Cgs synth

To answer the question, you would need a DUAL op amp. You described an
inverting buffer with a gain of 3.3. So if you put +5V into it, you
would get -16.5V out theoretically. But you can't ever get more that
about 14.5V positive or negative from an op amp with +/-15V power
supplies. I would recommend a 100K/270K ratio. The second op amp would
reinvert this at unity gain 100K/100K.

If you look at the schematic for my Mixer/Comparator, you get a better
picture. That module can multiply an input x2 if you put the same
signal into both MIX 1 and MIX 2 inputs.

http://www.pugix.com/mixer-comparator.htm

Make sure you get the 2006 version schematic.

-Richard Brewster

Jeff Foster wrote:

>hi folks,
>This is OT from CGS, although related being that the modules are
>used :-) I have a basic fundamental question which will reflect my
>less than ideal foundation in electroinc design.
>
>I have a pro one synth (first synth bought, still going after 25
>years) and I like to modulate the vcf from other voltage sources. The
>vcf cv input looks like it wants 0-15v, based on the schematic.
>
>Most of the voltages I have for sweeps and random modulations are 0 to
>5v. My question is will a simple opamp with a 100k input resistor and
>a 330k feedback resistor provide the nessary voltage gain to drive the
>vcf to its full range? I found several voltagr processing DIY circuits
>on the web, but none seem to amplife the voltage, only add an off set
>amount or mix voltages. Could I add a pot in an output buffer of one
>of thess designs to get overall voltage gain?
>
>thanks for any suggestions.
>Jeff
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>The CGS Modular Synth home page: http://www.cgs.synth.net/
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>Yahoo! Groups Links
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