No, I was talking about adding VC without the A101-9. My suitcase is full!

Peter, thank you VERY much for the detailed info. I really appreciate it.

Funny I was just about to start breadboarding a driver circuit for the Vactrol solution... but like Peter said, "...It would be more prudent just to buy a VCLFO..."

Been spending more time Building Sound lately, and I'd like to keep it that way!

Thanx again to all who replied,

Tony



----------------------------------------

> To: Doepfer_a100@yahoogroups.com
> From: synth_freak_2000@...
> Date: Sat, 5 Jan 2008 02:23:08 -0800
> Subject: Re: 1 Re: adding CV to A-145 LFO
>
> 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)"
> 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
>>
>> 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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