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3340: Waveshaping
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author 3340: Waveshaping
ixtern
In ordinary applications CEM3340/AS3340 can provide only pulse, triangle and saw waveforms. There is a way to waveshape 3340 saw output to get different waveforms.
But don't excite too much - such waveshaping affects frequency and amplitude of 3340 outputs so this method is not very useful for using 3340 as 1V/Oct VCO. Maybe it may be used in LFO or effects oscillator mode. Only modulation by LFO where shape, amplitude and pitch are modulated but average frequency remains unchaged, perhaps may be applied.

Here is the test circuit diagram, base on the modded TH VCO Maximus (it doesn't matter as only basic 3340 features are used).
Soft sync input (pin 9) is used for waveshaping and simple test circuit allows to set (by pots) modding signal DC level and amplitude. Pulse and triangle from 3340 are taked for modyfying saw shape.,

Please notice that some combinations of level and amplitude of modding signal at pin 9 may result in lack of 3340 oscillations or oscillations at very high freqencies.

Here are some examples od waveshaping taken from "saw" output of VCO module (yellow line). Blue line is the modding signal taken at pin 9.

Modding signal: pulse.





Modding signal: triangle.





Last case is the modulation by triangle LFO. For me it's the most interesting as it is "all-in-one" - simultaneous amlitude, frequency and shape modulation.


BugBrand
I still haven't got a 3340 test circuit built up... but, would feeding one of the regular wave outs back into the linear FM input generate anything of interest? That's a technique for waveshaping on a sin-core-quadrature VCO - can take sine to something approaching saw - without the drastic freq-change of exponential modulation.
ixtern
BugBrand wrote:
I still haven't got a 3340 test circuit built up... but, would feeding one of the regular wave outs back into the linear FM input generate anything of interest? That's a technique for waveshaping on a sin-core-quadrature VCO - can take sine to something approaching saw - without the drastic freq-change of exponential modulation.

I didn't checked it but the output effect may be better or worse, as it affect current for the frequency capacitor but not the waveform switching levels. Applying signal with DC surely will change frequency, but without DC? I am not sure of end effect.
The Real MC
Be careful - if the triangle output is loaded down too much, it can affect tuning.
ixtern
The Real MC wrote:
Be careful - if the triangle output is loaded down too much, it can affect tuning.

So it means that pitch capacitor buffer is weak perhaps:
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