Hi. A picture would be helpful.

The one ground you absolutely need is the power ground/Earth to the chassis.

Ground loops occur when you provide multiple paths for elections to flow to ground.

I personally like to keep my signal grounds (in low voltage applications like this) completely isolated from power grounds. I use isolated RCA input jacks, connecting them directly to the volume pot, then to the Ventus boards. If the boards share a ground, share it at the output of the power supply(s) and nowhere else. I would then route the Ventus outputs to isolated output RCA jacks.

Give that a try and see if you still have noise.


[EDIT]: It is also possible that one or both boards is missing it's signal ground (bad connection) which can also cause noise in single-ended setups.

Edited by user Monday, January 6, 2020 8:33:14 PM(UTC)  | Reason: Not specified

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Edited by user Thursday, February 13, 2020 3:58:42 AM(UTC)  | Reason: Not specified

First question: what is that filter board (with the caps)?

Second, one the board on the left, there is a signal ground at both input and output. The board on the right there is no signal ground. Where do these lead?

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Edited by user Thursday, February 13, 2020 3:59:13 AM(UTC)  | Reason: Not specified

Well that was a waste of 30 days.