Definitive earthing advice sought.

[AndrewT]

Hi,

Originally posted by falcott
a) the grounding should be positioned in the centre of the amp chassis, or that

b) the grounding should be centred between the 2 amp boards (in the case of a stereo amp) if they are off-centre of the chassis?

I think that precise location does not matter.
Since it is floating "chassis" is irrelevant.

I would be tempted to keep it between the pair of amp modules but close to the PSU.

However, I believe a much more important issue is keeping the LOOP AREA of the PSU cables VERY SMALL. Those are the cables forming the centre tap, the two AC cables to the rectifier, the two +v & -ve cables to the PCB. But some PCBs have well separated PSU & Power ground input connections. The designer is either very clever or has not recognised the relevance of small loop area and the impulsive magnetic fileds coming from single cables.

[CarlosT]

Obviously twisting grounds together (PG- and PG+) helps? Does twisting any other specific set of wires help?

Luckily I got some cool twist pliers from my motorcyle trackday tool box

[AndrewT]

Hi,
when two cables carry the same current but in opposite directions then close coupling them will attenuate the magnetic field. Twisting achieves an extra measure of attenuation.

So, any pair that carry equal and opposite currents can be twisted.
Transformer psuedo centre tap.
Transformer AC to rectifier.
Rectifier to smoothing caps.
Loudspeaker to PCB, but don't connect the return. It goes to audio ground.
smoothing caps +ve & -ve AND 0v to PCB.
note: that last one NEEDS the 0v wire to make a threesome. The currents in the threesome cancel but not in any pair from the three.

A warning on the Loudspeaker suggestion.
The single return passing near the PCB on it's way to the audio ground may be worse than the line led to speaker terminal and then return from terminal led straight to audio ground.