[sdiy] Buchla Lowpass Gate Switch

[Scott Stites]

Hi Peng,

The SPDT center off switch should work.  That's On/Off/On, where the center position does not put the 7.5V on either 'throw'.  If you note the original Buchla schematic, that is exactly what Don Buchla used for a switch (the 'dot' in the middle of the switch symbol is the center 'off' position).  The 'Both' mode is actually in effect when both the Low Pass and Gate mode switch logic signals are 0V (all 4016 switches are open).  So, it's just how you have it now, just put that SPDT center off switch in, and away you go.

Peter Grenader devised a method to avoid using the 4016's at all by installing a (IIRC) 3PDT center off switch, which makes things a bit easier.  However, I am using Mark's adaptation of the Low Pass Gate using the 4016 mainly because 4016's are a helluva lot cheaper than those 3PDT switches (but that's just me).

Cheers,
Scott


----- Original Message ----- 
  From: Peng 
  To: synth-diy at dropmix.xs4all.nl 
  Sent: Tuesday, August 10, 2004 8:57 PM
  Subject: [sdiy] Buchla Lowpass Gate Switch


  Hi,

   I recently finished the Lopass Gate using Mark Verbos pcb. Works good. I put in a 2 position toggle to switch between lowpass/gate. I'd like to have a "both" position but can't figure out how to do it ( experiencing a brain freeze or something!). I have some SPDT center off and DPDT center off. 
    I had an idea to replace the -7.5V that goes to 1M resistor on pcb with +7.5V, then put  
  -7.5V to middle lug of toggle. That way, if it's in the center (off) position, I'd get the both response ? Just a guess. 
    I searched this out in the archives first (of course) but didn't find anything, though there are references made. As a side note: On the search page of SDIY I typed in " Buchla Gate" - no results. Next tried "Buchla" - many results. One read "Buchla 292 Lowpass Gate" - this should have come up on first search. Next "Buchla Lowpass" - nothing. Lastly "Buchla 292" - got results. Seems you need to get the words in order, or just try to get the first word. Maybe I'm missing something ? If not, then it's a good thing to keep in mind when searching ( or posting for that matter ).

  Thanks,
  P.


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