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Pro-ject Phono Box DS2 USB Phono Stage Review

amirm

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#1
This is a review and detailed measurements of the Project Phono Box DS2 phono preamplifier with USB capture capability. It is kindly loaned to me by a member. The DS2 costs US $599 from their dealers.

It is hard to differentiate in looks of desktop products but I think Project pulls this off nicely with a modern, European look:

Phono Box DS2 USB Phono Amplifier USB capture Audio Review.jpg


A reassuring relay click is heard as you change gain settings that go form 40 to 65 dB in five steps. I only tested the 40 dB (ostensibly for moving magnet cartridges) and 65 dB (for moving coil).

Different than other phono preamplifiers is inclusion of USB capture:

Phono Box DS2 USB Phono Amplifier USB capture back panel inputs outputs Audio Review.jpg


You have the nice volume control to set the capture gain and choice of 48 kHz, 96 and 192 kHz PCM and DSD 128. I only tested the 48 kHz setting as otherwise you are likely just capture more noise.

A small external switching power supply generating 18 volts is used.

There is also a line in input so you can use the DS2 as a general purpose capture device for non-phono sources.

Overall, the job is well done as far as functionality and looks. Yeh, some VU meters would have been nice on the capture side but otherwise, good.

Phono Stage Measurements
Let's start by feeding the DS2 5 millivolt simulating a moving magnet cartridge using the 40 dB gain:

Phono Box DS2 USB Phono Amplifier USB Moving Magnet Measurements.png


Nice. We don't see any distortion product and performance is strictly dominated by the noise level giving us a nice SINAD of 80 dB, likely way better than the source it is dealing with (LP). We can measure the THD (minus noise) by itself:

Phono Box DS2 USB Phono Amplifier USB Moving Magnet Distortion Measurements.png


Very nice.

Frequency response shows good RIAA implementation:

Phono Box DS2 USB Phono Amplifier USB Moving Magnet Frequency Response Measurements.png


There is very good headroom for 40 dB gain but it shrinks significantly for 65 dB:

Phono Box DS2 USB Phono Amplifier USB THD+N vs Level headroom Measurements.png


Above is at 1 kHz. Running it at different frequencies shows that the headroom shrinks also when frequencies go up:

Phono Box DS2 USB Phono Amplifier USB THD+N vs Level vs Frequerncy headroom Measurements.png


Since LP ticks and pops are likely to be high frequency in nature, this is unfortunate.

At our nominal 5 millivolt input though, distortion+noise is not frequency dependent (likely because it is noise dominated) except at 20 Hz:

Phono Box DS2 USB Phono Amplifier USB Moving Magnet THD+N vs Frequency Measurements.png


USB Capture Measurements
You are paying good few dollars for USB capture feature so let's test that with phono input:

Phono Box DS2 USB Phono Amplifier USB capture Audio Measurements.png


This is not good. We have a bunch of distortion products and increase in low frequency noise, bring our SINAD down substantially.

As noted, even at max volume, I could not hit 0 dBFS which likely makes the noise performance worse.

Let's switch to line input to see what we get:

Phono Box DS2 USB Phono Amplifier USB capture Line In Audio Measurements.png


Wow, that is quite a bit of distortion. Very disappointing. Needless to say, ranking is at the bottom of the audio interfaces we have tested:
Best sound capture card USB interface.png


Dynamic range is decent though:

Phono Box DS2 USB Phono Amplifier USB capture Line In Dynamic Range Audio Measurements.png


Conclusions
Project has designed an attractive package with nice functionality in DS2. Analog performance keeps up producing very low distortion and good low noise performance.

Sadly the digital section seems to be an afterthought, not matching the performance of the analog section. You can come out way ahead by using another interface instead of the one built-in. Then again you will be paying for functionality you won't be using.

Overall, I like the look and basic analog performance of PRoject Phono Box DS2 USB and on that basis alone, I am going to recommend it. But personally I would not pay that much for it.

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LTig

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#2
The performance of the ADC is strange. Surely it can't be so difficult to design one which is better than the preamp.

The frequency dependency of headroom is totally unexpected. Due to the characteristic of the RIAA curve headroom at high frequencies should be much higher than at low frequencies (40 dB more gain at 20 Hz compared to 20 kHz).
 

DDF

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#4
Nice box but it does pose a risk of digital overload.

Assuming they define "gain" using standard analog<->dBFS level translation, the minimum 40 dB gain can overload the digital output and create nasty clipping distortion.

Here's an analysis attached with my cartridge, phono pre-amp and A/D with USB out. With 37 dB gain, I had some records (12" 45rpms) that overloaded in the digital domain with hard clipping, as predicted by the worst case LP groove amplitudes shown. I added 10 dB loss on the output of my phono pre (taking gain down to 27dB) and that seemed to fix it.
 

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SimpleTheater

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#6
Our garden is finally producing lots of vegetables and fruit. So don't need your money for that. But do need it to buy meat and fish to go with it.
Marketing tip. Ask for money after giving a headless panther to a major new product.
 

Soniclife

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#7
You have the nice volume control to set the capture gain and choice of 48 kHz, 96 and 192 kHz PCM and DSD 128. I only tested the 48 kHz setting as otherwise you are likely just capture more noise.
Is it not worth testing the other rates as 48khz is so oddly poor?
 

DDF

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#8
That's what the knob on the front is for.
Yes, agree. However if volume is just for digital capture, it would still apply for the use case of a separate A/D per post #3.

@amirm, suggest checking out the analysis in post #4 for helping set dynamic range targets for your phono pre measures. The groove data wasn't easy to come by, please PM me if you want the excel file.
 

franspambot

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#9
I own this. Anyone want to recommend an effective, A/D stage that can take the place of the USB output on this?
Check the ADC list mentioned in the review. I would add the miniDSP SHD, which I use to great effect for both listening to and recording LPs. The bonus is that with it you can take advantage of DSP.

Oh, and, great record!
 

JohnYang1997

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#10
Can someone please educate me on why we always have a very down sloping noise floor for all phono preamps? RIAA inverse filter related?
What's the highest possible ideal performance of a phono preamp with AP?
 
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amirm

amirm

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Thread Starter #11
Can someone please educate me on why we always have a very down sloping noise floor for all phono preamps? RIAA inverse filter related?
What's the highest possible ideal performance of a phono preamp with AP?
RIAA filter in the phono preamp naturally does that. For my sweeps I use the inverse RIAA in the generator. Naturally that doesn't do anything for a 1 kHz tone used in the dashboard so you see that kind of noise floor.
 

JohnYang1997

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#13
If max is 5.9mV at 65dB gain, that's higher than 25dB less than 89mV at 40dB gain, so that's pretty much the same, isn't it ?
That's input referred headroom. The clip and pop is the same amplitude at your input regardless of your gain setting. So you are much more likely to clip the preamp with 65dB gain. That's why.
 

JohnYang1997

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#16
Just did some measurements and simulations. The absolute best performance we can see on the AP with 5mV 1KHz output and 40dB gain is probably 0.003% THD+N or 90dB SINAD.
AP's equipment output noise 0.18uV 20KHz BW. 40dB gain after passive RIAA means 60dB amplification before the filter. The high frequency roll off does reduce some noise, so the best case output noise is 17uV. Hence if there's no distortion. The best case SINAD is 90dB.

The input inferred noise of this device is 0.45uV 20KHz BW. Not bad.
 
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JohnYang1997

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#18
Hi Amir
Does that mean that your actual generator output level is actually higher for high frequencies ?
If that's the case, isn't it expected to reach saturation earlier in highs ?
Yes it does as shown in this graph. That's caused by the process of filter being after the amplification. But you get best noise performance this way.
Phono Box DS2 USB Phono Amplifier USB THD+N vs Level vs Frequerncy headroom Measurements.png
 
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daftcombo

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#20
I own this. Anyone want to recommend an effective, A/D stage that can take the place of the USB output on this?
Focusrite Scarlett 4i4. Also does DAC.

Great review. Very disappointed about the USB performance. It might be sufficient for vinyl ripping tho.
 
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