27-08-2019, 04:52 PM
(27-08-2019, 01:11 PM)Mark Hennessy Wrote: Entirely grounding.Always been an issue. Audio, Instrumentation, Logic, PSUs.
One solution for non-PCB is the star approach, even if an earthed chassis or a PCB. Another is the heavy aluminium chassis, layout still matters. I had a Guitar amp here the other day with terrific hum. Painted steel chassis and the paint under some earth tags! Also earth return for an ECC85 grid via screened cable (reverb springline). A 470 K Ohm at the valve base cured that.
A third approach, common on USA radio sets, (isolated or transformerless) and some amps is buss-bar. But layout and connections in the right order are important.
A PCB doesn't magically make earth path and layout issues go away, even if it has a massive ground plane. The pulse currents between transformer / bridge / main smoothing cap must not flow anywhere else!
