Hi Dieter

> I cannot imagine a fault that causes distortion and that is not caused by
> the two integrated circuits. These are the only active parts in the module.
> Anyway - we will see what is wrong if the module comes back to us for
> service. Maybe the 1000u AC coupling capacitor in the amplifier output is
> defective. In any case the repair is covered by warranty.

I know funny distortions from opamps driven by an asymetric power
supply: Maybe a broken wire in the power ribbon cable, or cold/broken
solder joint at the bus connector of the module. Both could be caused by
the frequent removing of the module.

Florian