I've had my A90 for a week now and thought I'd post some impressions.
Build: I think the appeal of something like the A90 is not really its build quality and aesthetics. But I wanted to post some comments because I see a fair few posters saying the build quality is great. IMO it’s not. It’s very average. The case is metal, but it’s the most plastic-y metal I’ve ever seen. It’s destroyed by Schiit amps. So bear that in mind if build and aesthetics matter to you.
The volume knob is pretty bad too. The A90 knob is only marginally better than the SP200 knob, if at all. The turn is loose and imprecise and it feels cheap. Again the Schiit knobs destroy it.
Sound quality: I personally find it much easier and more useful to discuss SQ relative to comparable amps, so...
A90 v SP200
I half expected this comparison to be very close. I really wanted something with pre-outs and so any SQ improvement was going to be a bonus. But the A90 is significantly better in every way. Better detail retrieval, imaging, sound stage, balance. Tonally they’re broadly similar, although the SP200 has a honky mid/upper bass bloat I hadn’t really noticed until putting it against the A90. The A90 is flatter, more neutral. I think the price difference is justified by the performance of the two.
A90 v Jotunheim
This is a tricky comparison because these two are polar opposites. The A90 is balanced, flat, airy and laid back. The Jot is dynamic, meaty, aggressive and intimate. The Jot is more mid forward, the A90 is dead flat. In technical terms, I think the A90 is probably the better amp. It has better detail retrieval, separation, 3-D, sound stage and balance. But it is very slightly cold/clinical/digital sounding. The Jot has a beautiful rich and natural timbre to it that I prefer to the A90. The slight coldness of the A90 make it slightly less forgiving than the Jot and it can sound a touch splashy on some recordings. I do want to make it clear though that these negatives are very, very slight. Because these amps are so different, AB-ing them exaggerates these qualities. But I think it’s worth pointing them out because if you’re particularly sensitive to them it could matter to you.
I’m keeping both the Jot and A90. My Jot has the MB card and I use it in the bedroom. If I could only keep one, it would be the A90. But there is a magic to the Jot I’d miss. An amp that combined the a90s technical performance with the Jot’s timbre would be my end game I suspect it exists but is a level up in price range