[sdiy] MG-1 first mods, VC res

[Metrophage]

> Did not work as I expected! The two outputs of the filter now go
> through the +/- inputs of a 3080 instead of TL071. Applying a
> modulation source to pin 5 barely changes the resonance.

After a few weeks of working on other stuff (707, DR110, Phatboy,
mods), I have gotten back to the MG-1. Quitting my lame 3rd shift job
has helped also.

As Phillip pointed out, I needed to remove R99, feedback resistor to
the resonance amp, for real "emphasis" control. With just the LFO
signal, the modulation amount is not sufficient... but with a 100k pot
between the supplies it sounded quite good! I suppose I'll add a CV
scaler to the mods for the LFO and other signals. Next is to cut the
traces around the res slider and wire them as I had done the pot I used
to test.

I have started the board of extras. First circuit is an envelope
follower with trigger and gate extractors - the one from Barry Klein's
book. I knew that besides an external input to the filter, I'd want
another source of envelopes! I might need to make switchable caps for
fast/ slow signals. More testing of this circuit hopefully later today.

Other things going on this board are an input summer for the VCF, maybe
CV summers for the filter cutoff and res. The filter caps are moving to
this board, so they can be switched out for lower-frequency ones. I'm
going to try to make Wolf's retrigger circuit on here also. Lastly,
before the Feature Creep arrives, PWM controls and a new LFO/VCO. No
reason not to vary the modulation rate with the MIDI>CV converter!
Also, the envelope sliders are 1M; I am going to try to make external
CV controls for these, probably with Vactrols, to keep things simple.

The back panel is going to get drilled out like Swiss cheese, and I
might need to put full 1A regulators in place of the stock 500mA
devices. Oh, yeah - I replaced the power supply filter caps, and
mounted the original regulators on larger heatsinks with fresh
goop.These things get extremely hot! Might this be because the 58vct
transformer is a but much for +12/-15 volts? I wonder if the regulators
might be happier with something like 35vct. Opinions?

CJ

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