Class D Technology

Wading through this discussion, I found myself reminded of the late neurologist, Oliver Sacks. He was, as I’m sure you all know, hugely interested in music and how we experience it. He was an enthusiastic devotee of the music of Johann Sebastian Bach, and was pretty indifferent to the music of Beethoven. He volunteered for a brain-scan to see how he reacted to the music of each composer, and the results showed that Bach noticeably increased his brain’s activity, while Beethoven showed no such effect. http://mentalfloss.com/article/23288/inside-oliver-sackss-brain-he-listens-music

I mention this because what I’m taking away from this lively discourse (apart from the technical details which is mostly beyond me) is that we all have our innate preferences. A sound that lights one person’s candle might have no effect at all on another, and some of these sounds might be actively irritating to a few. Our ears and our brain-wiring are all different, so what appeals to one group of us won’t appeal to another. Hence our differing preferences for and reactions to various classes of amplification.

Personally (and I’ve alluded to this subject in my review of the Wyred4Sound reclocker, q.v.), as a professional musician, I like to be "inside" the music, that is, to be able to discern its details and building-blocks, but I still want the overall sound to be pleasing (musical) enough to be enjoyable. It’s a balancing act. As stated in my previous post in this thread, my ARC STi200 achieves this for me. It might not for you, though, which is fine. I’m not a tube-person, but I certainly can see (hear) why this sound appeals to so many of you. Would be very interesting to see what MY brain looks like on music.

atmasphere, I’ve pretty much heard it all , including Atmasphere amps.

phase shift is just one factor that might acount for an expansive soundstage. You can’t equate the two or infer a large soundstage necessarily means phase shift being heard. if its truly phase shift that is there and not being mentioned then the reviewers need to go back to school perhaps.

For example, my setup has expansive soundstage only on recordings made a certain way conducive to that. on others it is quite the opposite. So there is no evidence there of artificial effects of phase distortion that would persist constantly. Certainly nothing that I can hear with any of my speakers large or small. You might measure something but I doubt anyone could single it out listening.

Maybe young pups with 20-20khz hearing and speakers with awesome bandwidth, but frankly there is a good chance that other forms of noise and distortion are what’s mostly occurring at the highest frequencies for various reasons, phase shift being one of many nasty things that occur there predominantly. Very little music does. Mostly just "air" at 20khz.. See the reference here:

http://www.independentrecording.net/irn/resources/freqchart/main_display.ht

So based on a combo of facts and experience I still see it as one of theoretical things that exist but do not add up to much if anything in practice for most.

So based on a combo of facts and experience I still see it as one of theoretical things that exist but do not add up to much if anything in practice for most.

Are you going to be producing an amplifier anytime soon?

If an amp cuts off at 20KHz then expect phase shift artifacts down to 2KHz. If an amp cuts off at 60KHz then its 6KHz. If the cutoff has a steep slope the artifacts can be more severe. The trick, if you can't get bandwidth the way you want, is to not have a severe rolloff.

You'd think this stuff is inaudible but it isn't. Many factors add up to how a given amp sounds and its plain foolish to attempt to focus on any one factor by holding it above others **or** below. They **all** affect the result.

So you are right in a sense. But I'll give you an example of how phase shift can manifest. Years ago a dealer brought an MFA Magus preamp to me with the complaint that it was really bright in the phono section. In fact I had heard this problem in the preamp myself. I put it on the bench and  found that in the RIAA equalization there was a circuit that caused the equalization to go to flat at 50KHz. This is a ways above human hearing. Normally the RIAA curve would be rolling off at 6db per octave.

So I took the circuit out, thus restoring the RIAA curve (FWIW the RIAA  did not spec the curve past 20KHz but it usually designers assume that it will continue with its 6db per octave rolloff as frequency goes up). The **very audible** brightness was eliminated! The dealer was thrilled, and MFA changed their production so that this circuit was omitted. Apparently they didn't like the brightness either, but had not made the phase shift connection. They said it was there to "improve square wave response". I'm sure it did that!

If your amp does not have lot of bandwidth then you are in the same boat as a lot of SET owners and they seem to like their amps just fine. The fact is that its not the most important thing in the world. But don't confuse that with it not being audible at all! In a class D amp, most of the artifact that its going to have is coming from the input circuit and in that regard whatever amplification it has (probably an opamp) which imposes its own signature. That's a lot better than the signature that many transistor amps impose; opamps if treated right can be pretty musical. If the bandwidth is limited then the amp might not seem very bright and a lot of audiophiles (myself amongst them) cringe when things get too bright. You like your amp a lot so if your hearing isn't too off than I have to assume that the designer chose a reasonable set of compromises in the design. I guarantee though that the designer would prefer to work with greater bandwidth if possible. When they come out with the latest greatest replacement for your amp (which will happen sooner or later), take a look at the bandwidth spec and see if they didn't improve on it. 

Are you going to be producing an amplifier anytime soon?

Nope. Not my lot. I’m just a critical listener reporting what I hear and trying to understand why.

I already have two generations of Bel canto Class D amps. I have yet to hear any hint of brightness ever with the newer one. Even with Dynaudio Contour monitors known to lean that way with the wrong amp. It is an all in one integrated the C5i so less to get wrong or right when matching . In fact one of the reasons I bought it was to be able to compare and contrast with what I had. And guess what, better bandwidth and improvements in general with a newer and still evolving technology is exactly the thing that leads me to keep testing the waters.

As I said I do not doubt the relevance of bandwidth in theory, only is it an issue of enough magnitude in practice that most people would care these days when things are done well otherwise.

Some people report brightness in some Class D amps. Same true with other SS amps. Probably even with tube amps to a lesser degree. But I am not hearing it at all ever, in fact less than ever, with my latest and greatest Class D amp. So I do not find the fears bandied about with the technology in general to be warranted at all in practice.

Nor am I saying all Class D amps perform equally well either. Only the ones I own and know well for sure. That just proves to me it can be done now and today. I am not alone there I would say. YM always varies.

Its nice to hear a maker of tube amps and another of passive pre-amps gives the competing technology some credit. Its only fair to point out where the achilles heels lie. Every product has one. All good information for the educated consumer to mull over when making a decision.

Here is part of Lamm Industries ML3 Signature amplifier by Michael Fremer in 9/2013 Stereophile.

The ML3s produced the most glorious, palpable, airy, detailed midrange I’ve ever heard from reproduced music. That part is easy. They pushed that performance envelope without going all greasy and congealed over time, as some tube amps do after the initial appeal of warmth wears off.

The ML3’s standout features were its natural re-creation of instrumental attacks, generous sustain, and lifelike decay—all as close to live as I’ve heard, if nowhere near the real thing. It was quiet, fast, detailed, dynamic without reservation, transparent, airy, and extended on top. No sharp edges unless the recording had them, and no boredom-inducing global softening. The pair of them produced an enormous sense of space when that was appropriate, and, within that space, images of exceptional delicacy, three-dimensionality, and body.

It should be good for $140k/pair. This amplifier has measured -3dB bandwidth at about 50kHz - which is 15kHz less than my class D amp, that supposed to suffer from wrong harmonics summing. Please notice words "airy, and extended on top". Imaging also did not suffer.