Re: [AH] [REVIEW] MOTM-450 Fixed Filter Bank

From Paul Schreiber
Sent Fri, Oct 24th 2003, 09:32

Just a few comments on John's through review:

a) the filter bank does use more power than any other analog MOTM module, around 180ma. The
average MOTM module draws about 25ma. I could use lower power quad op amps, but they are 4X the
cost of the ones in there now.

b) the prototype tested is actually 'missing' 1 frequency band at 2100Hz. I ran out of pc board
space :)
But it will be included on the production module.

c) about the filter band labels: they are the same as the Moog 907, BUT....it turns out that Moog
didn't use the *center frequency* for his filter labels, he use the *lower 3dB point* on the
bandpass. I didn't realize this until too late. So, the production version will tweak the
capacitor/resistor values to shift all the filters down slightly to match the center frequency
with the label. This is how the .com and Doepfer did it, and this is what users expect. I will do
likewise.

d) the prototype gain is indeed set wrong for full 10V pk-pk VCO driving signals. I was using my
bench test signal generator and Audio Precision, both default set to 1V Pk-Pk. This is a 1
resistor tweak.

Paul S.