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adding an offset pot on the CGS75 processor

adding an offset pot on the CGS75 processor

2017-01-18 by phijel

Hello


I just successfully built 3 X CGS75 in modcan A format including the processor part. And they're working great !


So I'm wondering if want to add an offset pot on the processor (only thing missing in this circuit IMHO) can I simply reproduce the CGS81 schematic using a 100K pot wired to +/-15v respectively on the CW and CCW tabs, and the wiper going to PR2 through a 270K resistor (and the 2 X BAT 48 eventually) ?


Ph

Re: adding an offset pot on the CGS75 processor

2017-01-31 by phijel

another small question related to that, if I want the offset being -5/+5v instead of -15/+15v, can I simply add a voltage divider between the offset pot and the 270K resistor ? When simulating the circuit, I found out that a 100k/62k pair seems to do the trick, but is there a better way to do this ?

Re: adding an offset pot on the CGS75 processor

2017-01-31 by Ken Stone

The 270k was chosen to give that ratio. It forms part of a divider with the 100k feedback resistor. Increase the 270k to reduce the amount of offset.
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On Wed, Feb 1, 2017 at 1:28 AM, philippe@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:

another small question related to that, if I want the offset being -5/+5v instead of -15/+15v, can I simply add a voltage divider between the offset pot and the 270K resistor ? When simulating the circuit, I found out that a 100k/62k pair seems to do the trick, but is there a better way to do this ?




--
Ken Stone otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>

Re: adding an offset pot on the CGS75 processor

2017-02-02 by phijel

Hi Ken, thanks

Oh indeed, I just checked on the one I built and I have a +/- 5v offset, but strangely when I emulate the circuit on iCircuit I have +/-15V after the 270K resistor. probably user error on my side, not really familiar with this program...

Re: adding an offset pot on the CGS75 processor

2017-02-02 by phijel

btw, (and sorry for the noob question - it's for my education) isn't one of the resistor in a voltage divider supposed to be connected to ground ? Doesn't seem to be the case here...

Re: adding an offset pot on the CGS75 processor

2017-02-02 by phijel

Thanks Ken. Oh yes, I just checked and indeed the one I built gives me a +/-5 V offset, but strangely when I simulate the circuit on iCircuit I have +/-15v after the 270k resistor. Probably user error on my side, not really familiar with this program.

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