[sdiy] Serge Triple Waveshaper mods

[Michael Ruberto]

Harry,

Aren't the input diodes blocking the affect of negative CV?
Interesting about the filtering, it didn't sound very filtery to me. Have 
you gotten it to produce the trapezoid with the top diode removed?

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 12:50:20 -0700 (PDT)
>
>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
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > > >
> > > >
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> > >
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> >
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