Self-powered USB DAC/Headphone Amp combo?

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Long time since my last post on this forum... but on to the subject.
I've used my SR80 Grados with my laptop quite a while but the headphone connector on the laptop started to die on me and it's really annoying, I always have to play with it to find the right spot...
At work I'm using a PC which has such a low output that I can easily hear all the environmental noise while using the phones (not the Grados, obviously, they're open...).
All this made me think "it'd really be nice to have a compact USB DAC with an integrated decent phone amp... portable, small, no headaches with low output sound cards or broken phone connectors...".
So... there are USB DACs like the Monica, and tons of amps schematics. Maybe someone already built such a thing? But if not...
USB normally provides 0.5 amps if I can recall correctly, maybe this wouldn't be enough? Believe me or not, but I haven't ever wondered what's the current range phones eat... Even if the 0.5 amps are not enough, external or even battery power would be an option.
What do you think?
 
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You might have a look at this:
The γ1 Modular Miniature DAC

1.5Vrms may be enough for your headphones (Grados are low impedance, I think).

If you need more than that, you'd have to look at a boost converter to get a higher voltage. I have a number of MAX3232 chips at home and was thinking of using them for this purpose, stealing the power supply normally used for the RS232 interface.

Edit: just had a quick look at the MAX3232, it only provides a +/-5.5V supply. I may consider a voltage inverter instead (e.g. 7660) to get a -5V supply.
 
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