[sdiy] Filter Not so strangeness

[James Patchell]

I think you are getting the 2720 Low Pass Filter and the 2720 Band pass 
filter confused.  The band pass filter had a pot  in series with the 
emmitter bypass cap, although, what that did was control the gain of the 
transistor that provided amplification.  The band pass filter used a twin T 
filter in the feedback loop of a single stage transistor amplifier....


At 09:23 AM 7/31/2004 -0500, Pat Kammerer wrote:
>Well,
>
>I ditched the sallen key filter I was working on, mainly because I had made
>just couple more mistake than I felt like fixing.  : )  So I've been looking
>around at different designs.
>
>I've thrown together a PAIA 2720 VCLF  (I know...), and I love the sound,
>much stronger and less noisy than the other. It also seems to like single
>polarity supply.
>
>http://www.muzique.com/schem/2720-3l.gif
>
>My question now is to anyone who may have built this into a module or
>whatever;
>
>I've read that to control resonance in this circuit you need a pot in series
>with the bypass capacitor that is across the emitter resistor.  I don't see
>this cap in the schematic unless I'm misunderstanding the word across  (?!)
>Or is the bypass cap the one at the supply input (100uf)?  I would like this
>option as it would make the sound much more versatile.  Theoretically,
>instead of voltage control for cutoff I could use a varying resistance from
>the two .05p caps to ground right, since the voltage creates a varying
>restance using the 1n914's?
>
>Fun simple circuit though.
>
>Thanks for your help

         -Jim
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