Ray Samuels Audio P-51 Mustang

Original Owner.  From a smoke free pet free enviornment.  Part of a stack I carried with me everywhere.  Some minor scuffs that give it loads of character, but sounds absolutely amazing!!!  Selling to fund upgraditis.
Includes Charger
Specs from Ray Samuels: 50 K input impedance. 5 ohms-300 Ohms output impedance. 250ma per channel drive capability. rail to rail input/output voltage swing. Freq. response, 5hz-100K No caps in the signal path. 72 hours of play back using IEMs from single charge. 3.7-4.2 volts Lithium ion powered Charging time about 2 hours. Dimensions... 1.5" width 2.25" length .7" height. about 4-5 Oz weight.
Review by Skylab: Ray Samuels Audio Mustang P-51
Info: P-51 Mustang – Ray Samuels Audio
I received a loaner of the new Mustang P-51 portable headphone amp from Ray Samuels Audio. The impossibly small Mustang is quite full featured – lithium Ion battery built in, 3 gain settings. Smaller even that the Tomahawk. Same styling as other RSA amps, which is to say a very attractive anodized metal case. The Mustang, according to Ray, can deliver more than 2 times the amount of current that a Tomahawk can. Pretty impressive.
Headphones used for this review were the Audio Technica AT-ESW9, Kenwood K1000, and the Sennheiser PXC-350.
Build Quality: A+: Attractive metal case, properly sized metal knob, very sturdy connectors. Doesn’t get any better.
Treble: A: Amazingly smooth and musical, and yet highly detailed. Maybe not quite as extended as the iQube, but if not, very close. Slightly more extended than the Meier 2Move. The unusual instrumentation on Joanna Newsome’s “Cosmia” was very well rendered.
Midrange: A++: OK, here it comes – the best mids of any portable headphone amp EVER. Yes, this includes the iQube, 2Move, and any of Ray’s other amps. The mids on the Mustang have to be heard to be believed. I was SHOCKED. So pretty, so lush and liquid, and yet so neutral and transparent. Joanna Newsome’s harp and voice on “Cosmia” were so good I truly got shivers and goosebumps. The Mustang’s mids are nothing short of THRILLING.
Bass: A+: Full, tight, tuneful, punchy, deep bass. RSA amps all have great bass, and this one is no exception. No bloat, but lots of meat. Really nice. Just about the perfect combination of fullness, power, and control.
Neutrality: A+: Is it just a touch warm? Probably. Does this make it sound colored? NO WAY. It sounds completely natural – maybe to a level I haven’t quite experienced.
Soundstaging: A: The soundstage was deep, wide, and very well defined. It isn’t quite as good iQube in this regard, but this still will not be seen as a shortcoming.
Transparency: A+: It’s amazingly transparent – it has a jaw-droppingly open, clear, are grain-free sound. It really excels here. Music just naturally flows out of the Mustang, in a liquid, natural way.
WOW. The Mustang is a real achievement in terms of portable headphone amps, in absolute terms, let alone for one that is so small. In fact it is hard for me to accept how such a small little headphone amp can sound so very good. But it sounds EXCELLENT. In my opinion, it is the best sounding RSA portable amp I have reviewed (I have not reviewed the SR71A Blackbird, but all the others).
The Mustang takes its place at the very top of the pyramid in the world of portable headphone amps. It’s terrific, and I cannot recommend it highly enough. For the price, at this level of quality, it’s even a bargain. It was so good, it actually required a bit of re-ranking at the top of my list.
By Skylab @ Head-fi.org.