Voltage Control

[Pehr]

I'm thinking of building my own analog effects (reverb, delay, chorus, phaser...etc), but I want to be able to control some parameters with a LFO or ADSR.
For example modulate the freq. of a phaser with a LFO.
Is it easy to mod an effect so that it can be controlled with CV?

[jksuperstar]

That depends on the circuit your modulating.

If you're lucky, and this is actually very typical in voltage controlled circuits, is there are points that having summing op-amps. If you have the schematic, you'll se it as several signals all going through similar resistor values into 1 single point, which is also the input into an op-amp. For your new control signal, just use the same resistor and add it to the sum.

The only thing you'd have to keep an eye on is your voltage levels. Keep you LFO at the same level the circuit is using.

If you're unlucky, you have to do some real surgery, and replace components to add you own circuit. This can become difficult for some filters (and similar circuits), that depend on a control knob being the actual resistor that modifies the cutoff for example, rather than part of a circuit to generate a control voltage which then controls the cutoff.

[bugbrand]

Hopefully tomorrow I will be able to update my site and show the world my new drone machine - much of this has been spurred on by all the Vactrol talks (phasing things).

Basically, I've made a simple Vactrol control board -- a range knob and two CV inputs that drives an LED / LDR arrangement - so each board gives a simple variable resistance output - tie this to anything!

What I've used this for is:: 8 vactrol control circuits which control four lofi (40106 simple) oscillators - each one has pitch and shape controllable by Vactrol and the oscs also do lo-freq or audio range..

The device looks frreaking beautiful (just got a load of beautiful knobs and it has about 24!) but I've got to tweak the insides a bit - it can make great sounds, drones, crashing bass, high twiddles, but its all a bit too chaotic right now.. Anyways, details of that tomorrow probably...

So, sorry, I'll stop hijacking! --- YES VACTROL control! 'tis the way for simplicity. Make your own vactrols!

[Pehr]

thanks for the help, I'll think of something ^_^

[bugbrand]

On page 2 of this Scott Bernardi VCDelay Schematic there's a simple vactrol drive circuit - CV input turned to variable resistance. ((note, the CV modulation input is inverted - I used this circuit and added a inverting summing mixer for the CV inputs.))

Other ways, as mentioned in the recent VCLFO thread ---> JFETs or LM13700

I quite like the way of vactrol control though...

[Pehr]

[bugbrand]

Well, there's just a lot of talk about vactrols around here at the moment..!..