• Registered: 2023-02-04
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Topic: ADI-2 dac Fs ground loop

Hello I’m having a bit of an issue with a low 50/60 cycle hum through subwoofer and studio monitors
Signal chain is blue sound node coaxial to adi-2 dac then out via xlr to presonus subwoofer and to dynaudio Lyd5 monitors via xlr. Things I’ve tried are swapping to usb to dac no change, lifted pin 1 on xlr plug from dac but this made hum a lot louder. Hum is still present with dac turned off in standby
No hum through phones only when connected into monitors. Monitors don’t hum through different Dac (Cambridge audio Dac magic plus)
Any ideas

2 Reply by KaiS (edited by KaiS 2023-02-04 18:38:49)

  • KaiS
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Re: ADI-2 dac Fs ground loop

Some things to try:

• Use Digital Optical instead of Coax.

• Temporarily bypass the sub by unplugging and direct connecting of the XLR’s.
If this helps, the sub is in fact unbalanced and needs a balancing adapter.

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  • Registered: 2023-02-04
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Re: ADI-2 dac Fs ground loop

Thanks just tried optical and same hum. I will take the sub out of the chain and see
It a presonus t8 sub so not sure if it is fully balanced but it’s ok using xlr out of the Cambridge dac

4 Reply by KaiS (edited by KaiS 2023-02-04 18:50:05)

  • KaiS
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Re: ADI-2 dac Fs ground loop

darren.e wrote:

Thanks just tried optical and same hum. I will take the sub out of the chain and see
It a presonus t8 sub so not sure if it is fully balanced but it’s ok using xlr out of the Cambridge dac

Did you maybe use (unbalanced) TS instead of (balanced) TRS plugs for the sub?
- And real balanced - 2 wires + shield - cables all through?

With true balanced interconnects no hum should appear.

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  • Registered: 2023-02-04
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Re: ADI-2 dac Fs ground loop

Yes they are balanced xlr to trs cables with shield connected at both ends. I tried lifting the shield on 1 end and it made the noise worse.

6 Reply by KaiS (edited by KaiS 2023-02-05 11:00:34)

  • KaiS
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Re: ADI-2 dac Fs ground loop

darren.e wrote:

Yes they are balanced xlr to trs cables with shield connected at both ends. I tried lifting the shield on 1 end and it made the noise worse.

Strange, with true balanced interconnects this may not happen.
Even lifting the shield would not change much.
Else recording studios wouldn‘t work.

There must be something wrong with the cables or the (sub?)-speaker inputs.

Are you sure no XLR Pin1-Pin3 or TRS Ring-Sleeve bridging is present anywhere?

Connection scheme is correct?
(Colors are exemplary):

XLR  TRS    Wire
Pin1 Sleeve Screen
Pin2 Tip    Red
Pin3 Ring   Blue

Do you have a continuity tester to positively check?

KaiS's Website

  • Registered: 2023-02-04
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Re: ADI-2 dac Fs ground loop

Hi
Yep tried that this morning and got some strange readings on pin 1 on one of the cables. So connected one cable at a time and it hummed with one only. Long story short found a cold solder joint on the shield of the trs connector. Reflowed and all good now.
I may still ground the Dac case as I’m getting the slight hum from my lcd x when I touch them though
Thanks

8 Reply by KaiS (edited by KaiS 2023-02-05 14:04:57)

  • KaiS
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Re: ADI-2 dac Fs ground loop

darren.e wrote:

... found a cold solder joint on the shield of the trs connector. Reflowed and all good now.

Gratulations for fixing it.

darren.e wrote:

I may still ground the Dac case as I’m getting the slight hum from my lcd x when I touch them though

This is interesting, as there already should be an earth/ground connection through the safety earth of the Focal’s and Presonus’ mains connection, via the audio cable shield.

Which country are you living in, if I may ask?
Don’t you have safety earth in your mains power system?

Maybe your household is mis-wired, a serious safety hazard.

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  • Registered: 2023-02-04
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Re: ADI-2 dac Fs ground loop

Hi
I’m in Australia and I was thinking the same as you that now the grounds on the xlr cables are sorted so I just tested with headphones and the hum when touching the lcd x is gone as well. It’s now absolutely dead quite now.
Goes to show you can’t always trust factory made cables to be %100 all the time
Thanks for your help