[sdiy] modular synth "standards"

[Don Tillman]

   From: "Tony Allgood" <oakley at techrepairs.freeserve.co.uk>
   Date: Fri, 23 Feb 2001 17:38:36 -0000

   DT>For a 10V p-p output, the audio sawtooth wave would then go from
   DT>-5V to +5V volts while the LFO modulation sawtooth would go from
   DT>0V to +10V. 

   I would tend to disagree. And I say tend, because both options have
   their place. And Harry did say there were two schools of thought here...

   I would hate to think that a triangle or sine LFO would vary between 0
   and +10V. 

Certainly.  I didn't mean to imply that all LFO signals should be
0V to +10V.  Triangle and sine would definitely be -5V to +5V.  For a
classic example, check out the ARP 2600 VCOs.

   But I also find that I would like a 1V p-p LFO signal for driving
   VCO pitch. I find that even with a log pot, I can't get the
   precision in vibrato when using the straight 10V p-p into a
   attenuated '1V/oct' input. Using an additional secondary 10:1
   divider gives me the control I need. Didn't the Roland 100M modules
   have a 10:1 switch on some of the CV inputs? Good idea that.

The ARP 2600 did something similiar; for the VCOs and the VCF, with
multiple control inputs, the first control input has the most
sensitivity, the next one less, and so on.

   The difference in standard audio and modular levels is not really that
   bad. 

True.  But this choice also determines the functionality and types of
modules you'll have.  (Ie., the ARP 2600 has no LFOs.)  (Again with
the ARP 2600!)

Further, if the audio paths are required to work at a full +/- 10
volts or so, you potentially have severe restrictions imposed on the
circuit design.  (This only applies to opamp haters like myself.)

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com