter & noise measurements:
View attachment 40324

The low noise floor gave the S2 a leg up in the IMD versus level in the noise-dominated portion of that graph (sloping down):
View attachment 40325

As levels increase though, distortion takes over.

ESS DAC implementations tend to have a mid-level bump up in the above measurements. Manufacturers have lately been able to conquer that. Interesting that the S2 despite being an older design, is completely clear of that issue. So the secret was known earlier among some designers.

Multitone results are more hopeful than SINAD:
View attachment 40326

THD+N versus frequency swings back to disappointing side of the fence:
View attachment 40327

Filter response is standard affair:
View attachment 40331

Distortion Compensation
Turning off distortion compensation reduces performance substantially:
View attachment 40330

Can't imagine why you would want to turn this feature off.

Headphone Amplifier Measurements
Let's start with our noise measurement at just 50 milivolts to see if the quiet DAC noise floor shows up here:
View attachment 40328

Looks like the eye was taken off the ball here:
View attachment 40329

Sensitive IEMs will likely have some amount of background hiss at elevated volumes.

Power into high impedance load of 300 ohm is quite low:
View attachment 40332

Yet again we see elevated noise levels. The headphone amp is definitely noisier than the DAC portion.

Ditto for 33 ohm load:
View attachment 40333

This is very low power level. Hard to imagine a desktop product shipping with such low output level.

I thought maybe output impedance is high but it is not (thankfully):
View attachment 40335

Listening Tests
Not feeling good so I skipped listening to the S2. The numbers speak to inability to reach any decent level of loudness without distortion.

Conclusions
There are some really bright areas in performance of Pre Box S2. Its DAC has excellent noise floor, great accuracy in the form of linearity, and very low jitter. Distortion is high though for the class. That may not be an audible thing but the very low output levels of the headphone amplifier certainly is.

There are many good choices in this price range and lower so I can't recommend the Project Pre Box S2. But if you find a used one, pair it with a good headphone amplifier and you would be good to go.

--------
As always, questions, comments, corrections, etc. are welcome.

Was not feeling good per above and went to the doctor. He said I have MSD. I asked him what that was and he said: Money Starvation Disease. I asked him for the cure, he said it would come in the form of donations form you all. Of course the son of a gun took more money from me, making my symptoms even worse! Please help dig me out of this disease by donating using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
Those interested can compare this with the Stereophile measurements <https://www.stereophile.com/content/pro-ject-pre-box-s2-digital-da-headphone-amplifier-measurements>.
I was pleasantly surprised by the Pro-Ject Pre Box S2 Digital. This tiny, inexpensive box offers almost state-of-the-art measured digital performance.
 

dkinric

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#15
How do Stereophile's and Amir's measurements compare? Are there any apples to apples tests where they got significantly differing results? It was difficult for me to tell.
 

AudioSceptic

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#16
How do Stereophile's and Amir's measurements compare? Are there any apples to apples tests where they got significantly differing results? It was difficult for me to tell.
I'm hoping that someone can help with this. The conclusions are somewhat different, and that includes the headphone amp (in the subjective section).

I have one of these BTW, and am pleased with it. I use it mainly to feed the main system but also find the headphone amp easily powerful enough into Grado SR80e and BeyerDynamic DT880 32Ω.
 
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#17
Get well soon @amirm
I wouldn't expose myself to a 60dB noise floor when ill either. There's only so much a stomach can take. Have some Apple dongles and turn up the tubes to stay warm or something.
 

VintageFlanker

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#19
In EU this device is being sold with a (low quality) switching power supply. But authors recommends to use an external linear supply.
That doesn't sound good to me...at all. Why a $400 gear shouldn't perform at its best with the stock PSU? If it does, then either the design or the price is wrong.
Could you try some with external power supply?
Like IMD vs level and output power at low impedance?
It shouldn't change anything to the headphones output. Specs is 68mW under 32ohms, which is pretty close to what @amirm got... Not to mention very weak.
I'm sorry for Pro-Ject, but this unit is now outclassed by the similarly-priced M500, in every category.
 

bequietjk

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#20
What? An interesting price? 400$ for basically just the DAC (even with the external power, HP out would not give that much more) is interesting? You would freak out of Topping D10 then, less than 1/4 S2's price.
Not just that, DX3 Pro would be more than twice the AiO device for 1/2 of the price compared to this S2.
What's interesting to me is the quirky fun looks along with a mid level SINAD. Additionally, we have an excellent, low jitter noise floor, great linearity and the focus of performance is all over the place.

I would love to see this designer create something for us in the future. They certainly have the potential to produce something that can turn heads in this forum.
 
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