That wavering whistle sounds like what you can hear on an analogue radio. The datasheet for the class D amplifiers shows that they work at about 500kHz, and require all sorts of HF filtering to stop radiation. I doubt that electrolytics are to blame - more likely some small filter component.
Is the unit stereo? If so, is the noise coming from only one speaker?
I tried poking onto individual capacitors with a thin wire (where they're not too tiny to risk shorting-out) in the hope it would change the 'loading' of the components, and at least change the noise somehow, but that revealed nothing.
Yes, both.
it wouldn't
the only filter component that's likely to have gone bad is capacitors.
Yes, but not electrolytics.
I'm unlikely to change SMD caps ... the hot air rework wand on my solder station has only ever been used for heatshrink.
It's still half disassembled, is there a reasonable method to use a scope to track the noise down? it has a [slow] fft mode.
Essentially if the scope is sensitive enough you trace from the output backwards until the noise isn't there and replace the components immediately following. If the noise turns out to be RF based. start touching bits of the circuit to see what changes it. Rf instability is generally an open circuit cap.
Trouble is, each new variant of circuit throws up issues you never thought were possible.
I spent days tracking down noise in a valve amplifier never believing that the *output* valves themselves were at fault.
Then on another circuit a FET opamp in the middle of the board just went bad for no reason at all.
Years ago I had a power transistor fail with a base to emitter short. Normally the collector base punches through and shorts, but this one was unique. I never saw it before or since, so being a metal case I sawed the top off...and behold someone had spot welded the bond wire to the base badly off centre, and when it got hot it expanded enough to short to the emitter. You could see where a teeny arc had left a mark on the chip.
In many cases its not worth spending the time, unless you enjoy the challenge
Yes I tried that, because I thought I'd remembered it altering behaviour of circuits before, but someone else said touching it wouldn't help
Anyway all it changed for this amp was hum pickup
I thought about squeezing a replacement TPA3116 PCB in it, or gutting it to just the actual speakers and an external 2.1 amp, then I remembered an old set of powered PC speakers, they seem to be good enough and no annoying warble to keep me awake at night ...
shakes head
If you feed it with a sine wave source, it should be relatively easy enough to follow through the analogue stages looking at the waveform on the scope and seeing where the noise is creeping in.
I don't have a signal generator as such, but could generate a sine wave in audacity and pipe lineout to the amp ...
50hz is fine
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