[sdiy] MG-1 first mods, weirdness

[Metrophage]

I have had the MG-1 running in better-than-new condition on my bench
for about a week, quite fun to play! The Juno106 at my parents house my
offer patch memory, but the MG-1 feels and sounds so much better!

Since I didn't have much time last weekend, I did only a few basic mods
to the unit so far. I added a new .47uF cap which can be switched in
parallel with the current LFO cap. The new higher LFO range has been
most fun with the filter modulation, set to just under oscillation,
where it starts to whistle. Playing inverse envelopes while varying the
"contour filter" and LFO rate nibbles at my ears.

Second very simple mod I have done is to replace the .022 S&H cap with
a poly foil type cap. Huge difference in the S&H, which can now hold
its signal for an entire note / musical event!

What's on the bench now is my filter input board. This has a real
filter audio input summing amp, and an envelope follower. The delay in
this project is that I cannot yet decide what sort of gate/ trigger
extraction to use (and I can't find my Zener diodes). The envelope
follower is basically the one from Barry's book. I am also moving the
.027 filter caps onto this board so  can switch between these or 1 uF
caps for (hopefully) bassier cutoff.

Stuff with test clips which has been fun is routing the LFO and
envelope signals to various parts of the synth. VCO freqs, pulse width,
top-octave (!), etc. I think I am going to bring many of these points
to the back panel, now that I've got drill bits which are big enough
for my 1/4" jacks. I am going to try VC resonance tonight as well.

Also going to see about another LFO/ VCO for expanded modulation
possibilities, including control from external CV. The detune slider
has a huge range when the sync switch is flipped, sounds especially
wild with the ringmod as main audio source! Going to try modulating the
detune voltage tonight.
Weirdness? Since I have begun testing the unit with my Frankenstein
headphones, rather than my computer speakers, I notice that the sound
is excellent - but there is always a high-pitched sound coming through.
The sound is in pitch with my key activity, complete with "glide"
setting! Maybe the master pitch signal? It is there even with all
"mixer" sources off, and even with the volume pot all the way down! The
synth would sound a whole lot better without the whine, but I really
don't know how to get rid of it. I guess I will try putting the 1k (or
better value) output resistor back on and listen to any difference.

I can't wait to get this unit finished and back in its case!

CJ



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