Serge Waveshaper schemos on Music Machines

[Jim Johnson]

Thanks for the clarifications, Sean. I had forgotten about the Triple
Waveshaper - it's been a while since I drooled on my Serge catalog.

But as in all scientific endeavours, the best answers only lead to more
questions!

- Is that really a unipolar supply? Is that standard for Serge stuff? In
that case, shouldn't the output be capacitively coupled?

- Does the diode next to the inputs of the op-amp connect to to both
inputs, or just the upper (-) pin? 

- What is the difference between the two CV inputs?

Jim Johnson 
Metaphoric Software
-------------------
Makers of Techno Toys
Software for Electronic Music
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*********** REPLY SEPARATOR ***********

On 7/16/98, at 4:44 PM, Sean Costello  wrote: 

>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