Lab Series compressor LED - change polarity?

[aion]

I'm working on a stripped-down version of the Lab Series preamp that uses a charge pump instead of the AC voltage multiplier.

Current requirements should be fairly low overall, but one thing I wanted to do in this version was to change the compression limit LED so it runs off of the +V rail instead of the -V rail. Here is the schematic -



(The LED is at the bottom, along with Q2 and Q3)

The -V rail is a lot less stable than the +V rail since it's generated by the charge pump, so I didn't want to stress that rail any more than necessary with an LED that would suck a few mA on a variable basis.

Is there an easy way to make the LED go from positive to ground instead of from ground to -V without significantly changing the actual compressor portion of the circuit?

[PRR]

With the 680r resistor it could be sucking 12mA, probably 11mA more than is needed. 10k instead may be ample light with far less load.

The next obvious step is a PNP transistor to switch current from the + rail. Since all the current in a '3080 is proportional to I(abc), you can tap at the + rail.

[aion]

The next obvious step is a PNP transistor to switch current from the + rail. Since all the current in a '3080 is proportional to I(abc), you can tap at the + rail.

I should have mentioned that I'm switching to the LM13700 for this version since there is another CA3080 earlier in the circuit, so I am guessing that trick would not work?

Could it be as simple as putting the CLR to +V instead of ground, and the Q5 emitter to ground instead of -V?

[PRR]

> Q5 emitter to ground instead of -V?

Draw it out.

No, because you are sensing voltage on Iabc relative to V-. Sensing from ground, Q5 won't come on.