Voltage Controlled Crossfader/VCA

[Thomas_Henry]

Hi Gang,

As promised, here is another circuit for you to play with. It can be used either as a voltage controlled crossfader or as an ordinary VCA. I hit upon this when finally realizing something that was in front of me all the time---the control currents though the voltage-to-current converter are symmetric yet opposite. It's an obvious idea once you see it and has probably been used before. But I was glad to stumble upon it.

Null out the DC thumps in the usual way. (Turn the audio inputs down, then apply a 0 to +5V square wave to the CV input.)

The usual legalese applies. Feel free to use this for personal applications but don't copy, or produce commercially. Anyone wanting to do a non-commercial PCB for EM users please contact me first.

Have fun!

Thomas Henry

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[v-un-v]

Looks fun Mr Henry! Cheers!

[inlifeindeath]

can't wait to try out the new designs thomas! thanks as always for your work!

[widdly]

Thanks for another great design Thomas.

I built it this afternoon on perf board and it works very nicely. Like the other TH designs I've built, the input ranges on all the controls are tuned perfectly.

[fonik]

while looking around for a simple crossfader CV circuitry i found a very similiar on an old tom gamble EFM dual VCA, however, your solution is much more elegant and adds a nice touch with the overall volume control using the emitters!
thank you!

[elmegil]

Excellent, thanks Thomas!

(Previous post deleted; still need the reminder not to post before finishing my tea)

[Sethkaine]

Hello Thomas,

I'm trying myself to your OTA designs : learning, breadboarding, etching, soldering, testing, listening. I love your designs from birthofsynth by the way.

Sounds great to discover "new to my knowledge" designs in this forum. I'll going to try it out.

continue the good job and a big thank you for your schematics you're pleasing my ears.

[wackelpeter]

Nice design Thomas, many thanks for that very cool circuit.

It's not only a Crossfader or VCA also some kind of manual or voltage controlled wavefolder/mangler when you feed two waveforms from one VCO into it.

Like it

Makes me feel i need a second one...

[richardc64]

And still no love for mine.

http://www.sdiy.org/richardc64/mmvca/

[LFLab]

Which IS very interesting! Have you tried this with the LM13700 schematic already, Richard?

[roglok]

[richardc64]

[wackelpeter]

[sompost]

Hi all,

I would like to use this great circuit as a voltage controlled mixer (crossfader option on sheet 1 above). Because the master level would always be set to maximum level, and envelope control would not be needed, the whole branch to the left of R11 (between Q1 and Q2) seems unnecessary for a crossfader-only use. Am I right?

What would I have to replace that branch with? Do I need the buffer (IC3c) or can I just supply +15V via some resistance to the point between Q1 and Q2? What would that resistance be?

Thanks!

[4b11b4]

[LFLab]

By the way, I have built RichardC64's version with LM13700, and it works fine.
Forgot to add capacitors to the audio inputs though, and I haven't calibrated it yet, but it does work. (let me know if you'd like a few boards Richard).

[sompost]

[richardc64]

[LFLab]

Not sure what the mystery resistor is (maybe I should read everything before plonking something in Eagle ), but this is what I have now, no wiring needed.


The lower section is one of Ray's (MFOS) VCA's.



(sorry for the OT discussion)

[richardc64]

[Cfish]

Thank you Thomas.
so much of my modular is built from your schematics. I know I can perfboard them up and count on them to work.
That always means a lot to me. Will give this one a try.

[VinL]

First post!

I've found a minor mistake in the crossfader/vca schematic. On the schematic pin 13 of the TL074 is labelled as the non-inverting input and pin 12 as the inverting input whereas it should be the opposite. I was actually building a dual version of vca-1, wich is very similar, with lm13700 and using both schematics got me stumbling on this anomaly.

BTW I love Thomas Henry designs!!! My favorites since I got into synth DIY about a year ago.

[Thomas_Henry]

Thanks for pointing that out.

To be clear, everyone, the pinout in the schem is correct, so build away! Only the plus and minus signs in the op-amp representation of IC3d are reversed.

Thomas Henry

[ReToxx]

Hello everybody,
I want to build a small circuit wich allows me to feed back the normal output and the inverted one of a filter back to its input by a voltage controlled crossfader. So i want to have a knob which has no output in its middle position,
full ccw would be the inverted only (which also means no output at the output;-) ), full cw would be the normal output. And I also want cv control over the crossfading, where the knob acts as a starting point for the cv...
I want to leave as much as possible, but I don't know how to deal with that amp stuff thats going to in between the two transistors...
I already left the ac/dc switch, and the attenuators at the inputs, as well as the dc offset trimmers, as i will use it only for audio. And i added an attenuverter at the cv in...
don't know if that all makes sense and what to do with the input at the transistor, maybe i could only leave the initial gain pot as a trimmer, but to what value do i have to trimm that? or can i somehow set a voltage right at the transistors and get rid of the opamps there...
thanks so much for any advice

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[fonik]