[sdiy] CV-vactrol circuit

Neil Johnson neil.johnson71 at gmail.com
Fri Jul 3 23:52:29 CEST 2015


Looking at the TR-9090 schematics on Trevor's website you've got an
interesting project there.
Some pots are used as variable resistors, so those would be quite easy
to automate assuming you can find vactrols with the same resistance
range.
Pots that are used as potentiometers are a trickier depending on the
exact circuit.  Experimentation might be required.
You might also have fun matching the linear CV range to the required
pot's linear or log curves.

Neil

On 3 July 2015 at 21:58,  <niroke at tampabay.rr.com> wrote:
> 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!
>
> Thanks,
>
> Nick
>
>
> ---- Tom Bugs <admin at bugbrand.co.uk> wrote:
>> Synthrotek or elby (I think) have off-the-shelf vactrol PCBs
> http://www.synthrotek.com/products/other-circuits/vac-pak/vac-pak-schematic/
> Maybe it wasn't elby.. can't remember who now..
>
> Anyways - do you really need to use (the sloppy, wide-ranging, crap of)
> vactrols?
> Do it properly with a VCA if possible!
>
> Tom
>
> 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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