Quote:
Originally Posted by Grubhead
If the noise is still present on them it could be in the headphone amp part of the circuit.
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The head-phone output of this amp is taken directly from the speaker-outputs through 2 x 330-Ohm resistors.
This is not going to generate any noise so it must always be there and go unnoticed when using speakers only or the clearly unsuitable headphone used causes self-oscillation in the output amp. circuit.
The latter is, however not likely as the headphone is isolated from the outputs by the 330-Ohm resistors so even a dead short of the signal to ground is harmless.