[sdiy] Serge Triple Waveshaper mods

[Michael Ruberto]

Yes it's actually running from only +15v

M. A. Ruberto


>From: xamboldt <xamboldt at earthlink.net>
>To: <synth-diy at dropmix.xs4all.nl>
>Subject: Re: [sdiy] Serge Triple Waveshaper mods
>Date: Fri, 02 Sep 2005 12:44:45 -0400
>
>On his version of this (the Wav1B), Tom G added a "Shape" pot - top of the
>pot to +V, bottom to ground, wiper through a 3M3 resistor to the
>non-inverting input of the 3900...
>
>My wav1B is currently on my "to fix" pile as it left me a little
>underwhelmed. I'll give your mods a try when I'm working on it. I think
>there's something else screwy with it, as the closest thing to a triangle 
>or
>sine I can get out of it is what sounds like (no o'scope!) a little +DC 
>bias
>with a tiny triangular dip in it. Oh, well.
>
>You said you're powering yours from +/-15V - did you mean +15V and ground?
>I've only ever seen this running from +V (pin 14) and ground (pin 7).
>
>-Chris
>
>On 9/2/05 11:58 AM, "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
> >
> >
>