[sdiy] Calling all Buchla lowpass gate fans

[David Ingebretsen]

It's a combination of VCA and/or low pass filter, I believe.

David

David M. Ingebretsen M.S., M.E.
Collision Forensics & Engineering, Inc.
2469 East Fort Union Blvd. STE 114
Salt Lake City, UT 84121
www.CFandE.com

801 733-5458 Office
801 842-5451 Cell

dingebre at CFandE.com
dingebre at 3dphysics.net



-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Aaron Lanterman
Sent: Sunday, June 14, 2009 3:32 AM
To: sdiy DIY
Subject: [sdiy] Calling all Buchla lowpass gate fans

OK, I can switch between three modes now - replacing the 51 ohm  
resistor with a 1 megaohm resistor, which is what it was supposed to  
be, helped quite a bit. ;)

Check this out:

http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_2080_10_20
0.jpg

OK, there's three CMOS switches there. One I'll call "top," which  
switches a 0.0047 sallen-key feedback cap in and out, and two I'll  
call "bottom," which are driven with the same control, that switches  
in and out a 15K to ground near the FET buffer and a 10K to ground in  
the feedback loop of the input buffer.

Testing the voltages at the control inputs on my CMOS switch, I see my  
three modes either:

1) Have all switches OFF.
2) Have the top switch ON an the bottom two OFF.
3) Have the top switch OFF and the bottom two ON.

All three modes have a different sound, but I'm not entirely sure what  
I should be listening for.

Question - is this what a Buchla LPG is supposed to do?

There doesn't seem to be a mode to have them all switched ON.

- Aaron
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