VC mixer from OTA's

[Don Tillman]

   Date: Sun, 30 Mar 1997 23:50:32 -0800
   From: Steven Varner <svarner at sdcoe.k12.ca.us>

   I've had a couple suggestions about using OTA's for each channel of the 
   mixer (similar to the EN-76/PCC option 3 VCA).  These would go into a 
   summing node.  One email suggested using a final OTA as a buffer
   amp. 

Hmmm, I wonder why one would use an OTA for a bufffer amp; they don't
score well in drive current or low output impedance.

(My choice would be a simple discrete source- or emmitter-follower
circuit.) 

									 I 
   started thinking that maybe I could use 2 OTA's in parallel with all 
   channels going in to both.  Then I could somehow have both a PAN input 
   and a manual pan pot going between the bias input of those last two 
   OTA's.  One OTA would lead to a right channel and one to a left.  The CV 
   pan or the manual pan would shift the output from right to left channel 
   for stereo effects.  

Sure, that would work fine.

However, my preference would be to place a panner circuit on each
input.  Y'know, like a regular recording/PA mixer.  Two OTAs and a
panning control voltage inverter per input, stereo summing busses.

The incremental cost isn't all that much, you save the second OTA
stage in the signal chain, and you can have *lots* of things flying
around between the speakers instead of just one.

  -- Don