[sdiy] BPF w/VC bandwidth, depth?

[mark verbos]

what you are looking for is a bandpass filter like the Buchla 291. Then 
a 2 stage mixer section. The dry signal goes into the non-inverting 
input of the mixer. The output of the filter goes through a pot that 
controls if the output goes to the inverting or the non-inverting input 
of the mixer section. The gain of the mixer section will control how 
much cut/boost you get. Now to make a voltage controlled boost/cut (like 
you want) you need to use a voltage controlled panner to control if the 
output of the filter goes to the inverting or the non-inverting input. 
Does that make sense?

You mix the dry and the filtered together. keep it in phse to boost the 
filtered part and out of phse to cut it. The Buchla 291 (or any other 
design like it) gives you voltage control of frequency and bandwidth. 
PLUS it sweeps a very wide range with these controls, much wider than a 
conventional EQ would.

good luck

mark

David Cornutt wrote:

> OK, I'm sitting here looking at my parametric EQ (an old but still
> serviceable Furman), and the thought occurs to me:
>
> Is there any such thing as a voltage-controlled bandpass filter in which
> all three parameters of the filter -- center frequency, bandwidth, and
> boost/cut -- are independently voltage-controlled?  Any thoughts on
> how to build such a beast?  I'm afraid this goes way beyond the little
> bit of filter theory I know.
>
>