JH's VCO, wavetable source

[mbartkow at ET.PUT.Poznan.PL]

Thanks, guys.

JH: 
Yes, I tried 470pF and 220nF. My core operates on ca 7.2V taken from
typical 723-based source. It seems that there indeed might be some internal
transistor capacitances that slow the switching. Maybe it is possible
to add some smart compensation capacitors ?
I realy love the simplicity of the circuit and would prefer to stay with it.

MC: 
Do you mean the triangle integrator-comparator circuit with symmetrical
charge and discharge ? There are two types of design I saw:
1) The polarity of the control voltage is smartly inverted using a FET, a 
CMOS gate or even a bipolar transistor operating in inverse mode (I have 
built this version several times and also observed scale flatness in the 
upper range)
2) OTA-based vco, like the one shown in tom's cookbook. It is more elegant
and simpler, but keeps me worying about the linearity, too.




Well, anyway what I need is a sound source with a wavetable containig 
256-times oversampled waveforms. This means that it either:

1) requires a VCO going linearly to megahertz (practically impossible,
right ?)
2) requires sample droping at higher clocking rates. Not easy, since
I would like the possibility to continously scale it several octaves 
down by pitch envelope, bend and for deep FM without hearable sampling
artifacts.

regards,

mb


--

Maciej Bartkowiak, PhD
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