FYI, all of the current Luxman integrated amps are AB with some having a larger biased operating range for Class A.
The 550AXII and 590AXII have the higher Class A operating range, but they do transition to AB for higher ouputs (even though you don’t see that specified).
I confirmed this with Luxman USA directly - here is their email reply
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The Luxman L-550aXII integrated amplifier is rated by Luxman at 20 watt RMS per channel, while operating in Class-A into 8 Ohms. Above 20 watts, the L-550aXII amplifier transitions to Class AB based on the output stage biasing scheme applied.
For impedances below 8 Ohms or above, the Class-A envelope of operation is reduced, as again operation transitions to class AB. For it’s rated 20+20 watts RMS measured at 8 ohms, it is a “pure class-A” integrated amplifier. Other power specs remain unlisted on Luxman’s website because the designed-in amplifier headroom is simply fact. Also, most 20+20 watt RMS transistor amplifiers don’t weigh 24.3 kilos.
Background:
Over the decades, Luxman has produced a variety of Class-A power amplifiers and Class-A capable integrated amplifiers. Not all models were produced for North American sales or ever seen here.
In the past, it was acceptable to build (electrically inefficient) 50+ watt/channel, pure Class-A amplifiers. To offset the considerable heat produced during Class-A operation, specialized chassis constructions were incorporating using liquid coolant filled “heat-pipes” and or cooling fan(s).
Electrical consumption was such that for some Luxman models, two AC power cable connections were required; one for each (stereo) channel. (i.e. M-05) These earlier Class-A developments began in the 1970’s, in the all analog sources era.
AM/FM radio, phonograph records, cassette tape, open reel tape, 8-track etc. were largely the only (consumer) available music sources. And all these sources had at least one aspect in common; limited dynamic range. An amplifier supplier then (Yamaha, Pioneer, Luxman etc.) could build a 25+25 watt Class-A amplifier without much concern for dynamic headroom or loudspeaker load tolerance with the dynamic range of digital audio sources unknown.
Enter digital; beginning with CD and today…with SACD and HD file downloads. Modern digital audio sources demand much greater performance and dynamic headroom from today’s generation of amplifiers. Enter as well, global environmental concerns, and global power generation/ electrical grid concerns. We now have un-avoidable “Energy Star” ratings for most North American electrical appliances efficiency. And appliance energy efficiency is of great concern throughout the rest of the world. While not heard loudly at the moment, amplifier manufacturer’s worldwide are more and more incorporating high efficiency digital amplification. (i.e. Class -D, ICEpower, HYPEX etc.) This trend will speed up in the years ahead as inefficient amplification will be further frowned upon by various world government electrical certification bodies.
Luxman anticipated these actions and decided some years ago to implement pure Class-A designs which gradually transition to AB at accommodate dynamic headroom demands of today’s digital audio sources. Simply put, Luxman engineers believed this was the best compromise. (for efficiency too) It preserves sound quality without resorting to (generally inferior sounding) digital amplification to keep the amplifier away from clipping. In this way, it is also factual that the Luxman L-550aXII produces near 70 watts RMS/CH into 8 Ohms before clipping onset.
For most musical content, playing digital (or analog) sources at moderate levels in a residential listening environment, the L-550aXII or L-590aXII will operate mostly within their Class-A envelope. Music crescendos or loud transients will instantaneously demand brief bursts of increased power. It will be during those few milliseconds that Luxman L-550aXII and L590aXII will be operating in AB. The process is imperceptible. Luxman is not alone with A/AB circuits acting like this. Another example is the recently reviewed PASS INT-25.
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The 550 and 590 actually have a max output of 70watts/8-ohms.
The L-505uXII, L-507uXII, and L-509X are also Class A but only for the first 6 watts, then go AB to their rated outputs.
