Doepfer

Hi

 > the a121
> highpass is somehow strange when putting to low frequencies (more
> like 
> bandpass), 

This is a known problem of this chip and it is described in the service 
manual of the A100:

You have two possibilities with the circuit:
  either to have a controllable resonance behaviour for the price of a 
littlebit limited hipass characteristics

  or to have a perfect hipass characterics but uncontrollable and 
unstopable selfoscillation when the cutoff frequencey became once quite 
high.


This is not a fault of Doepfers module, but a problem of all 
Multimodefilters that use the CEM3320.


Florian


btw:
I only can recommend to buy the service manual. It contains a lot of 
explanations and tips!