[sdiy] Coping with diode drop(s) on Iabc input with LM13700/CA3080
chris at chrismusic.de
Wed Sep 30 14:17:08 CEST 2020
What about putting a diode drop in the OTA's V-, so that the driving amp
doesn't need to go down to the *PSU* V- ?
Or would that be too filthy?
I remember seeing this to raise a fixed voltage regulator a bit.
On Wed, 30 Sep 2020 11:53:00 +0100 Tom Wiltshire <tom at electricdruid.net>
> Hi All,
> Iâd like a bit of advice, please.
> Iâve got a 0-5V control voltage from one of my PIC LFO chips. Iâd like to use that to control a OTA-based VCA running on a 0-9V single supply.
> The typical current source circuits I know are no good for this as they would require the op-amp to operate close to the rails with the 0V CV. Just using a resistor to the Iabc input isnât an option since the lowest CV values will do nothing (the wonât overcome the diode-drop, or two on the LM13700).
> I spent a day running LTspice sims of various other methods I culled from various stompbox schematics and synths, but didnât come up with anything that seemed to work effectively.
> How should I drive the Iabc input for best linearity in this situation?
> Any guidance would be much appreciated.
> Electric Druid
> Synth & Stompbox DIY
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