[sdiy] Buchla Lowpass Gate Switch

[Peter Grenader]

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.
>> 
>> 
>> 
>> 
>