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examples of Blacet VCO being FMed???
MUFF WIGGLER Forum Index -> Fractional Rack Modules  
Author examples of Blacet VCO being FMed???
KoryB
Happy Sunday!

I really love the tone and 'color' of the Blacet VCOs, but I've yet to hear what they sound like being FMed...

Does anyone have an example they'd mind sharing?

Thanks!
fracmonkey
I don't expect that the fm would sound any different than most. The circuitry here is pretty typical of most vco.

It would also take quite a few samples to cover all the low freq, high freq, lin, expo, ac/dc choices.

Blacet currently has these on sale so maybe its a good time to pick one up.
addendum
OP: if you're looking to do dynamic FM, that is, modulating the index with CVs while the notes sound, then the most crucial element is the VCA that you use to attenuate the modulating VCO with that CV. It should have minimal DC offset to avoid (additional) pitch drift during CV level changes, harmonic distortion should be either minimal or at least to your liking, and the response curve should complement (not parallel) the slope shapes of your envelopes to allow for snappy transients.

About the Blacet VCAs I've only heard good things so far.
slow_riot
addendum wrote:
OP: if you're looking to do dynamic FM, that is, modulating the index with CVs while the notes sound, then the most crucial element is the VCA that you use to attenuate the modulating VCO with that CV. It should have minimal DC offset to avoid (additional) pitch drift during CV level changes, harmonic distortion should be either minimal or at least to your liking, and the response curve should complement (not parallel) the slope shapes of your envelopes to allow for snappy transients.

About the Blacet VCAs I've only heard good things so far.


The modulation and carrier VCOs are more important. For example, if there is DC bias in the modulation source the VCA will amplitude modulate it and it will no longer become DC and thus not blocked by the AC coupling capacitor on the linear FM input that we typically see. AC coupling on the input to the VCA may help with this, but the DC bias often is a result of asymmetry in the VCO core and again, this cannot be fixed with AC coupling because it is AC itself.

Older VCO techniques often meant asymmetry by as much as 1 volt (e.g. Zener diode clamping or reset points set with resistor dividers on the power supply rails). Modern techniques can give waveform accuracy that be as close as +/-10mV to the desired waveform and this changes everything. In my VCO there is no AC coupling on the linear FM inputs to the carrier oscillator. (I cannot make any claims about reaching high indices of frequency modulation as the master oscillator is simply too complex to manage DC offset without resorting to brute force methods, and an index of 1 (i.e. amplitude of FM equaling the amplitude of the carrier) is the maximum possible. High accuracy (and more importantly, simple) carrier VCO cores could go higher with clever design.
addendum
You are of course right that the "source material" is the most important. I was assuming that the Blacet VCO outs are as symmetrical as a "classic" and also normally priced (read: not Cirrocco prices or so) VCO design can be. I don't know if it is and how much of that depends on the builder or on parts selection, but if it is in the upper quality range of said VCO class, those VCA properties are the next most important factors. Don't know how useful it is to compare the Blacet VCO to yours or other very modern designs.
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