Re: [AH] MC-202 mods question

From Florian Anwander
Sent Tue, May 30th 2006, 08:29

Hi

> So anyone know how to do these? I'm thinking that the LFO mod involves having a lower value cap on a switch, 
Right. You may take over the idea Doepfer uses often: have two 
additional caps and a switch with middle position (no contact). This 
provides three ranges.

> but the filter mod I have no idea at this stage, so any help would be much appreciated.
I did not try this with the MC202, but the JX3P where I tested it, is 
quite similar:

Have a look at
  http://www.synthfool.com/schematics/mc202analog.gif
You will find the filter at position f9 to f13.

Add a 150k resistor (lets call it R148b) to pin 4 of IC27. Break up the 
connection betweeen the joining point R148/R147 and C67. Connect C67 to 
the toggle pin of a switch, whcih selects now between the  original 
connection (R147/R148) and the new R148b. You may of course use other 
stages of the Filter (pins 7 or 12).

This modding keeps the resonance at the 24dB output.

If you want to move the resonance feedback loop to the according stage 
you would have to breakup the connections to IC27/pin15 in that way, 
that pin15 and R154 stay connected and VR12 and R148 stay connected. 
Using other stages for the resonance requires perhaps to invert the 
resonance signal.

Florian