"The soundstage, depending on the recording, was huge in width and cavernous in depth, with reduced surface noise and silent backgrounds." -Steve Folberg L-550AXII review
The Luxman L-550 is amber metered, indicating it's a Luxman pure class A design. It's the little brother to the L-590 and an excellent choice if class A sound is a priority at a lower price point. By comparison, the L-590 has more power, lower distortion, and a more advanced preamp section.
The L-550 has 20 watts of power into 8 Ohms, doubling to 40 watts into 4 Ohms which in the real-world of playing music at normal daily levels, and in normal sized living rooms is actually just fine, especially with the stout power supply providing torque to the presentation.
Sonically it's a sweet sounding, discrete little amplifier with a warm and liquid heart of gold. It's easy to love and perfect for those who don't want to get into the cost, size and heat of its larger brother the L-590. It's similar is size and price to the blue-metered class a/b L-505 and L-507, but in a pure class A design. If you love solo vocals and natural instruments, favor the L-550. If you like higher volumes, rock music and dynamics or have a larger room/speaker, then look to the L-505/L-507.