[sdiy] moog high pass flter

[harrybissell]

Hi Grant....

The PAiA 2720 was a "compound filter" of non-resonant LPF and BPF... for a
totally different reason.

I'll probably do another take on the Moog 904, maybe with SVF filters this time.

Does anyone have the Moog Satellite filter schem... I'd like to see that (just
when you thought you'd seen everything....)

H^) harry

btw... if you are really running a MAC with all those anti-virus proggies then
how
come you're sending us all viruses ??  (just kidding of course...)  ;^P

Grant Richter wrote:

> FWIW, you comment knocked a few loose nuts out of the junk pile...
>
> The Buchla 200 doesn't have a resonant lowpass filter. At first I thought
> Don just didn't like resonant filters, then I realized he designed it to
> synthesize a resonant lowpass by putting a tracking 291 bandpass in parallel
> with the 292 lowpass and synthesizing the resonant "hump" with the bandpass.
>
> So we could call it a "compound" filter where the total response is a
> product of two or more filters in series or parallel.
>
> The Moog 904 A,B and C is compound filter where the filter coupler is used
> to place the lowpass and highpass in series or parallel to form bandpass or
> band reject filters.
>
> The ARP Odyssey is a compound filter with the 24 dB/Oct lowpass followed by
> a passive highpass.
>
> The Moog "Satellite" synth has a compound filter composed of a state
> variable and a 12 dB/Oct transistor ladder lowpass.
>
> In your typical exponential converter, one of the transistor bases is
> grounded while the other is modulated with the 18 mv/Oct voltage. Jurgen and
> I have both played with expo converters where the transistors are "stacked"
> and the individual base voltages modulated to give offsets from the common
> input. In a 4 pole lowpass this allows you to slide the other poles around
> to give variable slope rolloff.
>
> A "real" compound filter would have a common exponential input with variable
> offset for each filter section. Then each section could be set to lowpass,
> bandpass or highpass and the sections switched into either series or
> parallel routing.
>
> I'm sure someone has already done this and is just waiting to show us the
> schematics ;^)