When I first plugged into the P-51 I wasn't quite sure if I liked it. I'd been so used to a certain sound that anything different was... well different. I've spent probably a total of 4-5 hours over the last two days using my UE-11, D5000, and PK-1 and I still have some more time I'd like to put in before I draw any final conclusions but I have enough to form an opinion.
I think the most obvious thing for me with this amp is its attack. The P-51 has a very well defined attack in that the initial strike of each note from any instrument or voice is sharp and has exceptional definition as it suddenly appears from a black background. Percussion instruments sound very snappy, very much like they would sound live scenario without any unnatural decay or bleeding into what should be a black background, much less other notes. They isolate themselves very well in their own space.
The vocal presentation is somewhat forward which I think is the proper way to have it as any live show I've been to with good sound the vocals are always in the forward focus. Female vocals sound particularly sweet, the P-52 seems to capture an edge of the female voice that can often be easily glossed over or simply presented in a way that sounds soft when compared to how they sound live. Another thing that the midrange does very well is guitar tones. Guitar tones sound extremely lively and posses a body that is once again very much what one would hear at a live show with accurate energy and decay.
The top end has impressive extension and is well defined with plenty of sparkle. I did not hear an ounce of sibilance nor did I notice anything being overly splashy, again it just sounded tight and accurate. Bass is similar to other RSA amps, it is well defined, has impressive extension, and plenty of impact.
All in all I was very impressed with this amp and felt that it had a lot of energy and does a lot of things very well. The soundstage did sound a bit closed in compared to my Pico and I also preferred the way in which the Pico captures the tone of certain stringed instruments such as violins and cellos. The P-51 would be my amp of choice for female vocals, rock/country/metal while I would opt for my Pico for classical, larger jazz ensembles, and some female vocals. The review was not meant to be a comparison but I know someone would ask so there you have it. Bottom line is if I had no amp and was looking for a portable I would be content with either or maybe both
Music used for this demo:
Pink Martini - Hey Eugene! & Hang On Little Tomato
Brad Paisley - Time Well Wasted
Mudvayne - L.D. 50
Allison Krauss - Live
The Ditty Bops - Summer Rains
Hilary Hahn - Shönberg / Sibelius: Violin Concertos