Yamaha OD-100

[Mark Hammer]

Picked one of these up today for $5 at a music store "garage sale".  The price was right, and I figured even if it was busted beyond repair, the chassis and pots would justify the outlay.

As luck would have it, all it needed was 3 knobs, which I had.  Works absolutely fine.  Not an inspiring overdrive, overall.  Only really seems to have one character, but it's very smooth sounding, if tat's what you want.

Took it apart, and I have to say it is one of the most complex overdrives I've ever seen.  I can't tell if its overdesigned for what it does, or whether whatit does requires that much to do it.  A 571 compander, and three 4559 dual op-amps.  Bear in mind this thing has gain, tone, and volume controls, and that's it.

Anybody have any clues as to why it needs all that stuff?  I will say that it's quiet, which I assume is the role of the 571.

[Quackzed]

if its comp--- diodes to ground----expander it might be using the companding to get a softer knee out of the diode curve... make the signal relatively smaller and compressed with a log amp, then through diodes for a nice softer knee due to not slamming the diodes into hard clip region, then expanding back to big signal size for tonestack etc... hence the smoothness? just a guess, i see people selling the service manual and had no luck with a quick look for a schem...
it might be a good candidate for other instruments as a side thought... keys might sound good, or bass... due to the compander chip... though the frequency character may or may not be optimal.
ps. just found some yamaha nsa-636 speakers that i'm gonna use as recording monitors for cheap. gotta love used yamaha stuff. still under the radar , but they made some NICE 'junk' over the years!