Best headphone amp for new Senn 650's

Try the Musical Fidelity V3 . It is amazing! and under $ 400.00

Just my $.02 here, but since you didn't limit the price, I agree with Ed and Jim that the Cary SEI is nice. I disagree that the Earmax is next best though. I had the Earmax and it was (in my tastes and in my system) not any better that the headphone jack on my Pioner Elite CD recorder. I also have a Headroom Cosmic which easily bested the Earmax. My main headphone rig, like the Cary SEI, doubles as a very nice SET integrated - the Moth Audio SI-2A3. If you like a typical warmer but clean and detailed SET tube sound, the Moth is fabulous. If you like a little more slam then the Cosmic has more of a solid state sound and is tighter in the bass with nice dynamics.

I also had the first version of the ASL MG-Head amp and, although I liked the sound, it cannot drive the Senns to any decent volume and the Moth is much more dynamic, with better detail and focus.

If you like the tube sound, I recommend checking out the ASL OTL32 headamp/preamp or the ASL Twinhead headamp/pre or the RKV. If you want solid state, I think you'd be hard pressed to find anything better than a PPA amp, regardless of price. Several head-fi memebers said they heard a PPA amp with the HD650 at a meet and it blew away the Headroom Blockhead. So you could go with a PPA and save quite a bit of money. There are tons of amps out there, so be careful and don't lose your head over this. BTW I have the HD580 with MG Head OTL and I think it is a wonderful combo.

Sarah- the folks over at head-fi are often younger and/or really into DIY and specs. There is a lot of discussion about rolling op-amps, and how something must sound better 'cause it it has bigger tubes and heat sinks and all. Some of the serious folks there have very good ears, but there is a lot of chaff to separate out. I have not heard Singlepower, or PPA. Gilmore amps are designed by Kevin Gilmore, who is an academic type who has released several headphone amps designs into the public domain, and some of them are being "manufactured" by folks you can find on Head-fi. Each one is typically different, tweaked with diff caps, or op-amps or whatever. I agree that the RKV looks awesome, but I'venever been able to hear one. One member owns a Moth SI-2A2 and says Moth will customize those for your particular cans. He has also heard a prototype of a new amp the owner of Moth will be selling under another company name later this month for about $400, which he says is quite remarkable. I have heard one of the Emmeline amps and it was quite good but not remarkable. Email me and I'll give you the name of the guy to get more info on the new moth amp, which he auditioned with 650s, I belive.

I bought a pair of HD 600's with my Benchmark DAC-1 and am very happy with it. The benefits obviously being that for the 850.00 you get a very high quality DAC.

Rob