[sdiy] Serge Triple Waveshaper mods

[Michael Ruberto]

Harry,

I don't have the circuit connected anymore so I cannot read what voltage is 
at the wiper of the pot. I believe I just adjusted it for gain. I fed the 
circuit a 1 volt pp saw and the output was 4 to 5v pp with a varying amount 
of offset dependent on the CV voltage.
I was using 0-15V "CV", it was just a trimmer between ground and V+. I did 
not change much of the circuit just some substitutions where I didn't have 
the right value.
For the trimmer I used 20K instead of 25K, should not have any effect on 
operation.
I did not have a 0.47uF cap for the input so I used a 1uF polypropylene. And 
because I only had a 1V pp saw to test it with I made the input resistor 
100K instead of 220K. I also did not add the AC coupled output in Stone's 
schemo. So besides my mods the circuit is more or less as drawn.

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 10:37:06 -0700 (PDT)
>
>Can you tell me the voltages that you send to the
>various inputs and the level of the sawtooth.
>I remembered that I have a spice simulation set up for
>this... I'd like to see if I can duplicate your
>results.
>
>Can you tell me how you adjusted the trimpot on the
>output (for gain, offset, cool sound whatever ???)
>
>1) The glitch you described IS the retrace of the
>sawtooh.
>
>2) The sinewave is probably because of the larger
>cap you used... I think its more LPF than waveshaper.
>
>Hey with a couplt of folks on this we might put the
>waveshaper to bed once and for all.
>
>I have some EFM versions of this, mebbe I will build
>one.
>
>H^) harry
>
>
>
>
>
>--- Michael Ruberto <frankentron at hotmail.com> wrote:
>
> > 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
> > > >
> > > >
> > > >
> > >
> >
> >
> >
>