[JasonACT]

Oh, I forgot to add.. In my tests, I've connected a switch (no, not the big one) so I can hear old vs new-mods. There is identical hiss when I traced the speaker line back to the largest chip on the circuit board (clearly a sound processor - which has 4 raw speaker outputs) and used the recommended 0.22uF cap. for the AMP vs the numerous components (and there are a lot) on the board. Identical sound too when the volume is turned up. The hiss is either in or before that sound processor micro-chip.

I even connected up another AMP to one of those outputs and there's hiss, along with ground noise. There is no fixing this unit, only working around it, if I can get the attenuation circuit working.