[sdiy] Memorymoog clone questions

Luís Marka luis.marka at gmail.com
Wed May 6 22:39:50 CEST 2020

Hi gang,

I am working in a Memorymoog clone - not an exact copy, the board 
layouts and the cabling are different from an original Memorymoog, and 
SMD components were used extensively. Other than that, I tried to keep 
all circuits as close to the original as possible.

Got to the point where I assembled all boards except for the right side 
panel board, and built only one voice card so far. Results look good so 
far: got "1 tuned" after autotune routine, so think I am doing it right.

A couple mysteries remain:

- In the DMUX board, there was no way to get my clone to read the panel 
potentiometers. Turns out the output of U6A, after resistors R13 and 
R14, was arriving at buffer U26 in the digital board as +5V for HIGH, 
and some 3.5V for LOW so I guess it was seen as just HIGH at the data 
bus. Replacing R14 with a 5K1 resistor instead of 15K did the trick, but 
I wonder if the schematics are wrong. Unfortunately I do not have an 
original Memorymoog to compare the actual circuit against the schematics 
(big mistake trying to make a clone of this complexity without a working 
unit at hand), so I am assuming there is an error in the schematics in 
this section.

- More or less the same issue in the S&H circuit at the Common Analog 
board. With resistor values for R219 and R220 at 8K2 and 10K, the S&H 
was not triggering with the LFO square wave output. I had to reduce R220 
to some 3K3, otherwise the S&H output was just the same filtered noise 
present at its input. Not sure if that could be because I used a 
slightly different FET, I replaced the E112 in the original with a J111. 
Or, could it be another error in the schematics?



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