hello Peter,
thank you for the usefull info!
but,
i think, by using vactrols, he means by adding the
universal vactrol module A101-9. this should make the
vactrol mod much easier, i guess.
but it would probably require on more 4HP faceplate to
add the vactrol input. or not
best regards,
Bakis.


--- "(i think you can figure that out)"
< peter@... > wrote:

> You shouldn't need a vactrol at all. There is a
> current limiting 100K
> resistor coming from the wiper (center pin) of the
> Freq pot. That's
> the only place the wiper goes, this 100K resistor
> should be easy to
> locate. One end of that resistor goes to the wiper,
> the other end goes
> to one of the negative inputs of the two opamps.
> That means either
> pins 2, 6, 9 or 13. That's the first thing you have
> to find. So you
> buzz out and find the 100K resistor that goes to the
> center pin of the
> Freq pot, go across the other side of that resistor
> and buzz out which
> IC and which pin (2, 6, 9 or 13) that side shorts
> to.
>
> Once you find point where the other side of the
> 100K goes to either
> of the two op amp ICs at either pins 2, 6, 9, or
> 13...then stop
> looking. That's the one you need.
>
> Add your VC Input jack to the faceplate, run it's
> output to another
> resitor you'll need to add (another current limiter,
> start at 100K and
> work down until you're happy with the response, but
> try not to go
> lower than 47K), and connect the output of that
> added resistor to the
> node of the PCB mentioned above. So you run the
> output of your
> resistor to the other end of the resistor on the
> Dopefer PCB which
> comes from the wiper of their Freq pot.
>
> That should do it.
>
> You can add a attenuation pot if you wish as well
> (if there's room for
> both the jack and the added pot on the faceplate,
> not sure if there is):
>
> In that case, the output of the jack you add goes to
> one of the end
> pins of the added pot the other end pin of that pot
> is connected to
> ground. The wiper of the added pot (the center
> pin)is connected to the
> current limiter resistor you just added which I
> explained in the last
> paragraph.
>
> If you attenuator works in inverse (less FM when
> turning the pot CW),
> then reverse the wires coming from it's two end
> pins.
>
> Not sure how the expo converter works on this
> particular LFO, so you
> may not get linear VC response, and most definately
> not 1v/oct, but
> this mod should work OK.
>
> Yes you could do it by added a vactrol, but that
> would require cuts
> traces on the LFO PCB, a bunch of discrete
> components to drive the
> vactrol LED, and the VAC itself. Basically another
> board will be
> required. It would be more prudent just to buy a
> Doepfer VC LFO in my
> opinion.
>
> It's worth a skipping all that and trying this
> first.
>
> - P
>
>
> --- In Doepfer_a100@yahoogroups.com , Anthony Rolando
> <goldenechos@...>
> wrote:
> >
> >
> > I would like to add Voltage control to my A-145
> LFO. I would like to
> do so with a Vactrol. Would anybody be willing to
> point me in the
> right direction
> >
> > Would it be possible that I could look at a
> portion of the schematic
> so that I could add this
> >
> > Thanx,
> >
> > Tony
> >
>

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>

Bakis Sirros - Parallel Worlds / Interconnected / Memory Geist
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