Though if i was going to buy an amp would this Fiio £30 model do the job :-
http://www.ebay.co.uk/itm/FiiO-E-6-mini-amp-PORTABLE-AUDIO-amplifier-E6-4-Headphone-Earphone-MP3-mp-3-/251245182385?pt=UK_CE_MP3Access_RL&hash=item3a7f613db1#ht_3438wt_1142