AW: VC pots

[Haible_Juergen#Tel2743]

> I would dearly love to see a comparison between or discussion about
>different types of VCAs - JFETs, OTAs, dedicated VCA circuits, motorized
>Potentiometers, DAC R2R ladders, etc. comparing cost/complexity to
>performance.

JFETs:

pro's: nonlinear (quadratic?) CV response is often desirable
            (in compressors and in phasers)
            small component, easy to layout the pcb
con's: very small voltages needed to prevent distortion
             => unually rather noisy circuits (at least together with
             cheap opamps as active elements)

OTAs:

pro's: cheap, easy to use, kind of "standard" in synths
con's: SNR limited to about 65 ... 75 dB


LDR + LED:

pro's:  very good SNR
con's: very slow


NTC + heater:

(just for the record. Don't know much about that, only
that this combination is quite common in ALC circuits
of commercial telecomunication systems)


motorized pots:

pro's: very good SNR
con's: very slow, very large, very expensive


special VCA IC's:

pro's: good SNR
con's: expensive and sometimes hard to get


DAC's, programmable pot ICs etc:

pro's: good computer interface
con's: staircase stepping


The list is not complete, I know. Maybe it's a start for
comments / additions, however.
And don't forget, sometimes the "con's" are a feature:
I *love* the distortion of my overdriven FET-based
cheap Phaser pedal!

JH.