[diy] moog VCOs

[Tony Allgood]

Hi all,

My thanks go to Juergen for illuminating my expo question.

Next thanks go to Tom and Terry for answering the E112 and J112 problem.
The J112 does have a different pin out to most other FETs I have.

Now my latest findings. The FET rds(on) doesn't seem to be the cause of
the problem I was having. That is getting the timing capacitor to sharge
fully to the +5V reference voltage. Looking at the scope, we have the
capacitor charging to its peak value a good 2.5uS after the gate pulse
has been removed. The gate pulse is a sharpish 0.5uS 10V pulse, and the
saw output only starts to rise half way through this, it completes the
full charge cycle at about 3 to 4uS after the initial edge of the pulse.
Perhaps the 2N3819 was too fast, and thus did not turn on long enough to
charge the cap. Of course, altering the comparator hysteresis would give
us more control of this, but this is not the point of my investigation,
which was to build a temperature stable version of the mini's VCO for my
new modular.

I will almost certainly do PCB for the VCO, since I will be wanting at
least four of these things for myself. The PCB size will be the same as
my Superladders, with board mounted pots for tuning and PW. Price will
be about 15UKP for one offs.

Regards,

Tony Allgood  Penrith, Cumbria, UK

Walsh synthesiser, SuperLadder, TB303 clone and rack mounted filter

http://www.techrepairs.freeserve.co.uk/projects.htm