This is like asking 50 people about beer. The #1 thing that people have determined is that the top and bottom pairs in the ladder need their Vbe voltages matched as close as possible. I am betting that Moog saved the "good stuff" for the modular. The Minimoog had over 15,000 built, versus probably 500-750 Moog 904s. So, just as a matter of "cranking them out", the matching (all done by hand with a 1970 voltmeter!) was sloppier on the Minis. Also, the #2 factor is the input impedance of the differential amplifier that 'taps' the signals off the ladder. (BTW: if this sounds like babbling, then head over to www.ibm.com/patents and download Moog's filter). In the MOTM-400, #1 is solved by 2 pre-matched (actually, laser-trimmed to *be matched*) transistors, and #2 in easily solved in today's world with FET input op amps. However, it's all subjective and I hope everyone will be happy with it. Paul Schreiber
Message
Re: Moog filter design (was VCO diving)
1999-02-10 by Paul Schreiber
Attachments
- No local attachments were found for this message.