Serge Waveshaper was Re: Harmonics question

Sean Costello costello at costello.seanet.com
Wed May 20 19:49:52 CEST 1998


At 09:59 PM 5/19/98 EDT, you wrote:
>
>In a message dated 5/19/98 3:52:56 PM, magnus at analogue.org wrote:
>
>>I recall seeing diagrams of such unlinear waveshapers. I even think
>>that we have discussed this several times. For instance do I recall
>>that the Serge waveshapers would do odd and even harmonics and that
>>the schematic is very simple indeed.
>
>
>Hi Magnus
>
>I wonder if you're confusing the Serge Triple Waveshaper with the Wave
>Multiplier module. One waveshaper is a very simple circuit based around one
>quarter of an LM 3900 and does non-linear "Harmonic Reduction" (unlike
>anything done in music theory). It is similar to a CA 3080 tri-to-sine
>converter I believe.

The Triple Waveshaper does two things:  it converts a sawtooth wave to a
triangle wave (via full wave rectification), and converts that into a sine
via, um, breakpoint...diode...thingies...(man, I wish I knew the lingo).
The amount of rectification is voltage controlled, as described in Serge
Tcherepnin's patent.

>The Wave Multipliers do some nutty half and full wave rectification (I
>believe) and have a whole lot of chips. The sound to me is very much what I
>would expect from the timbre modulator circuits in the oft mentioned
>Electronotes and in Barry Klein's book. I would never attempt to build one,
>too complicated for a timid sole such as me. Now if some one offered some kits
>of these circuits...

As far as I can guess, the Wave Multiplier works as follows.  (This subject
has come up a lot, but the Wave Multiplier is one of my big obsessions,
along with Moog filter distortion, the Barberpole phaser, and washing the
germs off of my hands several hundred times a day so they stop sending my
brain radio waves).

The first section is a simple clipping amplifier, that "rounds" the signal.
Possibly a CA3080 that is overdriven.  The amount of overdrive is voltage
controllable.

The second section is...well, no one really seems to know (prove me wrong,
folks!). It seems to work as follows: When the signal voltage reaches
certain thresholds (positive or negative), the signal "wraps around."  Easy
to do in digital (the Nord Modular implements it, and it sounds GREAT), but
I don't know how to do it in analog. 

The third section is four voltage-controlled full-wave rectifiers in series
(see the Serge patent for details).  Probably uses all four sections of a
LM3900.

Any more details, folks?

Sean Costello






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