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let's just call it 20 hours |
Okay, then with a 200mAh battery you can only draw 10mA, and you must fully use the battery. (No clipping allowed before the end of battery life.)
You've got 1.5mA in two buffers, and another 1mA in the LED. Add another 0.5mA for small things like the TLE2426 and resistors-to-ground. That leaves 2.75mA per amplifier for the op-amp. The 3mA/ch AD8620 isn't too far over that limit, so personally I'd relax that 20 hour number to get its sound quality. The AD823 is right at our limit, but I think it'll be a bit too aggressive with those Grados. The OPA2107 is under the limit, but it's not specified for low-voltage operation, and I haven't tested one for that myself.
You'll notice that this rules out stacking buffers, the EL2002, and class A bias. You'll also notice that I left the ground buffer out; put a jumper from pin 2 to 7.
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he did NOT put a power cap on, since he said that would drastically reduce battery life |
Only if you turn the thing on and off again frequently. They do draw some power on startup, but beyond that they leak only tiny amounts of current.
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I am using the AD845 OPAMPS |
Well there you go. 10mA per amplifier, and not exactly the lowest drop-out voltage of the chips I've used. That change plus adding the ground buffer in the amp above, and you'd be lucky to get 7 hours.
As for the rest, perhaps you're stacking buffers, or using the EL2002, or biasing the op-amp into class A, or running your LED a little hot, or simply not able to run the battery all the way down before you hit the clipping point.