Originally Posted by tangent
I guess you're asking about the C2 cap voltage ratings and such? Rate those for the highest voltage they will ever see. If you're hacking some kind of external charging circuit into this, beware that this will have to put a higher voltage across the battery than their highest off-charger voltage.
Tangent, thanks for all you help and designing a much loved amp. I was not concerned about C2 voltage, I plan to use 25v caps here. And the charge circuit I have for the lipo pack ensures that the voltage never exceeds the max volt per cell for li-pos (4.2v), so 16.8 is max, and the circuit also cuts the current flow round 12v (3v per cell) to avoid cell damage.
What I was asking about was a safe yet unrestrictive (buffer current/audio quality wise) resistor velue to use for R11, as the V+ is dynamic, using your simple formula of 667xV+ will provide a range of resistor values. safest bet is to use a larger resistance to limmit current to 300ma at full voltage, but, if i understand it correctly, this will limmit the current at nominal voltages. I realise this is splitting hiars, as 300ma is WAY more current than will likelly ever be needed. But in e an effort not to hamper the performance, im wondering if the buffer can take momentary current surges of over 300ma (within reason). So, pick a R11 resistance that allows a full 300ma at 12v, and should the output be shorted (witch it most likely will at some point) the momentary >300ma surge wont hurt anything. You stated somewhere that the chip can handle higher momentary currents, so I am thinking it is not a huge deal....
Again I am splitting hairs here i think. As for the resistor dilemma I was facing (out of stock on some of the good resistors in the proper schem values), I found your wonderfull resistor calculator! so I can substitute more common and "in stock" values, and it only changes the gain by a tiny bit. But with that in mind, i have made up my mind to build 2 Pimetas, 1 lower gain for portable use (thinking a gain of 3-4) and a higher gain for home use with full sized cans.