[sdiy] Signals leaking into the PSU?

[Mike Bryant]

Sorry Brian, and it may just be the way I've read what you've written, but that's not quite true.

There are numerous papers, often with opposing views, but the ones I read as being more interested in safety, as opposed to a best audio performance, are here :
https://www.ranecommercial.com/legacy/note110.html
https://www.ranecommercial.com/legacy/note151.html
and then expanded in some of their other papers.

One key sentence is "First let's examine why they must be tied together. We'll cover where and how in a moment." along with numerous references to "grounded".

Also in the UK, and some other countries, the wiring regulations require a mains ground connected to the frame of any 19" rack mount as it's currently classified as IT equipment.  Yes I know Behringer and others are selling their racks with a 2-pin class II PSU and this is in the queue for discussion in the relevant sub-committee when time permits as obviously the regulations may require change, but currently the official line is the frame should always be grounded (in the UK).

That's not to say how mains and audio grounds are connected, it's the big question mark in the Rane paper and they cover various scenarios.

There is also the case that the most popular PSUs used in DIY synths is class I and so mains ground has to be tied to signal ground.  Lifting that ground is illegal in most countries.

But as you say, how things are grounded must always be considered properly from the beginning, not tacked on at the end.

________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of brianw <brianw at audiobanshee.com>
Sent: 19 February 2023 19:32
To: Peter Knoot <peter at synquanon.com>
Cc: A.M. Barrio via Synth-diy <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Signals leaking into the PSU?

As a public service announcement, I would like to stress that the "wall socket ground" is for safety. It should never affect the signal noise, and circuit designers should never create anything that ties signal to the wall socket ground. I'm talking about the third pin on three-prong wall sockets.

I looked at the page in the provided link, which is a huge text, and found that it references Bill Whitlock and his papers on signals, grounding, and safety. I stress that folks should read Bill Whitlock's papers before designing anything that connects to wall socket ground.

Brian Willoughby


On Feb 19, 2023, at 8:45 AM, Peter Knoot wrote:
> This is actually quite a common issue.  The advice given so far is sound; bypass capacitors are certainly a must, but not sufficient solution.  A comprehensive approach must be taken for any Eurorack case (which tends to be far noisier than standalone equipment) to become noise-free.
>
> Proper filtering requires a good, low impedance ground path.  This includes the module circuitry (proper PCB layout practices), power distribution bus boards, power supply and of course the wall socket ground!  Many folks don't even consider the latter.
>
> Here's a great white paper by Genus Modu to give you some idea:
>
> http://www.genusmodu.com/products/libb-wp-01.html
>

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