Help feedback Cv design

[Waronheaven]

Hello everyone, im re designing a schematic i did for a pedal while ago that has feedback and since im making it eurorack i was thinking to add cv over the feedback, any idea how to do it or any designs i can have a look at? i was wondering about LM13700 in the feedbackpath?

here is my feedback loop control.

[guest]

you could try replacing R2 with an LM13700 and see how it goes. it will definitely give you control over the feedback loop, im just not sure if it will sound exactly the same as having the pot turned.

[Waronheaven]

you could try replacing R2 with an LM13700 and see how it goes. it will definitely give you control over the feedback loop, im just not sure if it will sound exactly the same as having the pot turned.

this way is working fine.
now i would love to set min and max in order to give smaller rabge with offsets but not sure how to do that LOL

[guest]

i think im a little confused here, did you want to maintain the distortion characteristics of your original 4049 circuit, or are you replacing all that with opamps.

[guest]

also, you will want a resistor from the OP7 output to the LM13700 to limit the voltage excursions at the LM13700 input.

[guest]

i think the above deisgn will just distort when there isnt enough control current. why not something more like this:
https://tinyurl.com/2f53avnr

[Waronheaven]

i think im a little confused here, did you want to maintain the distortion characteristics of your original 4049 circuit, or are you replacing all that with opamps.

im using op amps and not hex inverters just because im not trying to simulate the clipping stage but only the control opver the cv also and cant find 4049 on ltspice, the resistor after OP7 is definetely needed, i dont understand the falstad schematic, where is it the feedback path? and the clipping stage and the cv control over the feddback?

[guest]

heres feedback and with CV control, but with the opamps its just going to saturate once you apply a small amount of positive feedback.
https://tinyurl.com/2mv4w4qr

your highpass filter in your original helps with this a bit, and that wouldnt be too hard to replicate.

[guest]

this gets closer, but it would probably be best to build up a prototype to see how it actually worked with the 4069.
https://tinyurl.com/2r3hjdap

[Waronheaven]

this gets closer, but it would probably be best to build up a prototype to see how it actually worked with the 4069.
https://tinyurl.com/2r3hjdap

What about using a tanh limiter to control the feedback path, was reading that could work and can be done also with an lm13700 (seems to be the same inside the chip) but not sure ups to do that

[guest]

its all comes down to how you want it to sound. the positive feedback is going to create some wierd sounds, and probably oscillations, so its hard to predict without trying it out.

[Waronheaven]

its all comes down to how you want it to sound. the positive feedback is going to create some wierd sounds, and probably oscillations, so its hard to predict without trying it out.

Yeah I wanted to avoid to have the usual oscillator type of sound that is characteristic of the simple feedback path design (same as my original design)

[guest]

well, thats the difficult bit. positive feedback always causes oscillations (or at least once it goes past a certain threshold). below that threshold its quite similar to adding more gain in the forward path. i have an amp that uses positive feedback, and there are some interesting sonics i can get out of it as it transitions between these two thresholds, but its quite fiddly.

[Waronheaven]

well, thats the difficult bit. positive feedback always causes oscillations (or at least once it goes past a certain threshold). below that threshold its quite similar to adding more gain in the forward path. i have an amp that uses positive feedback, and there are some interesting sonics i can get out of it as it transitions between these two thresholds, but its quite fiddly.

How would you do it if you would have used a tanh limiter with the lm13700 in the feedback path? Just to understand… a guy I know used it in his feedback path and sounds great all he said is you need limiter first and to use the other lm13700 as a limiter using fixed voltage to set the point,

[guest]

this does tanh. there is a slider for increasing the input amplitude to get the distortion:
https://tinyurl.com/2fbznn6z

[guest]

alternatively, you can control amplitude and distortion in one go if you use the linearization diodes:
https://tinyurl.com/2f4knzbn

[Waronheaven]

this does tanh. there is a slider for increasing the input amplitude to get the distortion:
https://tinyurl.com/2fbznn6z

im a bit confised here still dont understsnd your falstad design (tanh) where its supposed to go. inside the feedback path?

[guest]

yes, it goes in the feedback loop, sort of like in this one:
https://tinyurl.com/2r3hjdap

[Waronheaven]

yes, it goes in the feedback loop, sort of like in this one:
https://tinyurl.com/2r3hjdap

looks to work just fine to me, i have few questions here tho: isnt the op amo needed to be grounded in order to work?
also i have tried to make the same schematic on ltspice but somehow i cannot see the feedback signal summed back to the op amp (im also not using a non inverted amp but is doing the same thing with your design)

[guest]

i dont think i understand the question in regards to the opamp needing to be grounded. do you mean as you have it grounded in your schematic? as that is correct for an inverting configuration.

the capacitor coupling the ota signal is not going to work very well. you either need to send the current into the summing node directly, or put a resistor at the ota output to convert the current into a voltage first, then pass it through the capacitor. also, the way you have it set up, its negative feedback, as the opamp output goes to the noninverting pin.

[Waronheaven]

i dont think i understand the question in regards to the opamp needing to be grounded. do you mean as you have it grounded in your schematic? as that is correct for an inverting configuration.

the capacitor coupling the ota signal is not going to work very well. you either need to send the current into the summing node directly, or put a resistor at the ota output to convert the current into a voltage first, then pass it through the capacitor. also, the way you have it set up, its negative feedback, as the opamp output goes to the noninverting pin.

Ok sorry isn’t your configuration a non inverting op amp? I thought so, so I was wondering why the negative pin isn’t grounded.
I was wondering the best way to have the feedback as you did but using inverting amp and clipping it into the feedback path of the op amp.

[guest]

for that one i used a differential amplifier design, so signals go to both the positive and negative. i did this to have a high input impedance for the ota output.

[guest]

the inverting version looks like this:
https://tinyurl.com/2m6tssv2

[Waronheaven]

the inverting version looks like this:
https://tinyurl.com/2m6tssv2

ok gotcha, never used a differential op amp dweiogn before so i wasnt sure, i guess ill have to breadboard this to see what sounds best.
still no idea why i cannot see both signals summed on the op amop on lt spice