[sdiy] Serge Triple Waveshaper mods

[Michael Ruberto]

I used a 1uF decoupling cap. Maybe it caused the sine glitch???

M. A. Ruberto


>From: Harry Bissell Jr <harrybissell at prodigy.net>
>To: Michael Ruberto <frankentron at hotmail.com>, synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] Serge Triple Waveshaper mods
>Date: Fri, 2 Sep 2005 09:20:36 -0700 (PDT)
>
>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
> >
> >
> >
>