electronics for a diy ribbon controller

[Puentstein]

In a message dated 98-02-27 16:58:43 EST, mgranger at greenville.infi.net writes:

<< This almost has to be from 60 hertz hum getting mixed in with your
 control voltage outputs. The output from controllers like ribbon
 controllers and keyboards is supposed to be DC, and any hum voltage will
 result in FM modulation of what they are controlling. Might want to
 shield the circuit and/or passively low pass filter the output to help
 eliminate the problem. >>
Thats a good idea and I'll use it once I get down to the tweaking stage.
But, (hangs head in shame!) my problem was due to operator error!
Figured it out by accident (how else!)

I was doing this:                    Vout                           ^g        
                                            -I--------------------------------
I-        tape                     
                                            ----------------------------------
-V+            bar                                       
 
but the synth wanted this:                                  Vout   ^g  
                                            ----------------------------------
I--I          
                                            ----------------------------------
---V+

(of course other configurations are possible)

Randy