If you have different circuit stages grounded on a common line, the resultant earth jacking can cause additive or subtractive valid signal production - this can cause a transient limiting/foldback characteristic, or a flaring/blapping characteristic according to stage earthing order and behaviour.
Intelligent placing/ordering of these interactive earths can give a desirable envelope response, and give voice to an amplifier system.
mrfeedback said:Hi MR,
In years of servicing audio gear I have seen all sorts of dumb wiring and pcb layout arrangements.
This includes doubtful power supply, preamp and power amp supply and grounding layouts, and other errors like taking NFB from an invalid (wrong) point.
I think it is not so much intentional as lacking of knowledge on the designers part.
Some munufacturers do however very deliberately adhere to star grounding of all stages, particularly in modern higher quality shelf systems.
A common error is an inadequate size pcb trace ground common connecting the two main filter caps.
Other errors include grounding stages to the speaker earth return traces.
A close look at the layout and intelligent rerouting and/or beefing up of some pcb traces can yield worthwhile improvement.
Bypassing of main filter caps with additional SMPS electros of around 10% of the main caps is usually a wortwhile improvement also.
Star grounding means that you have a substantial copper area connecting the two main filter caps, and this is the system earth reference to which all stages and input and output connectors are individually connected.