[sdiy] Ripple on a Metasonix R60 MIDI 2 CV

[David Ingebretsen]

I wanted to build a MIDI 2 CV into my Synthasystem and bought a Metasonix
R60 self tuning module. I put it behind a custom panel to match, and
therefore voided my warranty. I know, I know, but I'm used to this SDIY
thing.

It completes its tuning cycle, but then there is some serious ripple on the
CV output. As the CV increases, there is an increasing magnitude ripple at
about 200 to 400 Hz. At a 4 volt CV, the ripple is about 200 to 300 mV and
distorts the sound terribly. There is a scope grab on the Electro-Music
forum:

http://www.electro-music.com/forum/viewtopic.php?t=51817

I've tried with 3 different VCOs: JH Living VCO, MOTO Ultra 300 VCO, and the
Steiner VCO. I've tried 4 different MIDI controllers.

I wrote Metasonix, told them I mounted it behind a different panel
understanding that likely voided the warranty and offered to pay in advance
to have them take a look at the problem, but was basically told to trouble
shoot it myself; except a little more bluntly...

I don't have the schematic or source code for the processor, so any ideas
where to start? It looks like a pretty simple PCB, however, I suspect it is
something other than a bad OpAmp.

Otherwise, I've got a $350.00 paper weight...

David