On 3/7/08, Richard Brewster put forth:
>There is no op amp in the 490. It is a Moog 904A emulator, all
>transistors, with a dual OTA output buffer. In the theory of operation,
>Paul Schreiber wrote, "A passive mixer is used to mimic the loading
>effects of the 904A filter...". Is the lower output level of the 490
>really a problem? It's still much higher, I believe, than the output of
>a real 904A. It works fine for me, as is.
As far as I can tell, it's the input level, not the ouput level.
The problem is best demonstrated by setting the filter for minimum
effect -- turning the resonance all the way down, and the frequency
all the way up -- it sounds like it cuts the input level by half. As
one would expect, adding resonance further lowers the input signal.
It says in the manual that "the output of the MOTM-490 is about 6Vpp
with a single 10Vpp input". I realize that it is designed so that
you can plug two VCO's into it without clipping, but with one VCO the
level seems too low. And it seems unusably low if I plug another
synth or drum machine into it. I don't have that problem with the
410, 440, etc.
I wonder how much those loading effects have an effect on the sound,
other than amplitude, as I don't see the difference between putting
an input op-amp in the module and connecting that input to the output
amp of some other module with a patch cord. The path is still op-amp
buffer/passive voltage divider/coupling cap.