[sdiy] Help needed with ASM based VCO

[René Schmitz]

Hi Chris and all,

> The original FET I was using was (no laughing!) a
> 2N3819. I realise now why it wasn't working.

If you had raised the 18p cap to something like 22 or 47p it would have 
worked also. Just giveing the FET a little more time for the discharge.

> Perhaps I should add that I am self taught, and
> learning all the time :)

Thats the case for me as well. And I'm still learning new tricks. :-)

> I would assume that the capacitor is being fully
> discharged now. As you mention René, I do have a few
> issues with the triangle waveshape - The bottom of the
> slope drops down sharply and then shoots back up - It
> is difficult to trim it into shape using the controls.
> Perhaps I should reduce the value of the discharge
> capacitor now (18pF).

Not sure what you mean by that. Is it that the slopes of the
triangle don't really connect?
In ascii it would look something like this?
\  /
  |/

That would be cured by changing the DC offset prior to your saw to tri 
converter. If the range of control for your trimmer isn't sufficient, 
you just need to make the resistor a little smaller.

> P.S. Nice to see you replying René - It was your
> website that partly inspired me to build the synth I
> am currently constructing. In fact, it was literally
> yesterday that I knocked up the Yash (LM398) Sample &
> Hold circuit as detailed on your site - It works well
> :)

Great to hear that!

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159