[sdiy] best floating voltage-controlled resistor implementation?

[Dino Leone]

I just read the discussion on the quadrature oscillator and realized that
this is actually of great interest to me.

I'm thinking of replacing the 100K pots (shape pots) in the timbre modulator
(EN#72) we discussed some two weeks ago with voltage-controlled resistors.
These are floating resistors in front of the zeners that chop the signal.

I believe there's 3 options and I'm wondering what would be the most
efficient/practical way?

1. Use the 13700 OTA as described in the datasheet? Disadvantage: quite big
circuit "just" for a VCR.

2. Vactrol. Can anybody tell me how fast they are? I've got some LDRs lying
around somewhere so I could breadboard this to check?

3. (I might get garroted here for mentioning this): digital voltage
controlled resistor. Disadvantage: limited to +/- 7V. and some digital
circuitry (which could of course be abused to implement some other fancy
stuff).

Any ideas? The vactrol approach seems to be the easiest and most economical.
But would it be fast enough?

Best Wishes,

Dino