[sdiy] Buchla Lowpass Gate Switch

[Harry Bissell Jr]

Yep... the one cap is the .0047 when the switch is on
and the other is the .001

The 220pF and the 4.7M won't make too much difference
imho... but its a classic SK if you don't look at them
in the circuit.

H^) harry




--- Peter Grenader <peter at buzzclick-music.com> wrote:

> The 291 is Sallen & Key?  I never realized this. 
> I'm looking at the
> schematic now and still i can't see that
> configuration. Don's drawing
> coupled with my naivete?
> 
> Isn't the cap supposed to be across the amp in one
> of those??
> 
> 
> 
> bissell wrote:
> 
> > The S-K filter is absolute?y famous for severe
> interaction with the
> > input level...
> > especially in mid to high rez applications. 
> Personally I find it to be
> > a "touch tone
> > telephone" sound (before the FCP was invented
> :^)...
> > 
> > You might have even interfered with the overall Q
> of the S-K filter by
> > making those
> > resistances too radical.  Also possible that the
> mismatch between cells
> > caused an
> > artifact ???
> > 
> > One thing I can say for the LPG...   it has some
> amazing sounds for an
> > economy
> > of components !!!
> > 
> > H^) harry
> > 
> > Peter Grenader wrote:
> > 
> >> Well, I'll tell ya...My average signal strength
> in my system is
> >> somewhere around 7 volts. A Buchla's what - 2? 
> The thing was kazooing
> >> like a banchee in medium to high res
> configurations.  So, using a
> >> divider I dropped the amplitude at the input to 2
> volts, then brought
> >> it back up at the end with another op amp and
> .... problem gone.
> >> 
> >> 
> >> 
> >> 
> >> 
> >> I dropped the amplitu mark verbos wrote:
> >> 
> >> 
> >> I still think the distortion is from somewhere
> else in the
> >> circuit. Those op-amps have a fair amount of gain
> in the
> >> middle there. Especially at narrow bandwidths, I
> think you
> >> may have been railing them with your 10 volt
> signal.
> >> Remember that the circuit is intended for line
> level.
> >> 
> >> Mark
> >> 
> >> 
> >> Peter Grenader wrote:
> >> 
> >> Re: [sdiy] Buchla Lowpass Gate Switch I was
> >> unclear.  I was meaning if you overdrive a vac in
> >> general, not necessarily  in this circuit.  I've
> >> did it on my 291 clone.  I had to attenuate the
> >> input a bunch so it wasn't kazooing on me and
> then
> >> bring it back up to volume on the other end.
> >> 
> >> 
> >> mark verbos wrote:
> >> 
> >> 
> >> wait a second.... overdriven? Isn't it
> >> just a resistor? Something else int he
> >> signal path must be causing that, no?
> >> 
> >> Mark
> >> 
> >> 
> >> 
> >> Peter Grenader wrote:
> >> 
> >> harrybissell wrote:
> >> 
> >> 
> >> 
> >> If you are looking
> >> for "full on" by all
> >> means blast as many
> >> photons as
> >> possible... but
> >> 
> >> 
> >> Careful on this.  Vactrols
> >> make anything going through
> >> them sound like a
> >> kazoo when they are
> >> overdriven.
> >> 
> >> 
> >> 
> >> 
> > 
> 
>