[sdiy] Serge Triple Waveshaper mods

[Harry Bissell Jr]

Fascinating, Captain...

Now I wonder why it says "no decoupling capacitor"
on the schematic. Is this because there ISN'T one
on the original, or because it will not work with
one.

I would be very surprised to see 'no decoupling
capacitor' on such a design, but there are times when
you don't WANT to use one.  Some 'bent' CMOS circuits
acting as linear devices should NOT have decoupling
caps... and in those cases the schematic should SAY
that.

Ken ???   Anyone ???

H^) harry

--- Michael Ruberto <frankentron at hotmail.com> wrote:

> Hi all,
> 
> I have been playing around with the fascinating
> triple waveshaper by Serge. 
> I am using Ken Stone's schematic:
>
http://www.cgs.synth.net/synth/serge/pic/schem_tri_wave.gif
> 
> It's an interesting circuit and truly does convert
> saw waves to sine. I did 
> find, however, that it does so with a big glitch,
> might this be because I am 
> powering it from +/- 15V?
> I eliminated the glitch completely by replacing the
> 100pF cap with a 2200pF.
> 
> While I found the circuit to operate properly I
> wasn't too excited by it's 
> sound. Rather boring for my tastes. So of course I
> had to experiment...
> I managed to get a much more interesting sound by
> removing the diode in 
> parrallel with the 2200pF cap (formerly the 100pF).
> Now the circuit will not 
> only transform the saw to a sine but will continue
> on to a trapezoid and 
> then square.
> This makes for a wider range of timbres over the CV
> sweep and really reduces 
> the yawn factor.
> 
> Also, reversing the polarity of the diode between
> the 2 inputs yields some 
> rather different looking waves.
> I guess since I'm building 3 of them I'll have a
> normal one and 2 
> differently modded ones.
> 
> The LM3900 is suprisingly still available and easy
> to find. I bought mine at 
> a local marine electronics store of all places but
> many places on the web 
> are carrying it. Allied has it for 77 cents and
> their part # is 735-5442.
> 
> If there are any more interesting mods for this
> circuit I would love to see 
> them.
> 
> M. A. Ruberto
> 
> 
>