A couple of days ago, I just finished building my 4th and 5th MOTM-300 VCOs.
Even though this is a "more difficult" kit in terms of the number of parts
and such, it is probably the most fun to build. What a great kit and VCO
Paul !!!! :)
Now having said all that, There are two things about the great MOTM-300 that
I wished were a little different.
First was "at least" octave switches. That problem was solved and made
better for many of us with the DIY 822 and 831 voltage switcher projects.
Now we have instant interval and octave switching and even transpose on the
fly.
Second was the fine tune control range. The fine tuning has never been
"fine" enough for my personal taste. I have always felt the range of the
fine tune control was greater than what I liked. The fine tune control
seems too touchy when trying to zero beat oscillators to me. So, I have
modified one of my VCOs (and will soon do the other four) so that the fine
tune control is more fine.
On my stock MOTM 300s, the range of the fine tune control is about 11
semitones. I wanted something in the 2 to 3 semitone range on that control.
The modification is simple and virtually non-destructive. It requires adding
one 270K resistor to the circuit board and cutting one trace. Since the
trace resides between two via holes, the modification is easily reversible
by removing the resistor and inserting a wire jumper.
Details of the modification including a photo can be found at my web site:
http://www.modglin.com/larry/300mod.docLarry Hendry
P.S. Disclaimer: I am not an electrical engineer. Do not consider this
professional advice. However, this is a nice modification that works well.