Archive of the former Yahoo!Groups mailing list: MOTM

----- Original Message -----
From: edibennardo <endiendi@...>
I was happy enough with my VCA till I wanted to have both an EG and an LFO
controlling it... Any thoughts? Any suggestions about a possible mod adding
a second CV maybe with an attenuator too?
Enrico Italy

Larry Hendry writes:
OK, I'll take a shot at this. If I understand the circuit correctly, the
voltage applied at PIN 12 of the 3330 controls the overall gain of the VCA.
Paul has already built a summing node on the front end that sums the voltage
from the GAIN pot to the voltage from the CV MOD pot. I see no reason why
you could not add a 3rd input to that summing node. The only problem is
that you could end up with a resulting voltage that drives the VCA into
clipping if you turn both controls to max.

As I see it, the modification requires only 3 parts. 1 - add the input jack
2 - add a CV2 mod pot, connect the pot and jack just like J1 and VR1. 3 -
add a resistor from the wiper of new pot to the common point at R1 and R5.
Since a LFO is typically 10 volts swing, I think this resistor should be
100K or somewhat larger. 100K would cause this CV input to have about 50%
of the effect as CV input 1 (as I see it).

It seems to me if you use the LFO input, then depending on whether you have
a "+/-" or "0 to -" voltage you might have to adjust your "gain" pot off of
the "0" set point some.

Paul, Care to comment right or wrong?

Stooge Larry

Disclaimer: I am not an engineer. I am not telling you to modify your
MOTM-110. I am offering this modification suggestion for the purpose of
discussion and learning.