[sdiy] CV-vactrol circuit

niroke at tampabay.rr.com niroke at tampabay.rr.com
Fri Jul 3 22:58:51 CEST 2015

I'm trying to add external control to my TR-9090's voice parameters, and I'm sure if that was as simple as patching in to a CV summing point, it would have been done by now.  The 909 circuits don't lend themselves to voltage control.  From what I know, I can control the parameters with a vactrol in series with the variable resistor.  If you have a better solution, I'm eager to hear it! 



---- Tom Bugs <admin at bugbrand.co.uk> wrote: 
> Synthrotek or elby (I think) have off-the-shelf vactrol PCBs
Maybe it wasn't elby.. can't remember who now..

Anyways - do you really need to use (the sloppy, wide-ranging, crap of) 
Do it properly with a VCA if possible!


On 03/07/2015 20:45, niroke at tampabay.rr.com wrote:
> Thanks for all your replies so far, so glad to actually get through to the list from my phone!
> To be more clear, I'm not looking for any vactrol circuit and I'm not trying to build an LPG/phaser/filter.... All I'm trying to do is add voltage control over a variable resistor.  The circuit just needs 0-5V CV input, range and scale trimmers so that I can fine tune each vactrol for the required range, an amp stage (not sure why, tbh), and the Vactrol.... There are a few other bits and bobs in this circuit I've used, and unfortunately I'm not an EE so I can't learn enough from looking at this circuit to go and design something original.   I was hoping there was an old Electronotes circuit that was specifically drawn to perform this task that I could use which would be free from any IP claim.  Of course, something that old may not be as good as something made with modern components.   I admit that this circuit uses an amp IC that I've never heard of or seen used before, and there must be some significance to that.
> Nick
> ---- Julien Delgoulet <jdelgoulet at free.fr> wrote:
>> Alain as one on his moog param eq clone. Just ask him ...
>> http://www.acxsynth.com/parameq/parameqfr.htm
>> Le 3 juil. 2015 à 19:40, <niroke at tampabay.rr.com> a écrit :
>>> Can anyone direct me to a CV-Vactrol circuit which I can build and make for others which is not bound by any legal restriction?
>>> I foolishly resigned a currently-available product to suit my needs and for my own use.  I wound up having extra boards made because of a mistake on the first batch (well, there's a mistake on the second batch too), so I have more than I can use.  I wanted to be able to give them away to people building the same project.  I have now asked the manufacturer of the circuit I copied for permission to use the boards, cite him as the origin, and give the extra boards away, and have offered to collect some remuneration as a royalty.  I have not yet had a response, but I figure I should prepare for the worst, and will completely understand if that designer will feel cheated out of income for his IP.
>>> I already have the schematics, two factory modules, and permission to build clones of Doepfer's discontinued A-101-9 universal vactrol module, but that circuit is a bit more involved than necessary.  Also, I was only given the schematics and permission on the condition that I never share them or build for others.  I'd prefer to use a circuit that I can make available to other builders.
>>> Anyone one recall a suitable circuit that's free to use?
>>> Thanks,
>>> Nick
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