[sdiy] Variable slope with a SSM2164

[HOSHUYAMA]

Hello Aaron and Sid,

 > 1) For a variable slope, based on my electronote recollections, ...

JH have built a variable-slope high-pass filter:

   http://jhaible.heim.at/jh5/jh5.html

Though the link to the schematic is missing, the frequency response
would help your student to design the multiples.

 > 2) There's a note that "clipping is needed for smooth sine wave
 > oscillation." No kidding! ...

Hahaha!  When I test something on breadboard, I always use a small
low-voltage-operated amp to save my ear ;->

 > Any other ideas re: the clipping? Maybe try something more like in the
 > original MS-20, with the three diodes?

Any type of clipping will work.  Some notes in the following site might 
help you to get interesting sound.

   http://www.muzique.com/lab/main.htm



Sam HOSHUYAMA
Saitama, JAPAN.

Aaron Lanterman wrote:
> 
> One of my students (Sid) is trying to built a variable-slope filter for 
> his project. I read up on some variable-slope ideas in electronotes, and 
> considered his project worthy enough to sacrifice one of my SSM2164s to 
> the cause so he could avoid having to build four separate converters.
> 
> He started with Osamu's design as a base:
> 
> http://userdisk.webry.biglobe.ne.jp/000/024/65/1/VcfSSM0602a.GIF
> 
> He got it working quite nicely. The input turns 1 V into 0.2 V, since 
> the circuit, as set up, seems to work on a 0.2 V/octave sort of thing at 
> the control pins of the 2164 (assuming we calculated things right in the 
> lab the other day).
> 
> Two questions:
> 
> 1) For a variable slope, based on my electronote recollections, I 
> suggested he drive the first stage as shown; but then for each 
> successive stage, add some multiple of a "slope" control voltage, like 
> this:
> 
> mainCV + multiple1 * slopeCV
> mainCV + multiple2 * slopeCV
> mainCV + multiple3 * slopeCV
> 
> This is simply implemented with a few summing nodes and op amp buffers.
> 
> Realizing that, at that stage, things are 0.2 V per octave. Thinking 
> that a 0-5 voltage would be a good slopeCV range... any thoughts on what 
> multiple1, multiple2, and multiple3 should be to get the poles spreading 
> out in an interesting way as the slopeCV goes up?
> 
> 2) There's a note that "clipping is needed for smooth sine wave 
> oscillation." No kidding! If he cranks the resonance past a certain 
> point, the scope goes insane. In the audio range, it makes everyone in 
> the lab rapidly pissed, and it will also seem to oscillate in the 
> above-audio range - you can't hear it, but you can see it on the scope.
> 
> So, I suggested he try Rene Schmitz's MS-20 clipping circuit, with the 
> LEDs. I haven't heard what it sounds like myself, but my student said he 
> didn't like the way it sounded. (He hasn't spent a lot of time with a 
> real MS-20 though, but here I was hoping to go for something more smooth 
> than an MS-20 anyway).
> 
> Any other ideas re: the clipping? Maybe try something more like in the 
> original MS-20, with the three diodes?
> 
> As before, I'm going to post all the student project reports, so 
> everyone can benefit from our efforts and the combined feedback.
> 
> - Aaron
> 
> ----------------------------------------------------------------------------- 
> 
> 
> Dr. Aaron Lanterman, Asst. Prof.
> and Demetrius T. Paris Junior Prof.    Voice:  404-385-2548
> College of Electrical and Comp. Eng.   Fax:    404-894-8363
> Georgia Institute of Technology        E-mail: lanterma at ece.gatech.edu
> Mail Code 0250                         Web:    
> users.ece.gatech.edu/~lanterma
> Atlanta, GA 30332                      Office: Centergy 5212
> 
> 
> 
>