How would I go about doing this...

[Sonno]

Quick question for you all who know something about this kinda stuff.
How would I go about doing this?

I want to auto-modulate an effect parameter.

I'll give an example.
Say you have a basic flanger with DEPTH and RATE controls, both range from 0-10. If I wanted to make the DEPTH parameter sweep between ranges 3-6-3-and so on at a certain rate, how would I go about doing so? Some kind of an oscillator?

Just curious. Thanks!

[Ray Ivers]

Sonno,

IMO R.G. Keen's the go-to guy for this kind of thing, but as a brief overview... one setup that might work for replacing a single 3-terminal pot would be:

1) a low-frequency oscillator (LFO), driving

2) two LDR's, resistor sections connected as a 3-terminal dual-variable resistance (AKA a potentiometer :)), w/LED's biased partly on at zero LFO modulation.

This is without having the slightest idea what the circuit to be controlled is - there may be many other ways of doing it simpler in any particular effects unit, and also many circuits in which this solution might be unworkable; this is more of a 'universal' solution to LFO modulation of a pot-controlled parameter.

Ray

[Sonno]

Thanks for the reply!

Who's R.G. Keen? A member here?

And another question: What if the pot was digital?

[Steve Conner]

Ray: Isn't that the same method Mess'O'Boogers used in the Triaxis preamp?

Sonno: When you say "the pot was digital" do you mean:

It's a knob on a digital effects unit? In which case you're probably best reading the manual to see if the effects unit can be made to modulate itself in the way you want. If it can't, you could probably buy another one that'll do it.

Failing that, digital effects units often use an A/D converter to read ordinary pots, so you could probably unhook the pot wiper and apply a voltage from a LFO, but it might not be too good if the effects unit firmware only checks its pots every half second :( If it's one of those digital rotary encoders, you're screwed.

or...

It's a digital potentiometer IC in an analog circuit? In which case replace it with the LDRs Ray mentioned or whatever.

[Ray Ivers]

Steve,

Ray: Isn't that the same method Mess'O'Boogers used in the Triaxis preamp?

Yes, sure enough - that appears to be exactly what they're doing. I used one some years back, and IIRC the controls worked fine.

Ray

[Sonno]

Ray: Isn't that the same method Mess'O'Boogers used in the Triaxis preamp?

Sonno: When you say "the pot was digital" do you mean:

It's a knob on a digital effects unit? In which case you're probably best reading the manual to see if the effects unit can be made to modulate itself in the way you want. If it can't, you could probably buy another one that'll do it.

Failing that, digital effects units often use an A/D converter to read ordinary pots, so you could probably unhook the pot wiper and apply a voltage from a LFO, but it might not be too good if the effects unit firmware only checks its pots every half second :( If it's one of those digital rotary encoders, you're screwed.

or...

It's a digital potentiometer IC in an analog circuit? In which case replace it with the LDRs Ray mentioned or whatever.

That's exactly what I mean.