[sdiy] MG-1 Mods (patching it out)

[WeAreAs1 at aol.com]

In a message dated 7/2/05 1:34:27 PM, philgallo at attglobal.net writes:

<< The loading effect noticed on the envelope  drive to the VCF maybe an
indication that you aren't using a series resistor (but feeding the envelope
directly) to the passive summing network at the input to the VCO expo.  A
series value of approx. 5.1K would maintain close to 1V/8ve response.

If you want to drive both VCO's you can input the envelope (with perhaps a %
of modulation attenuating pot) to the input of the control voltage summer
for the VCOs at U8.  A 10k resister in series between the envelope  (or the
output of it's attenuator pot) and pin 2 would do the trick. >>

Michael,

Phil is absolutely right about this.  You didn't ever mention if you had 
installed any sort of series summing resistor between your EG output and the CV 
input at your VCO expo amp.  I just assumed that you did add a summing resistor, 
because, well, that's what you're supposed to do.  Such a resistor is 
definitely needed.  If you don't have this resistor, it can result in some strange 
and unwanted interaction between your EG, your VCO, and even your VCF -- exactly 
the kind of interaction you have been observing.

If you don't already have the resistor, you should remove the new diode, 
install the summing resistor as per Phil's suggestion (either at pin 2 of U4 or at 
pin 2 of U8, depending on whether you want to modulate just one or both of 
the VCO's), and ignore all the other previous advice I gave!

Michael B.