But why? I know iPods sounds crappy, but does that fix the issue? How long would that 9-volt last?
There are three reasons why iPods 'sound like crap':
1. The stock earbuds, which are absolute shit. I have a pair of full-sized cans (Sennheiser HD280 Pros) and a set of small clip-on style phones (Koss KSC-75). They both sound fantastic with this setup.
2. Crappy MP3 encoding. All of my stuff is ripped as WAV from my own collection, then converted to m4a lossless. Not only is it indistinguishable (to me) from the original CD, but I can burn it to disc if I need to for a bit-perfect copy of the original.
3. The iPod internal amp is mediocre. By using the line-out port instead of the headphone jack, the signal bypasses the internal amp circuitry of the iPod and provides a cleaner, more direct signal to the output source. The iPod volume control is disabled when using the line-out (since that is all done in the iPod's amp section) but the cmoy amp has a volume control so it's a non-issue.
These three things definitely fix the crappy sound issue.
That 9v battery came with the amp, I plan on getting a rechargeable 9v at some point before this one dies. People typically get 20-30 hours out of a standard 250mAh 9v battery, depending on how loud you're cranking the thing.
jperryss, is that an Arduino board/unit powering the amp?
It's actually a cmoyBB, based loosely on the
original cmoy design. This design is from John Seaber at
JDS Labs and includes a bass boost switch.