I was at a local surplus store today and I got two LM386N ICs. I thought I could make a really simple headphone amp out of these. But I have no idea what the wattage of a normal headphone amp is.
These LM386 are rated 325 mW at 8 Ohm, which should be about 81.25 mW at 32 Ohm load.
Is 81.25 mW a reasonable power for a headphone amp? How does that compare to, say, a Laptop's 3.5 mm jack's power; how about an iPhone's?
Best Answer
Alfred already explained that for a voltage source (which an amplifier is) you'll have less power at higher impedance, because the current decreases. If your amplifier would be a current amplifier you would get a higher power, because the same current in a higher impedance will increase voltage.
Citing from this document, because I can't explain it better myself:
(emphasis by me)
Thanks to marketing numbers of 100 W amplifiers most people don't realize this, but 1 W is a lot of power for a good speaker. It can give you more than 90 dB SPL at 1 m. At full power a 100 W amplifier just won't break the windows. Claiming to play 2000 W at full power in your living room is nothing to brag about: it just says that you have lousy speakers :-). 2000 W in 92 dB speakers delivers 125 dB SPL, which will turn you deaf in no time. (That may be OK, once you're deaf it also stops hurting your ears. :-)
Further reading
Understanding headphone power requirements