This is a lot of amplifier for the money. It's big and heavy and impressively filled with functional bits, and it houses some genuinely novel technology.
The principal designer behind the 840A is Doug Self. His books on audio design reveal an admirable ability to research and innovate. His stated aim is to produce amplifiers with such low levels of departure from perfection they could reasonably be called 'blameless'.
As his research has shown, the best route to this is Class A amplification, but the practical downside of this approach is high power consumption. So, he developed 'Class XD', reducing the effects of crossover distortion in a Class AB amp to very near the levels found in true Class A. It's still not quite as power-efficient as Class AB, but sounds superb.
The heart of the 840A is a vast mains transformer, surrounded by heatsinks, to which are attached the several power transistors required to make Class XD work well. A line-only amp, but there's plenty going on with relay selection of inputs.
There are also more relays adjusting volume in 1dB steps, by switching resistors in and out - it may be purist but it's mechanically noisy when you adjust the volume! Build quality is good, with decent components throughout. The front panel display, though not exactly beautiful, gives clear information on what's selected.
As sometimes happens, some of our listeners' comments seemed rather at odds with each other when it came to the 840A. They agreed on some areas, though, including a slightly treble-rich balance. Interestingly, none of them ever actually described it as 'bright', but all felt that the treble was strongly presented.
At the same time, suggested one of them, the sound managed to be a little slower than with some of the amps in the group. This isn't necessarily a contradiction in terms as strong treble badly timed could easily make an amp seem slow.
But timing was felt on the whole to be good. On the other hand, the treble wasn't to everyone's liking, being described as 'glassy' in one track. That's hardly a potent criticism, but it does highlight the fact that the treble was clearly more present than the group average.
The bass, however, did properly divide opinion. One listener found it weak, another well extended. Surely it can't be both? Perhaps the key lies in the comment that deep bass is good but upper bass to midrange is less so. Depending on which region your own ear is best attuned to (not to mention the music playing), the overall bass performance will - in that case - seem more or less impressive.
Dynamics attracted favourable comment, and from our own listening we would agree that they manage to be wide but sufficiently effortless not to dominate one's perception of the sound. 'Overstated' dynamics can be wearing as they are usually a symptom of roughness at high levels, and there's no trace of that here.
In addition, detail is good at all playback levels. While our last test of the amp produced an arguably more uniform positive response, there's still plenty to recommend it from this outing.