Hello fellow MOTM'ers,
After constructing my 300 VCO, I ran into a wierd problem wich I'll
try to describe here.
I can actually "hear the VCO cap (C15?) charging", at least this is
what I think is happening. This can be heard best when listening to
the pulse out, I can hear the "tick" of the waveform but also a very
annoying beep wich seems to reset at every tick. (Coarse and fine pots
turned all the way down)
I think I'm only supposed to hear the tick, right? :) Also the '900
PSU is actually singing along with the beep noise, wich I find quite
scary to be honest. This sounds like a very high frequency
noise/whine. All the VCO outs, present the same whine together with
the actual waveform.
I checked the placing of all the parts, solder joints, especially the
dual JFET. It all looks fine as far as I can tell. All the
measurements in the troubleshooting section check out fine, except for
b and f.
VX measured (as noted) to the right side of R3, gives me -15.18V
(again, pots turned down). When I measure VX between R29 and R36, I
get +4.76V.
Pin 1 of U4 goes from -0.2V to -0.5V approx., when I rotate the coarse
pot. Everything is measured in respect to ground, wich I assume is how
it's supposed to be done.
Any ideas? I'll be happy to provide any more clues, if needed. I hope
I did all my "homework", and this isn't something awefully stupid.
Kind regards,
--
+-------- - -- -
| Sjaak Jobses <
sjaak@...> ++
http://rxj.nl+---- - --- -- -- -