Could anybody here modify one of the recommended portable headphone amps so that it would take it's power (not the signal!) from an USB connection and not from batteries?
As I understand USB offers a 5 Volt connection and high current needing devices can draw up to 500mA, which again might not be that high, but enough to drive most headphones.
At least META42 can be tailored below 6 Volts it seems. Porta Corda II seems to run off 9 Volts, whereas the Supermini runs off 3x1.5 Volt batteries.
I haven't measured any USB power rails, so I don't know how stable they are. Probably quite unstable at least on most computers, I'd think. This would probably necessitate further power regulation compared to an ordinary battery based setup (?).
I have a specific need for such an amp as I'm trying to build a portable amp that doesn't have to rely on batteries (or availability of wall to plug into) and will be plugged into various kinds of portable sources and computer soundcards.
The amp might have to drive phones up to 300 Ohms and quite inefficient. Specific models I have in mind (although this may change) include Sennheiser HD-250 Linear II and Beyerdynamic DT831.
Any ideas / links?
PS I could probably build it myself, but I have so much to do right now...
There are inexpensive voltage regulator chips meant specifically for this purpose (stabilizing USB power). They also have mechanisms for preventing surges into your laptop. You can also grab power from the PC card slot (PCMCIA/Cardbus) or the removable battery/hard drive/disk bay, if you have one (10-12V).
On the other hand, it might not be worth the trouble. I'm working on a USB device right now (should finish the PCB this afternoon), and I'm using wall/battery power. It's simpler.