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<div> Opamp A1 is connected so the current through the 100k and 300k resistors from the CV and initial control pots, as long as it is positive, is going into pin 5 of the CA3080, controlling the VCA gain.</div>
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<div>At 5V on the CV input, with the pot fully open, the current through the 100k resistor is 0.5mA (I assume this will get full gain).</div>
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<div>With the "initial gain" pot set to the top, the same current of 0.5mA is added, so the maximum current is 1mA (the absolute maximum value for the CA3080 is 2mA so this is still safe).</div>
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<div>Now if the control voltage varies from from, say, -2.5 to +2.5V (LFO output), you would set the "initial gain" pot wiper to 7.5V, so the current can vary between 0 and 0.5mA.</div>
<div>Or you could set the initial gain pot anywhere between 0V and 15V, and reduce the control voltage, to get an initial pan somewhere between X and Y and have it modulated around that point.</div>
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<div>If the control voltage range is from 0 to 5V (envelope generator) you would set the "initial gain" pot wiper to 0V to get a range between 0 and 0.5mA.</div>
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<div>To be able to do the above, the mystery resistor at the initial gain pot should be the same resistance as the pot. In practice you should make it a little smaller to deal with control voltage offsets and supply rail asymmetry, or compose it from a fixed resistor and a smaller trimpot so you can adjust it. </div>
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<div>Best regards</div>
Simon.</div>
<div><br>> Op 23 januari 2016 om 10:53 schreef Tom Wiltshire <tom@electricdruid.net>:<br>> <br>> <br>> Yep, exactly. But what that lower limit should be, I have no idea without trying it.<br>> <br>> On 23 Jan 2016, at 09:26, "Matthias Herrmann" <matthias.herrmann@fonik.de> wrote:<br>> <br>> > the resistor below the initial control will just limit the pot, no?<br>> > <br>> >> -----Ursprüngliche Nachricht-----<br>> >> Von: Synth-diy [mailto:synth-diy-bounces@dropmix.xs4all.nl] Im Auftrag von<br>> >> Tom Wiltshire<br>> >> Gesendet: Samstag, 23. Januar 2016 10:20<br>> >> An: Joe<br>> >> Cc: synth DIY<br>> >> Betreff: Re: [sdiy] panning vca<br>> >> <br>> >> Hi Joe,<br>> >> <br>> >> 100K input pots are typical, although with the 200K/100K input resistors,<br>> >> the taper will get somewhat distorted. X and Y would usually be Log (signal<br>> >> inputs) and CV would be Lin, as would the initial control. The DC trimmer<br>> >> could be 100K too, since it's feeding a 1M resistor to provide a touch of<br>> >> offset cancellation.<br>> >> <br>> >> That resistor below the initial control I have no idea about. You'll have<br>> >> to build it and see.<br>> >> <br>> >> HTH,<br>> >> Tom<br>> >> <br>> >> <br>> >> On 22 Jan 2016, at 21:13, Joe <joe.frey@radioles.com> wrote:<br>> >> <br>> >>> I am planning on building this single as a panning VCA by Richard<br>> >>> Curcio.<br>> >>> <br>> >>> http://www.sdiy.org/richardc64/mmvca/index.html<br>> >>> <br>> >>> I can source a CA3080 and since I am only building one I am not worried<br>> >>> about expense. Here's the thing, I don't know what pot values to use for<br>> >>> the trimmers and I am definitely thrown by the current controlling DC<br>> >>> trimmer, though I understand how to wire it. Can anyone take a minute(or<br>> >>> few) to help me figure them out? Thanks, Joe.<br>> >>> <br>> >>> _______________________________________________<br>> >>> Synth-diy mailing list<br>> >>> Synth-diy@dropmix.xs4all.nl<br>> >>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy<br>> >> <br>> >> _______________________________________________<br>> >> Synth-diy mailing list<br>> >> Synth-diy@dropmix.xs4all.nl<br>> >> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy<br>> > <br>> <br>> _______________________________________________<br>> Synth-diy mailing list<br>> Synth-diy@dropmix.xs4all.nl<br>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy</div></body></html>