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Pro-Ject Pre Box S2 digital DAC

Discussion in 'audio' started by miero, May 9, 2017.

  1. sortof

    sortof Member

    How about adding a good linear PSU to the pre-box, would it improve soundquality?
     
  2. sam_cat

    sam_cat ʇɐɔ_ɯɐs

    Closest I could find:

    http://snvinyl.co.uk/Pro-Ject-Pre-Box-S2-Digital
     
  3. JohnW

    JohnW Trade: Lakewest

    Very much so - despite the effort we went to with the internal PSU, the external PSU makes a big difference.

    Pro-Ject have a Battery PSU for the DAC in the works.
     
  4. the_bat

    the_bat pfm Member

    Possibly silly question but does plugging headphones in mute the preamp output? The otherwise interesting Schiit Jutenheim and my very old Cyrus One don’t and it’s a real pain.
     
  5. JohnW

    JohnW Trade: Lakewest

    Yes, plugging in headphones mutes the main audio outputs.
     
  6. the_bat

    the_bat pfm Member

    Excellent. Thanks John.
     
  7. Rocketride

    Rocketride pfm Member

    JohnW, what is inside ProJect Pre Box S2Digital, your original design or ProJect's modification?
    Thanks!
     
  8. Baki

    Baki Active Member

    Two questions for JohnW:

    Are the analog outputs of the DAC chips directly connected to the RCA analog outputs?

    Are there coupling capacitors in the signal path?

    Thanks.
     
  9. JohnW

    JohnW Trade: Lakewest

    Are the analog outputs of the DAC chips directly connected to the RCA analog outputs?

    No - theres a buffer IC.

    Hell no!!! - DC coupled :)
     
  10. JohnW

    JohnW Trade: Lakewest

    Pictures I've seen have the correct capacitors fitted :)
     
  11. miero

    miero Member

    Just one small warning..

    I had to return this DAC, because it does not have a galvanic isolation of USB port and it did not work well in my crazy electric wiring setup. There has been noises from USB data transfers induced into speakers (whistling at 8kHz).

    I have a desktop PC with an ATX power supply and active monitors (Behringer B2031A) which have PE connected to GND. Those speakers were connected probably to a different circuit breaker, so the ground loop was very large and it behaved probably as an antenna.

    A workaround for this issue would be to connect the DAC using an USB High Speed isolator, but I don't want to invest more funds and time into this now.

    I'm attaching observations after day-two experience:
    - the DAC cannot be shut down, OLED is always lit
    - a menu/filter/input buttons with a cheap effect
    - box is heavier that it seems
    - there is a plastic remote control in a standard box (aluminum remote can be bought separately)
    - great sound with headphones
    - only a single filter for MQA files
    - "fake" samplerate is displayed for MQA files ... e.g. 352.8kHz instead of 44.1kHz
     
  12. Baki

    Baki Active Member

    Thank you John.

    I have already ordered one but the seller still did not receive the exact delivery date.

    Seems that demand currently exceeds the supply.
     
  13. Baki

    Baki Active Member

    John,

    What buffer IC is used?

    Thank you.
     
  14. gahabana

    gahabana Active Member

    my experience with "Pro-Ject Pre Box S2 digital DAC"

    Am using odroidxu4 (running Armbian builds of Ubuntu) as endpoint for Roon as well as LMS/squeezelite.
    Worked immediately with no issues.
    I also have a benchmark dac2 hgc (which i used both as preamp for pro-ject s2 and to compare).
    Love - all resolutions worked out of the box. PCM all the way to 768khz and DSD via DOP all the way to DSD256 with Roon.
    Sounds very good. Haven’t done a lot of critical listening - but i hear nothing worse compared to Benchmark DAC2. Remote (one that comes with it) is cheapo plastic bit bigger then credit card but works great for volume control and switching filters or on the fly or sources etc.
    sounds GREAT to me.
    things i love compared to Benchmark:

    switching between various sampling rate sources is practically instant. i.e. from 44.1khz CD to 192khz hires source or dsd is instant. on benchmark there was 0.4sec delay or you missed bit from start of the song. if all upsampled obviously none of the dac’s have issue with changing sampling rates but it makes me happy. i still use LMS from time to time so that comes in handy
    over 24+ hours no issues, clicks, losing sync etc … i think digital piece/USB is well implemented and has no obvious bugs …in spite of changing, reseting, roon and squeezelite - not once i had to reboot due to sw bug. that is great!!!. e.g. SMSL M9 DAC i also have works fine sounds good but when you reboot the pc or endpoint it starts with hiss until music app (roon or squeezelite) actually starts sending sometjhing (or even silence) … no big deal but bit annoying. as i am planning to replace benchmark dac2 with it and going directly to poweramp can not do that with SMSL m9 but think i ll have no issues with Pro-Ject S2
    it remembers volume setting upon power off … which is good if going to power amp directly
    MQA support - seems to work very well. 48 all the way to 192khz abd blue light works (tested with Roon/Tidal).
    downsides compared to benchmark:

    does not have balanced out’s that my amp has (Bryston) … can use RCAs but would be nice if it was balanced
    don’t care about headphones so did not compare at all
    it can not be powered off (if powered or connected via USB only and source is powered its always powered). not a big . deal … just would be nice if you could power it off
    has mute on remote just like benchmark … what benchmark also did is ‘Dim’ which takes volume 20 or 30db down so if you get a phone call can still hear the music but at much lower volume instantly … just cool
    i miss ability to power up amp via preamp/dac. it requires 12V output and i guess it did fit in benchmark and pro-ject bing 2-4 smaller box it kinda didn’t fit. if i switch to pro-ject and eliminate benchmark as a preamp ill have to turn on/off amplifier manually and cant do it via remote no more :frowning:
    i wish pro-ject would display sample rate and depth. behcmark does it with LEDs … and smsl has info screen. not that it matters cause it DOES work whatever you send to it (16/24/32 bit and any sample rate) …
    but benchmark is 2000EUR and Pro-ject 350. makes you wonder if its worth it.

    However, last step was to try S2 directly powering poweramp (Bryston SST2). All of the above still holds true however, there might be a problem for me to use it in that way unless you guys have some idea:
    Issue: when sample rate changes between the tracks very often i hear a farily loud click/pop between the tracks. I rebooted, powered off … changed settings in the DAC (filters and ‘distortion settings’ on or off) but that did not make any difference. i even inserted Intona isolater between by USB source computer and S2 just to be sure it’s not due to some ‘ground’ connection issues.

    My guess is that it could be fixed in the firmware of the S2 (whenever input sample rate changes drive output to 0 in few ms and that i think could do it) … it happens when going from 44.1 to 192 and any other mix … some combo’s almost every time some not so often. Of course if I upsample all the content from Roon to 352 or 384 kHZ it is a non issue but then MQA support is gone etc.

    I have no clue why i did not hear those clicks/pops when S2 was connected to Benchmark DAC2 which acted as pre-amplifier.

    Any thoughts/ideas ?

    Thanks !!!
     
  15. Julf

    Julf Evil brother of Mark V Shaney

    As I keep pointing out, you get most of the benefits of a balanced connection as long as the amp input is balanced / differential, and you use a cable with a RCA at one end, but wired as a differential (2 + shield) from the RCA connector on.
     
  16. gahabana

    gahabana Active Member

    hi Julf, yes you are right - will do that in the future, but i doubt that would eliminate the pops/clicks ?
     
  17. Julf

    Julf Evil brother of Mark V Shaney

    I agree, the cable is unlikely to have anything to do with the pops and clicks. If you get them with one amp, but not with another, I would suspect a DC offset on the DAC output (that one amp is sensitive to, but the other isn't). Maybe worth trying with a capacitor to decouple DC?
     
  18. gahabana

    gahabana Active Member

    yeah i suspect that can be only explanation (DC offset) ... i tried headphone output in the meantime ... still can hear pops/clicks though they are more quiet then music being played so it does not create a big problem. however, i don't like the idea of opening brand new DAC and soldering some extra (i guess it would need to be few micro-farads high quality capacitor) and i think JohnW mentioned it's DC coupled so adding it at the end would beat the purpose.

    Does anyone know if that is something that could be addressed by (future) firmware upgrade ? i.e. if DAC has left some offset in the output it could be taken to 0 via SW.

    ? who knows ...
     
  19. Julf

    Julf Evil brother of Mark V Shaney

    OK, both the DAC and your amp being DC coupled would explain it. One of them should have the capacitor, unless you can guarantee the DAC never puts out any DC. You can of course put the caps on the cable (or connector) if you don't want to solder the DAC or amp.

    Depends on where the DC is coming from. If it is digital, it can be fixed in software. If it is the analog output stage, then the actual DC will vary, and is hard to compensate out in software.
     
  20. gahabana

    gahabana Active Member

    thank you @Julf - i think you are right.
    I'm far from being electronics expert so can not judge. Though i do have degree in computer engineering and did have basic electronics classes that was almost 30 years ago and if you don't use something - it disappears. Anyhow, i did take a look at Bryston 4B-SST2 schematics ... if i can still read schematics partially well it does show 68microfarads that input signal is going through ... not sure if that one is supposed to block DC but my guess is yes ... here is the portion of the schematic : [​IMG] https://imgur.com/00mhE5Q
    Original schematic is at : http://bryston.com/PDF/Schematics/4BSST2_SCHEMATICS.pdf

    opinions ?
     

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