Archive of the former Yahoo!Groups mailing list: MOTM

Ah ha! My 300 did not die! It just got hot. And when it got hot it
stopped working. But how it got hot is a bit of a mystery to me.

I had tuned up my 300, and was enjoying the lovely round sound it
produces. I plugged it into my wee 420 and began to enjoy the filter
as well. I had sawtooth out going to the filter in, and filter out to
a tiny amp I have on the bench. At one point I decided to turn the
res control to "10" on the filter, it went into self osc, I turned the
freq all the way up too (on the filter) and it went beyond what I
could hear or the poor little amp could put out.

After that the 300 started acting very strange, its pitch became
unstable, and within 45 seconds it would not produce waveforms at all.
At this point I got bummed, and went looking for trouble on the 300's
circuit board. After 20 minutes of looking, and finding no wave form,
nor anything that looked wrong besides the lack of output from Q2, I
shut the whole thing down.

Hours later I came back (could not sleep, was trying to figure out why
it was busted), powered it up and it worked. My workbench is in the
garage, and it is currently about 55 F in there most of the time. It
came up, had the saw out straight into the amp, and it held steady for
about an hour with no problem.

I did find that if I blew on the board, it would shut off, just to
come back on in about 20 seconds. I knew the circuit was temperature
sensitive, but should I consider building some little enclosure for
the Q1/Q2 pair? Anyone have any idea how an MOTM-420 would cause that
part of the circuit to get really hot and shut down? Both modules
seem to work sonically pretty well, but I am concerned that something
is wrong…

Bruce