[sdiy] Serge Triple Waveshaper mods

[Harry Bissell Jr]

Hi Michael (et al)

Some more simulation confirms the larger cap is
causing a substantial amount of filtering. I found
some settings that do give a nice 'sine wave' with a
sawtooth input.  I'm using CVs of positive and
negative 15V max.

H^) harry

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

> 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
> > > > >
> > > > >
> > > > >
> > > >
> > >
> > >
> > >
> >
> 
> 
>