This is a review and detailed measurements of the Pro-Ject Tube Box S2 phono preamplifier. It is on kind loan from a member. The S2 costs US $399 on Amazon including Prime shipping.
I must this say this is the cutest tube audio product I have seen:
A nice set of controls let you pick one of six (6) different gains plus a useful subsonic filter.
Power is provided through an external switcher, a bit larger than a typical USB charger:
Sorry, don't know what tube is in there. Perhaps the owner can chime in.
Phono Preamplifier Audio Measurements
My standard dashboard is a 1 kHz tone at 5 millivolts simulating a moving magnet cartridge. Here is the output with 40 dB gain setting:
SINAD is mainly determined by the "tube 2nd harmonic distortion" to the tune of -72 dB. Add a bit of noise to it and you arrive at our SINAD of 69 dB. This naturally ranks near the bottom of our rankings:
One of the most important tests of a phono preamplifier is the proper implementation of RIAA equalization and the S2 does well here:
Other than tiny bit of emphasis at low frequencies the rest is pretty flat. Subsonic filter (dashed purple) does what it is supposed to do to get run of LP rumble.
Signal to noise ratio is not great by our standards but likely better than what the format (LP) can do:
Distortion versus input level is again "tube like" with proportional rise and without hard clipping until the end:
Distortion+noise versus frequency shows good behavior:
It gets a bit upset at 20 Hz and rises a bit at highest frequencies. For the most sensitive part of our hearing (2 to 5 kHz), it is the lowest at -70 dB.
Conclusions
Most of the time when a tube is put in some audio product the result is a disaster. It is as if they think stuffing the tube in there is all they need to do, performance to be damned. Not here. The Pro-Ject Tube Box S2 seems to have been designed well to do what people expect a tube to do: produce a gradual rise in distortion with level.
Personally I have no use for a tube audio product. When I have listened to them in the past, they either do nothing (i.e. distortion is below audibility) or obscure detail due to higher distortion. To the extent you do, the Pro-ject Box S2 scratches that itch well and looks adorable to boot!
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As always, questions, comments, recommendations, etc. are welcome.
You all know how addicted I am to money and shopping. I thought I see if I can shake off the habit and stop buying things cold turkey. Well, it didn't last but a few hours before I went on Amazon and bought something!!! Can't help it. Until I figure out the method to kick the habit, I need to rely on your money. So please donate what you can using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
I must this say this is the cutest tube audio product I have seen:
A nice set of controls let you pick one of six (6) different gains plus a useful subsonic filter.
Power is provided through an external switcher, a bit larger than a typical USB charger:
Sorry, don't know what tube is in there. Perhaps the owner can chime in.
Phono Preamplifier Audio Measurements
My standard dashboard is a 1 kHz tone at 5 millivolts simulating a moving magnet cartridge. Here is the output with 40 dB gain setting:
SINAD is mainly determined by the "tube 2nd harmonic distortion" to the tune of -72 dB. Add a bit of noise to it and you arrive at our SINAD of 69 dB. This naturally ranks near the bottom of our rankings:
One of the most important tests of a phono preamplifier is the proper implementation of RIAA equalization and the S2 does well here:
Other than tiny bit of emphasis at low frequencies the rest is pretty flat. Subsonic filter (dashed purple) does what it is supposed to do to get run of LP rumble.
Signal to noise ratio is not great by our standards but likely better than what the format (LP) can do:
Distortion versus input level is again "tube like" with proportional rise and without hard clipping until the end:
Distortion+noise versus frequency shows good behavior:
It gets a bit upset at 20 Hz and rises a bit at highest frequencies. For the most sensitive part of our hearing (2 to 5 kHz), it is the lowest at -70 dB.
Conclusions
Most of the time when a tube is put in some audio product the result is a disaster. It is as if they think stuffing the tube in there is all they need to do, performance to be damned. Not here. The Pro-Ject Tube Box S2 seems to have been designed well to do what people expect a tube to do: produce a gradual rise in distortion with level.
Personally I have no use for a tube audio product. When I have listened to them in the past, they either do nothing (i.e. distortion is below audibility) or obscure detail due to higher distortion. To the extent you do, the Pro-ject Box S2 scratches that itch well and looks adorable to boot!
-----------
As always, questions, comments, recommendations, etc. are welcome.
You all know how addicted I am to money and shopping. I thought I see if I can shake off the habit and stop buying things cold turkey. Well, it didn't last but a few hours before I went on Amazon and bought something!!! Can't help it. Until I figure out the method to kick the habit, I need to rely on your money. So please donate what you can using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
