Just wanted to share the little headphone amp I wired up.
Cheap, portable, easy to solder, and decent quality components so it sounds great.
What you need:
1.$10 http://www.ebay.com.au/itm/2-X-150-mW-Class-AB-Headphone-Amplifier-Board-LM4881-150mW-Stereo-HP-Amp-/121155320773?pt=AU_Bedroom_Furniture&hash=item1c356b7bc5
2. 9V battery clip (a few cents)
3. Canon AV cable.
4. Suitable enclosure of your choice. Sweets tins are good.
I had a spare AV cable so I chose to butcher it and keep it simple but you could easily wire up RCA sockets. I also chose not to use terminal blocks but they're probably a good idea.
There's only a dip switch for low and high gain but I've found the default setting to be the perfect level as is.
You could easily attenuate the input with a pot but I find the ML headphone volume control is enough (devs: a couple a negative gain options might be handy)
(http://tijuanacartel.com/web/photo-1.JPG)
(http://tijuanacartel.com/web/photo-2.JPG)
Now just need a on/off switch and suitable pocket sized case that could be optionally velcro'd to the tripod.
Specs are not bad either.
Size:76.2 mm (L) x 50.8 mm (W) x 12.1 mm(H) ± 0.2mm
Thermal shutdown protection circuitry
Adjustable gain
Wide power supply range: 8V-24V
Audiophile Quality Sound:
0.025% THD+N @120mWrms 16Ω
0.02% THD+N @75mWrms 32Ω
(http://tijuanacartel.com/web/specs.png)
If you want something self-contained and smaller, check out the FiiO E06 portable headphone amplifier (http://www.amazon.co.uk/FiiO-E06-Portable-Headphone-Amplifier/dp/B005HJWWW8/ref=sr_1_1?ie=UTF8&qid=1414134436&sr=8-1&keywords=fiio+e06).
Nice. 3 x price and a bit more fiddly with extra connections, though I guess you could just solder a 3.5mm plug onto the av cable. Charging via USB is def a nice vibe though!