[sdiy] Serge CV input circuit?

[Scott Gravenhorst]

What page is this schematic on?  I drew this out and 
it doesn't seem to me that it will do what is required
as I understand it.  (which is that at one extreme of
the pot rotation, the signal is full amplitude and
positive sign.  In the middle, output is zero.  At the
opposite extreme, amplitude is again maximum, but
the sign is negative.)

This is a rough estimate of what I believe will work:


                          A
               +------\/\/\/\/\---+
               |                  |
               |   |\             |
               |   | \            |
               |   |  \           |
               +---| - \          |
               |   |    \         |
               |   |     \        |
               /   |      \       |
               \   |       \      |
               /   |        \     |
 *---/\/\/\--->\   |         >----+--->
input          /   |        /     output
               \   |       /
               /   |      /
               |   |     /
               |   |    /
               +---| + /
               |   |  /
               |   | /
               |   |/
               |   
               |
               \
               /
               \
               / B
               \
               /
               |
               |
              GND

This should work if all resistors are the same value,
eg: 50K.  Resistors A and B could be increased to
increase the DC gain.


BrightBoy <jdec at mindspring.com> wrote:
>> Serges have on their CV inputs a circuit with a level
>> control that at center gives zero output, turn the
>> control ccw for negative modulation, cw for positive
>> modulation.
>
>(1) Take the input signal to a 50k resistor.
>(2) Take the other side of this 50k resistor to the (-) input.
>(3) Wire another 50k resistor between the (-) input and the output.
>(4) Make sure these two 50k resistors match to 0.1% for optimal
>    performance.
>(5) Take the input signal into the top of a 50k pot
>(6) Wire the bottom of this pot to ground
>(7) Take the wiper of this pot to the (+) input.
>
>You should probably go out and buy the classic op-amp book,
>"IC Op-Amp Cookbook" by Walter Jung (Sams Publishing)
>
>This is where I got the circuit from....
>
>Cheers,
>
>Jeff

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