Serge Waveshaper schemos on Music Machines

[Sean Costello]

Jim Johnson wrote:
> 
> Coupla questions for anyone who has seen the Serge schematic Sean Costello
> located at Music Machines, for anyone who cares to hazard some guesses.
> 
> 1) Which waveshaper is it? It looks closest to #2 based on the number of
> ins and outs, but it's not a perfect match.

It is actually the variable sawtooth-to-sine waveshaper from the Triple
Waveshaper module, and the old oscillator designs.  Unfortunately, this
isn't the Wave Multiplier circuit - but I feel that someone smart can
combine this schematic with the Serge Tcherepnin patent to figure out at
least part of the Wavemultipler circuit.  The VC full-wave rectifier
should be a simple adaptation of this circuit.  I breadboarded a single
VC rectifier stage a while back, and it sounded really nice while
sweeping the control voltage.
 
> 2) Anyone know which input is which?

The middle input is for the (sawtooth) input, the other two inputs are
for the control voltages.

> 3) What's the polarity of the op-mp - which terminal is +?

Doh!  I forgot to put that in when I relabeled the circuit.  I'll look
it up on my original diagram when I can find it.  My guess is that the
top terminal is (-) and the bottom terminal is (+), since the (+)
terminal is where the control voltage is applied in other LM3900
applications (the VCA design in Electronotes #41, for example, which is
a modification of the VCA in the National Semiconductor application note
AN-72).

> 4) Why use an LM3900 in this circuit, rather than a TL-074?

As Dan Higdon just wrote, the LM3900 is the heart of the circuit.  Go to
http://www.patents.ibm.com, select "Search" and do a search for
Inventor:Serge AND Inventor:Tcherepnin.  One of his 2 patents covers the
really super keen techniques Serge came up with for the LM3900.  Paia
also used the LM3900 extensively in circuitry.

Later,

Sean Costello