[QUOTE=Jolly 7;1518878]
Quote:
Originally Posted by Al (astral highway)
Quote:
Originally Posted by Jolly 7
I think I'll try one of them instead to see if that gets rid of the noise problem. This is probably the easiest way for me. If it doesn't, it's back to the drawing board 😄
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.. the amplifier sounds great when feeding it with an audio source not powered by the same transformer e.g. an android tablet or battery operated radio. |
So that's a good start. It eliminates certain problems right away.
The problem is almost certainly to do with a) your grounding arrangements or b) something getting in the signal pathway when it shouldn't.
Effective grounding isn't as simple as which wires to connect to others.
Takes quite a lot of hands-on experience and examining successful builds of circuits to see how it's done. Same with diagnostic fault-finding.
It may be -- because you haven't demonstrated it otherwise yet -- that this is quite new terrain for you...
Afterthought. There's a really good reason why there aren't commercially available combined variable voltage power supplies in the same package as an audio amplifier.
It's a really bad idea! 
. If they did exist, they wouldn't be sharing the same transformer and they'd be completely isolated power supplies and there's be a lot of physical space and shielding between them.
But nothing ventured, nothing gained...
So, if you're open to some redesign ideas, which may include increasing the footprint of your assembly, it may be AOK in the end.