So I received the A70 and 10A supply from Amazon. Hooked it up to one channel of my system, the other powered by a hypex nc400 monoblock I constructed years ago, having paid careful attention to its potentially problematic inputs w/r/t RF interference and the lack of adequate RF rejection (which can alias against the switching frequency of the hypex), and also using RF-rejecting XLR interconnects i built. I've never actually A/B'd this amp to see if it sounds as good and clean as I've been used to for years.
I was prepared to be disappointed that the nc400's were going to sound exactly the same as this cheap amplifier. But that is absolutely not the case. The nc400 sounds significantly, night-and-day better. Bass is slammier and punchier and properly beefy like I expected it to be. The bass on the A70 sounds much thinner, slower, and less substantial than the other channel. The Hypex highs sound clearer and audiofilier, while the A70 has a bit of a class-D car-stereo or class-D boombox feel -- slightly grittier highs. Overall it sound like I'm listening through a fog or haze on the A70 while the Hypex is crystal clear sounding.
Now obviously everybody's going to say it's psychological, as I must be in some kind of love relationship with my hand-assembled carefully routed and length-minimized and power-twisted cabling soldered to connectors on the monoblocks. That may be true, in which case. it's the best damn placebo effect ever!
I used the balance on RME ADI-2 PRO FS R to switch between amplifiers. The level on the A70 is significantly lower than the NC400, so you have to volume adjust, which I did by ear, but I guess I can be scientific by looking up the amplification level of the NC400 versus A70 -- anybody have those figures handy?
So once I do that (or just use my phone as a level meter), I can make a final determination if the significant difference I can hear is more than just a bad level adjustment on my part. [[And I just double-checked that I didn't do this A/B-ing and level-adjusting with RME's "loudness" enabled -- it was off -- because that would have explained why the bass sounded so much better on the hypex. But no -- it's real -- the bass on the Hypex is proper, and on the A70 it is thin, slow, and doesn't slam.
But right now I guess this what a brand-new SOTA mass-consumer class-D amp sounds like, and I significantly prefer my old Hypex. Just wanted to report an initial reaction.
So now I get to decide whether this is good enough for my bedroom system, where maybe I won't care about depth and slamminess of bass? Or do I return it via Amazon and try something else?
Hey
@amirm -- any chance you can test slew-rate on these amplifiers or show what a 20-60 Hz square wave looks like into a reactive load? Likewise, that's a more interesting thing to measure, IMHO, when op-amp rolling. For example the
LME49720 replaces the NE5532 with higher slew rate. I wonder if that would sound different, even if steady-state measurements end up being nearly the same -- which is as expected because of the general theoretical property of op-amps and feedback in control circuits. But music isn't a steady-state sine-wave, and the performance of op-amps with real world signals and potentially reactive loads is much different from theory and assumptions of infinite bandwidth and infinite speed-of-light (e.g. ringing). For example a faster "better" op-amp could potentially induce ringing that wouldn't be seen in a more pedestrian circuit. So it's possible "drop in" op amp rolling may produce non-optimal results as ringing compensation circuitry would need to be tuned to a specific op-amp's gain-bandwidth and gain-bandwidth-flatness:
https://www.analog.com/media/en/training-seminars/tutorials/MT-045.pdf
Thus the request for a low-frequency square wave.
Also wondering how many capacitors are in the signal-path on the A70 -- because the bass sounds like it's not DC-coupled, unlike the rest of my system (RME ADI-2 PRO FS R --> Hypex NC400). Note the Hypex spec sheet says: "To achieve optimal signal coupling, the
audio signal inputs are all DC coupled." That IMHO is why the bass on the original system sounds proper and the A70 sounds like a capacitor. I specifically selected a DC-coupled system because I hate the sound of capacitors in the signal path (other than a speaker crossover where it doesn't matter because it's feeding the tweeter).
