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From: Morris Slutsky on 9 Aug 2010 23:20
For some years I've had a transformer, bridge rectifier, and large
electrolytic caps from some sort of power supply rescued out of
scientific garbage, because I couldn't bear to see it discarded, and I
never really figured out what to do with a 30 V supply that could
maybe do 1-2A judging by the size of the transformer. Not big enough
for a huge audio amp.

I often listen to music on my computer and am frustrated by the
pitiful headroom of the built in headphone output. It's actually
impossible to listen to anything with more dynamics than pop music
because if the quiet passages are audible, the loud ones are
distorted. I bet it runs off the +5 motherboard supply and just
doesn't have any volts to spare.

Anyway here's an idea I had tonight - the incredibly self-indulgent
class A headphone amp. Single channel schematic shown:

http://yfrog.com/28miniphonep

At least in simulation, looks linear, plenty of gain and clean
headroom. Totally discrete for that awesome point-to-point
buildability should I choose to do so. 300 mA idle current to suffice
the lowest-impedance 32 ohm pair of earbuds out there, and an easy 20
V p-p swing for the 600 ohm console phones out there. Wonder, though,
if this is just going to be some monstrous huge thing that blows out
phones and eardrums. Yeah, it's a bit big. But for some reason I am
so tempted to build it.

Phones reference to Vcc and not to ground because the PSRR is just a
whole lot better that way. At the risk, of course, of some idiot
connecting the headphone output to a grounded input jack and creating
smoke. It'd probably have a fuse in it if I built it.

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