I just received a pair of Sennheiser HD 650s. Unfortunately, I have no setup to go with them--just a run-of-the-mill desktop and laptop which no special sound cards or anything else fancy. So my question is (a) what amp should I buy and (b) is there anything else I need to do in order to get good sound from these headphones? I'd really like not to spend more than $100 or so, unless that's crazy, and I'm happy to buy used if that'll get me more bang for my buck. If it matters, I listen to a pretty wide range of music but classical is at the top of the list, so I'd like to optimize for that. Finally, I'm going to be out of town from the beginning of June until late August, so I'd lean in the direction of a portable amp I can take with me for the summer, if I wouldn't be compromising quality too much by that choice.
Any advice is much appreciated. Thanks in advance!