[sdiy] Serge Triple Waveshaper mods

[Ken Stone]

That is merely an representation of what was actually there on my original
Serge board. Personally, I'd add them.

Ken

>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
>> 
>> 
>> 
>
>
_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au or sasami at cgs.synth.net
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
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