[sdiy] Eurorack Grounding Question

[Brian Willoughby]

On Dec 29, 2020, at 01:30, Steven Cook wrote:
> Hi, I'm designing a Eurorack module which uses a microcontroller. The PCB has separate analogue and digital grounds joined at the power input header, but I've realised since designing it that both grounds will also be shorted together by the front panel as there are input jacks connected to the digital ground and output jacks connected to the analogue ground. I assume this would create an ground loop. Would I be better off not bothering with separate grounds?

Why do you have "digital" signals on the front panel? Aren't they all analog signals? Maybe you have a USB jack on the front.

There are a few papers stating that separate grounds are pointless. Not everyone agrees on that. Perhaps the valid point is that it's still possible to do a bad job, even with separate grounds. I happen to think it's worth separating analog and digital, but you have to be really careful not to let signals cross ground planes because that's one way things can go wrong.


On Dec 29, 2020, at 01:38, Tony Allgood wrote:
> Create a third 0V connection (ground) from the power cable for the panel, pot brackets and sleeve connections on all sockets. Don't use this for anything else.

Tony has the best advice. If you have a star connection for the various "ground" nodes, then there hopefully won't be any noise crosstalk between them. Keep them all separate until the point on the PCB where the power cable grounds them all.

Consider this third 0V node to be "shield" rather than "ground" - maybe even use the "chassis" symbol to keep it separate from signal ground and power ground.

When you connect "chassis" to "ground" you can use a high resistance in parallel with a capacitor. This will keep the shield near 0V without conducting noise into signal and power. I typically use 1 MΩ in parallel with 0.1 µF. I tried using an inductor, but had poor results with that approach.

Brian Willoughby