Atma-Sphere Class D… Amazing
Today I picked up my Atma-Sphere Class D Amps. These aren’t broken in yet. And they are simply amazing. I’ve listen to a lot of High End Class D. Some that cost many times what Atma-Sphere Class D costs. I wasn’t a fan of any of them. But these amps are amazing. I really expected to hate them. So my expectations were low. The Details are of what I’ve never heard from any other amps. They are extremely neutral. To say the realism is is extremely good is a gross understatement. They are so transparent it’s scary. These amps just grab you and suck you into the music. After I live with them some and get them broken in. And do some comparisons to some other high end Amps Solid State, Tubes and Class D’s, also in other systems I’ll do a more comprehensive review. But for now, these are simply amazing amps.. Congrats to Ralph and his team. You guys nailed on these.
I’ll let you in on a secret. Use Non-magnetic stainless bolts and then you don’t have to go thru all that. A regular steel bolt heats up because its a magnetic resistance to the transformer and typically runs hotter than the transformer itself! Change it out to stainless and the transformer draws less power and runs cooler- and may well put out a slightly higher voltage. But FWIW due to the high amount of feedback, the class D has a lot of power supply noise (and voltage sag) rejection. Class D amps running less feedback will benefit more on this account.
Anyone doing this is really asking for trouble! To start with any manufacturer would void the warranty in a heartbeat. It also doesn’t go down well unless you live in a mancave wearing cargo shorts and no hope of a date :) ... if you get my drift
This is a really Bad Idea. In our case there’s an AC filter on the backside of the IEC connector (the amp in the video is from the first production prototype run). If this isn’t present, there could be noise issues. In our amp, the rectifiers in the power supply are the main source of noise and we did a lot to snub them, but the noise filter was added to really make it silent. In this way it puts out less noise on the AC line than most tube amps. You could change out the fuse but I think you’ll find that due to the large amount of feedback, the minuscule voltage drop across the fuse will have no effect whatsoever.
Here’s another thing I’ll let you in on. What is important in opamps is something called Gain Bandwidth Product. If you have enough to support the feedback in the circuit, there will be no ’sound’ of the opamps other than noise (and in our case the noise floor of the amp is mostly from the opamps). Back in the 1960s and well into the 1980s opamps did have a ’sound’ which is why if you have to change out an opamp in a vintage guitar effects pedal, its important to find an exact replacement or the pedal won’t sound right (guitar players are quite picky about that sort of thing!). Our input buffer has a gain of 2, which is to say there’s a lot of feedback and with modern opamps, as long as you don’t ask more than about 20dB or so, they will be as neutral as you can get. A friend of mine designed one of the higher performance discreet opamps out there (back when it was still worth it) and he’ll be one of the first to tell you what I did above. IOW doing something like this will result in no benefit whatsoever. To design a class D amp you can’t just wing it by plopping parts in; you have to do the math and understand the engineering behind it.
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