distortionless voltage controlled resistors???

[Brian Marshall]

Ok, I'm trying transistors, Jfets, diodes.. in the audio path i just cant get rid of the distortion.  I dont really want to use optos, but it looks like i might have to.

[ocelot]

What are you talking about ?

Do you want to reduce gain ?

[gez]

Ok, I'm trying transistors, Jfets, diodes.. in the audio path i just cant get rid of the distortion.  I dont really want to use optos, but it looks like i might have to.

Keep the audio signal at such a level that distortion doesn't happen, i.e. divide down and then amplify at a later stage.

[The Tone God]

I assume that you want to vary the signal with the least amount of distortion. LDRs are best for meeting that criteria. Depending on what your doing you can modify your circuit to better reduce the distortion conditions using other devices but the safest and simplest way is an optocoupler.

Andrew

[Brian Marshall]

I assume that you want to vary the signal with the least amount of distortion. LDRs are best for meeting that criteria. Depending on what your doing you can modify your circuit to better reduce the distortion conditions using other devices but the safest and simplest way is an optocoupler.

Andrew

yeah, i guess that's just the answer that i didnt want to hear

I am trying to control a somewhat unconventional filter circuit.  unfortunately, i think because the resistance in question is in the feedback loop of an opamp any minor amount of distortion is severely amplified.  I have the input signal so low in the circuit.  i dont think i can make the signal any smaller at this point.  I've got some optos on order... but dont know when they will get there.

[Paul Perry (Frostwave)]

i think because the resistance in question is in the feedback loop of an opamp any minor amount of distortion is severely amplified.  

I don't think it makes any difference, whether the non-linear resistor is in the input or the feedback path, so far as distortion is concerned.
The only completely linear 'variable resistor' that I know of, is one that is PWM switched at ultrasonic frequencies. Hard to get enough range, though, in my experience.

[puretube]

you checked the OTA app-notes yet? (3080; 3094; 3280; 13600; 13700?)

[Tim Escobedo]

OTAs might be good, if they don't require you to completely redesign the circuit. Other than that, Vactrols are the easiest, most practical answer i've found.  

[Brian Marshall]

i think because the resistance in question is in the feedback loop of an opamp any minor amount of distortion is severely amplified.  

I don't think it makes any difference, whether the non-linear resistor is in the input or the feedback path, so far as distortion is concerned.
The only completely linear 'variable resistor' that I know of, is one that is PWM switched at ultrasonic frequencies. Hard to get enough range, though, in my experience.

I was actually considering doing something like this, but the parts count on it might make it not so worthwhile in the end.

[Brian Marshall]

you checked the OTA app-notes yet? (3080; 3094; 3280; 13600; 13700?)

dont ota's have the same limitations as transistors?  or do they sort of self regulate themselves.  I dont own any OTA's to play arround with right now.  maybe in a few weeks ill order some up.

One of my considerations when designing something for comercial use is the idea of using common parts between products.