[sdiy] Roland MKS-30 mod questions (xpost)

[juju selwyn]

I've been slowly putting together plans to modify my MKS-30. Given the
nature of its design, I'd like to do this without drilling holes and
such. Luckily the headphone jack as well as the volume and brilliance
sliders on the front panel are pretty much useless to me.

One of the first things I'm going to do is patch an audio input to a
cut trace between the noise source and selector IC. Cary Roberts
graciously pointed this possibility out to me on AH a while back. A
switching jack would disable the noise source and route audio in to
every voice. I'll be sacrificing one oscillator, as the noise is
considered a setting of osc 2 on the programmer, but that's alright. I
think I should be able to replace the headphone jack with a good
switching jack, and I'd be almost there.

Thing is, I know we're dealing with some pretty hot levels in there,
and I'd hate to have to devote a preamp to getting a good tone when
using this audio in. If it sounds good, I plan to use it a LOT,
especially if I get the EPROM upgrade later with chorus speed control.

Semi-lazy proposal: Disconnect headphone amplifier input from the
final (post-chorus) VCA output. Route new audio input to one channel
of the (stereo) headphone amp input. Send headphone amp out to the
original proposed noise-selector trace point. Replace volume slider
with appropriate value resistor (there is a level control on the PG200
and I hardly even use that) for the master volume, and use the slider
to control the headphone amp (now audio-input) gain. Of course, this
is hoping the volume slider is an appropriate value for the headphone
amp CV, but that seems like a relative minor concern at this point.

Of course I'm a noob, but it seems to me like this would be just
around the right amount of boost. Any comments? I have a multimeter
but no scope.

Also, does anyone have any idea how much overdrive the IR3R09 filter
can take? I assume not much, but I recall that some have added filter
overdrive to their SH-101s (same chip). Should it make a difference
that the MKS-30 uses the A1QH800170 surface module, same as the Juno
106?

Thanks,
J.