[sdiy] Revisited: Buchla 292 finished!

[Grant Richter]

It true, Peter G and I just love those Lowpass Gates.

Here's the deal with the switch:

VCA mode switches the 18K resistor across the 910 pF and it becomes a
resistive attenuator

The middle "combo" mode disconnects the resistor and forms a very soft 6-12
db/oct variable lowpass. As Buchla puts it "simulates the psychoacoustic
effects of approaching and receding sound sources" for location modulation.

In the Lowpass mode, gain of 1 feedback is switched into the 0.0047 cap
attached to the center tap making it into a Sallen-Key. This feedback raises
the over all gain by 3 dB, so a 3 dB pad is also switched into the input
stage to keep the output gain constant.

> From: Peter Grenader <petergrenader at mksound.com>
> Date: Sun, 13 Oct 2002 21:01:36 -0600
> To: <keithw at cix.compulink.co.uk>, <synth-diy at dropmix.xs4all.nl>
> Subject: [sdiy] Revisited:  Buchla 292 finished!
> 
> Everyone (especially Keith Wintanely),
> 
> I just awoke in a sweat realizing the switch symbol  on my redrawn Buchla
> 292c LowPassGate schematic may not clearly indicate one important feature,
> although I do mention this in the introduction:
> 
> The toggle switch is an ON-OFF-ON type.  This is VERY important.  If you use
> pme without that center position, you'll loose  the famous 'combo' mode that
> made this unit what it was.  This allows the a mixture of the lowpass filter
> and straight amplitude mod function and all that fantastic ringing.
> 
> Keith, if you used the wrong one, fear not - just replace it with an
> ON-OFF-ON type and you will be set.
> 
> OK, back to bed now.
> 
> Night.
> 
> P
> 
> 
> 
> 
> Keith Winstanley wrote:
> 
>> Hi all
>> Just finished Buchla quad lowpass gate module - works first time
>> and sounding good more soon I am too tired to write more now.
>> Many thanks Peter for your timely hints and tips, saved me pulling
>> things apart again.
>> 
>> cheers...
>> 
>> Keith
>> 
>> http://home.freeuk.net/lowpass
>> 
> 
> 
>