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Grounding issues - any experts?

Discussion in 'audio' started by Dougunn, Jan 15, 2020.

  1. Dougunn

    Dougunn pfm Member

    Going a bit crazy here, any help gratefully received . . .

    I have a miniDSP DDRC22D Digital box that provides Dirac processing in my system. It is connected between a Raspberry PI with Allo Digione Signature and a Benchmark DAC2 by coaxial cables (from Mark Grant). The RPI and its Allo board are powered by dedicated linear powersupply. The DDRC22D is powered by a simple wall wart PSU all connected to a Tacima mains block (with surge protection and noise suppression).

    Unfortunately whenever I operate most electrical switches in my flat (lights, heating, cooker etc) the audio will cut out momentarily. The worst example of this is starting a fluorescent lamp which interrupts the audio significantly. If I take the DDRC22D out of the system everything works fine. I have been in touch with mini DSP who initially suggested switching out the IO board which I did (out of warranty) to no avail. They have now suggested that the problem is likely a grounding issue. Presumably RFI from nearby switches being picked up and momentarily screwing up the datastream?

    I am however a bit lost as to how to remedy this - although I suspect there still might be a hardware fault in the DDRC22D as, when I first obtained it (over a year ago), it it worked fine.

    The chassis on my Benchmark DAC is connected to earth but the DDRC22D and RPI are not. As an experiment I connected the ground of the unused RCA connector on the RPI to earth (so that the cable shields from the RPI to the DAC (via the DDRC22D) and the chassis of the DDRC22D itself were all grounded) and the system stopped working!

    I'm now stumped, but must confess I am a little unclear on grounding in this context.

    Any electrical experts out there who can give me a steer or suggestion as I really like what DIRAC does but the constant dropping out is not tolerable.

    Doug
     
  2. Shadders

    Shadders pfm Member

    Hi,
    Simple question - does the wall wart powering the DDRC22D, have an earth pin which conducts ?

    What is the power rating of the wall wart and the power requirements of the miniDSP ?

    Regards,
    Shadders.
     
  3. Dougunn

    Dougunn pfm Member

    The wall wart has a non conductive earth pin - its 5v 2000mA. It connects to the MiniDSP by a simple two pole barrel connector so no provision for earth to chassis etc.

    I've also tried powering it from the LPSU (swapping the wall wart to the RPI) no difference.

    Doug
     
  4. Shadders

    Shadders pfm Member

    Hi,
    Have you tried connecting the units with optical cables where possible ?.

    Also, the Allo Digione Signature has two power inputs, so are you powering these with separate power supplies as they suggest, and are the power supplies adequate ?.

    When it worked when you bought it (miniDSP), have you added anything since such as the Allo Digione Signature ?

    I see no reason for using a linear power supply for the RPI. Do you have the original power supply which will be a wall wart type ?

    Regards,
    Shadders.
     
    Julf likes this.
  5. starbuck

    starbuck pfm Member

    How long are the coaxial cables you're using? Random suggestion but if your coaxial cables are the usual 1m-ish length, do you have a cable (even an RCA phono cable will do to test) of 3m or longer that you can try in their place? I experienced something similar with a CD/DAC combo previously with the freezer solenoid being the worst culprit for causing it for me, and a longer coaxial cable cured it.
     
  6. Dougunn

    Dougunn pfm Member

    The Digione Sig does not have optical connections (as they have high levels of jitter compared to SPDIF).

    Yes, the RPI and Digione are powered separately; actually the LPSU has two outputs so it does both. I have also tried a battery option for the 'clean' side plus a standard wall wart on the RPI but there was no improvement so I went back to the LPSU for both.

    I originally had a standard Digione and then upgraded to the signature. For a while (I can't remember how long , but many months) this was working fine and I'm not aware of any change that heralded the drop-out problem.
     
  7. Shadders

    Shadders pfm Member

    Hi,
    It seems the Allo Digione Signature is a superfluous piece of equipment when it comes to functionality. Try your setup without that piece of equipment connected. At the same time, try a wall wart on the RPI.

    Regards,
    Shadders.
     
    Julf likes this.
  8. Dougunn

    Dougunn pfm Member

    The RCA cables are short (0.6m) and purchased specifically for the job. They are high-quality screened cable (although the screen isn't grounded, hence my experiment with making it so).

    I do have some cheap as chips RCA patch cables I could try
     
  9. Dougunn

    Dougunn pfm Member

    Huh? The Digione Sig brought about a significant improvement in my system, it is also essential as it provides the SPDIF output to the MiniDSP.
     
  10. david ellwood

    david ellwood Kirabosi Kognoscente

    I’d start by isolating the source of the problem by trying a laptop as your source of digits or removing the dsp and seeing if these alternative setups suffer the same.

    might be worth checking your electrical installation to ensure your earth impedance is ok.

    The fact that the lights which are on a different breaker to the ring are a source of problems is a concern.
     
    Julf likes this.
  11. Shadders

    Shadders pfm Member

    Hi,
    Try and eliminate what the issue is caused by. Remove the Allo Digione Signature piece of equipment, as it does nothing other than claim to solve jitter.

    The jitter in your system will be defined by your last piece of equipment in the chain, which is the Benchmark DAC.

    Regards,
    Shadders.
     
  12. Dougunn

    Dougunn pfm Member

    Yes, I have already determined that if I remove the DSP the problem goes away. For what ever reason it IS the issue but I cannot determine quite why. It appears that it is more sensitive to the issue than my other components. Or it's faulty somehow.
     
  13. Julf

    Julf Facts are our friends

    Indeed. Start without any weird audiophile stuff like linear power supplies.
     
    Shadders likes this.
  14. Dougunn

    Dougunn pfm Member


    The Digione is designed to use a low noise power supply - battery or LPSU - for its output side, plus a second 'regular' SMPSU for the RPI. It works fine in this regard with the MiniDSP removed. Add in the MiniDSP and the problem appears, ergo something is up with the MiniDSP, but what? Does it need improved grounding somehow -and what could this be?
     
  15. Yomanze

    Yomanze pfm Member

    I’ve had issues when using a Tacima mains block, have you tried taking this out?
     
  16. Dougunn

    Dougunn pfm Member

    That's an idea, no I have not tried that.

    What was the issue you had?
     
  17. Shadders

    Shadders pfm Member

    Hi,
    You have eliminated the miniDSP and the problem goes away. It could be the interaction with the miniDSP and Allo Digione Signature that is the problem - so, if you eliminate the Allo Digione Signature, does the problem remain ?

    Regards,
    Shadders.
     
  18. Dougunn

    Dougunn pfm Member

    Ah! I see your point. Without the Digione my system wont actually work. I have no other way to create SPDIF output.

    I may have the old 'standard' Digione I could try . . .

    Hmmmm.
     
  19. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    That could be the problem then. Standard 75 Ohm TV coax is ideal for the job.
     
    Shadders likes this.
  20. Julf

    Julf Facts are our friends

    So it has poor power supply regulation?

    You say you are using coaxial cables without screen connectivity. That is where I would start - the screen is there not just to protect from EMF, but to carry earth currents.
     
    Shadders likes this.

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