Doepfer

Hi folks, I have two A-199's. One new, which is perfect, and the other 
used, which has an audible buzz at mix levels above about 40%. The 
same buzz exists in both modules (and sounds like 
excessive "emphasis"), but to a far lesser extent in the new one. The 
old one tends to bang the springs around more too, as though the 
default gain is much higher. So the question is, is this normal? Has 
the A-199 been improved so that it is now quieter than it used to be? 
Has the gain level been changed? If not, any suggestions on repairing 
(or possible grounding issue)? 

Oh, it occurs to me now that I had intended to swap the tanks to see 
if the problem is there, but I haven't done that yet.

Thanks,
Doug