Update: Ordered a 12V wall wart described as "linear" and the noise is unchanged. Went through a drawer of wall warts and tried ~8 with no luck.

Decided to find one with screws in the case and see about bypassing the electronics so it would just be AC output from the transformer, then see about running that through a rectifier and regulators as needed. But the one I opened looked like this:


Looks like stepped down AC output goes to four diodes and a filter cap. Am I missing something or is this the basics of a linear supply? Because when I put it back together and plug it in, I still get the noise.

This is aging me.

 

Am I missing something or is this the basics of a linear supply?

That looks like a basic linear supply without regulation.
Is this powering the amp and what is the power source for the BT?

 

Update: Ordered a 12V wall wart described as "linear" and the noise is unchanged. Went through a drawer of wall warts and tried ~8 with no luck.

Decided to find one with screws in the case and see about bypassing the electronics so it would just be AC output from the transformer, then see about running that through a rectifier and regulators as needed. But the one I opened looked like this:
View attachment 348891

Looks like stepped down AC output goes to four diodes and a filter cap. Am I missing something or is this the basics of a linear supply? Because when I put it back together and plug it in, I still get the noise.

This is aging me.

Yup! That is the basic unregulated linear supply. The output voltage depends entirely on the load impedance. It is not uncommon for devices powered from wall warts to include additional voltage regulation circuitry.

 

With that single capacitor there is not much filtering. but there would be hum but no noise. So more filtering will be required.

 

MOST of the current five volt power supplies are switchers, and for battery charging not much filtering is required.
So if you have room for it, use an older type wall wart supply that has a transformer. Those are the heavy ones. With a higher voltage you can afford a bit of voltage drop in the filter, and then use a five volt linear IC regulator to provide a clean five volts. THAT should solve all of the noise issues.

The amp uses 12V and I've been trying a bench supply and a bunch of different wall warts to provide that, and a USB wart to power the bluetooth module. That works. But when I power a 5V regulator from the 12V for the bluetooth module (either a little board/module or a 7805), I get whine. I get it with the bench supply and with any of the 12V wall warts including the one I opened to confirm it's linear. I tried a wide variety of filter capacitor combinations on both the input and output of the 7805.

New plan. Setting aside the Yamaha speaker amp and trying a one-piece BT/amp module.

 

It seems to me, based on what I read now, that the whine must be intrinsic ti the bluetooth device. Is it possible to use a transformer to totally isolate the aidio output of the BT module from the amplifier circuit?? Bot signal and common (ground) sides?? It may also be that the BT device is simply noisy.