MOTM

Paul wrote:

> 2) Filter design *slowy* in the background (2% bandwidth allocation).
> Hope to have time this month to finish the breadboard: needs to have
> good "Moog-ness" and a quiet pre-amp. Adding several bells & whistles
> to the env follower.

Here's a question for Moog experts:

I've heard that there were several versions of the ladder filter, and also
heard that the modular version sounded much clearer and more airy than the
MiniMoog, for instance. Anyone know about the different versions, and if the
modular version indeed sounds better?

Paul, do you have any thoughts yet on how your design will differ or
resemble any of the actual Moog versions?

Dave Bradley
Principal Software Engineer
Engineering Animation, Inc.
daveb@...

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