> if you think the component placement is important I can send
> the pcb picture/drawing (even I put it in the way that unregulated
> / unfiltered traces will not be near the audio circuit)

Audio should be kept away from any AC waves or ripple. Big
fat ground and power traces may help, and you may need to
augment them with bare wire soldered to them. Also a common
0V point is desirable. If all 0V lines go back to this common
point that can help eliminate grounding imbalances. This includes
the frame of the transformer too. Some transformers are enclosed
in a mild steel shell, but I don't know if that stops a lot of hum. If
you continue to experience real problems, you might try the
opposite - enclose the high gain section of the audio in a grounded
metal box

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