Korg MS-20 filter module
1999-03-19 by Dave Bradley
Paul posted this to AH, has some good info on the Korg filter - not all of us are on AH, right? Paul sez: This will sound strange (pun alert!) but I suppose you will have to accept it on faith unless you buy one. We built the original MS-20 filter. We reversed the epoxy block (it had 6 transistors in it. Big deal) and built a perfect, exact clone. Next, we built basically the same filter topology using OTA gain cells instead of the 6 transistor gain cell Korg used. <<Donning flame suit>> WE LIKE THE OTA VERSION BETTER. The MS-20 "squeaky-ness" is due to non-constant Q with input amplitude. We SPICE'd the hell out of both circuits. We spent 2 weeks A/B ing them with a real MS-20. WE LIKE THE OTA VERSION BETTER. We added HP/LP/Notch response, exponential, temperature compensted CV, and variable +/- sweep response. Also added variable input overdrive with LED indicator. So: why do we think the OTA version is better? Answer: reduced CV feedthrough. The MS-20 with not-so-matched transistors has considerable CVF at bass frequencies. This causes "muddiness" and DC offsets. NO, I don't think this is "part of the unique MS-20 sound". This again is due to non-constant Q with input amplitude. This feature IS in the OTA version, EXACTLY as is the original. We feel the MOTM-420 capture the MS-20 "whispy grit" with MUCH better bottom end. Only 1 way to find out! No price yet, but I expect it to be around $130 kit $180 assembled. Also: in the MS-20 you have both a HP and a LP in series. The MOTM-420 is switchable to HP/LP/Notch. So, you are correct that to get the MS-20s exacy HP>>LP configuration you need 2 MOTM-420s set the same way. BUT: you then get HP>>HP, LP>>LP, LP>>HP, Notch>>LP, etc. Paul Schreiber Synthesis Technology >Paul Schreiber wrote: >>MOTM-420 MS-20 filter (with added Notch response) will start shipping in >>about 3 weeks. > >Is this a genuine, part-for-part, lifted from the schematic, genuine Korg >filter chip using copy (excepting the notch mixing components)? I'd buy >two if so. Please fill us in. > >Easier, > >Mike > Dave Bradley Principal Software Engineer Engineering Animation, Inc. daveb@...