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I went from Class D to Luxman A/AB - And most of what you think is wrong

Hi everyone,

As most of you know, I’m a fan of Class D. I have lived with ICEPower 250AS based amps for a couple of years. Before that I lived with a pair of Parasound A21s (for HT) and now I’m listening to a Luxman 507ux.


I have some thoughts after long term listening:
  • The tropes of Class D having particularly bad, noticeable Class D qualities are all wrong and have been for years.
  • No one has ever heard my Class D amps and gone: "Oh, wow, Class D, that’s why I hate it."
  • The Luxman is a better amp than my ICEPower modules, which are already pretty old.

I found the Class D a touch warm, powerful, noise free. Blindfolded I cannot tell them apart from the Parasound A21s which are completely linear, and run a touch warm due to high Class A operation, and VERY similar in power output.


The Luxman 507 beats them both, but no amp stands out as nasty sounding or lacking in the ability to be musical and involving.


What the Luxman 507 does better is in the midrange and ends of the spectrum. It is less dark, sweeter in the midrange, and sounds more powerful, almost "louder" in the sense of having more treble and bass. It IS a better amplifier than I had before. Imaging is about the same.


There was one significant operational difference, which others have confirmed. I don't know why this is true, but the Class D amps needed 2-4 days to warm up. The Luxman needs no time at all. I have no rational, engineering explanation for this. After leaving the ICEPower amps off for a weekend, they sounded pretty low fi. Took 2 days to come back. I can come home after work and turn the Luxman on and it sounds great from the first moment.


Please keep this in mind when evaluating.


Best,

E
erik_squires
atmasphere's avatar
atmasphere
11,772 posts
 
For example, I’ve read that GaN transistors are capable of switching so fast they literally eliminate dead-time and any resulting distortion caused by it.

If a designer believes that, its simply because the encoding scheme and related parts are slow enough that the circuit may not need any dedicated deadtime circuitry since its literally built in due to those slower parts.  Or- the designer added enough heatsinks so that the GaN devices stay cool even though there is shoot-through current.

Your need to go on ad nauseum without actually addressing the points I made is actually kind of like watching a fetish in public.
What point did I not address?

jmolsberg's avatar
jmolsberg
467 posts
 
@toetapaudio, I would love to audition those brands. I firmly believe class D will be the norm sooner than later. I heard the mola’s a couple times, at audio shows, which is far from perfect for listening.

teo_audio
2,197 posts
 
That’s true, but it might open another bag of worms. In current designs filter leaves about 1% of switching noise on the speaker cable. It is only small percentage but of very high value, reaching 100V - making it approx. 1V peak switching noise on the cable. It can be easily seen with the scope. The only reason why it does not radiate is the fact that 500kHz wavelength is 600m. Antena becomes very ineffective below 1/10 of the wavelength - in this case 60m. There will be still some, very small electromagnetic radiation but it should not be a problem. Increasing switching frequency, let say 10x will make this antena "dangerous" at 6m, producing some radiation even with regular speaker cables. It is possible to filter it better, but it would lower bandwidth resulting in phase shift in audio band, that we want to avoid. Perhaps compromise is somewhere in-between, increasing switching frequency only 2-3x while still enjoying improved linearity thru reduction of dead time.
I can hear that residual noise as a forming of hash and noise around every single transient, micro transient and complex harmonic.

Basically, class d loses the idea of high fidelity as all of high fidelity happens in that exact spot mentioned. the rest of the signal is almost meaningless.

So i spend a lifetime trying to fix that tiny little bit and class D comes along and maims to death the very part I and other in the realm of high fidelity seek and fight for.

This noise can be mistaken by some people as detail, when it is actually noise and out of band, out of time ---- added distortion and noise.

worst of all, in the modern realm of digital audio, A/D and D/ A systems also cause massive disturbance right in this area of signal.

This means you now have an entire generation of people who have NO IDEA how good analog can sound and generally does sound, when this part that digital does wrong, is absent in the signal.

Then, this lack of knowledge and exposure to what analog does right, is then aided and abetted by the hash and junk that Class D adds in on top of that. this whole mess is somehow regarded as muddy and fatiguing ’detail’, where it all sounds the same. Because it is.

this is like some freaking nightmare world. You’re kidding me, right?
georgehifi's avatar
georgehifi
10,312 posts
 
That’s true, but it might open another bag of worms. In current designs filter leaves about 1% of switching noise on the speaker cable.
As you say "it might"
You’ll just have to look at what Technics did on the SE-R1, no complaints about it becoming an RF transmitter using normal non shielded speaker cable, just praise for it's good sound.
Maybe they’ve done some fancy RF output filter as you can see (orange) the amplitude and cycles of ringing are much reduced as well the square wave itself is far better.
https://ibb.co/MpmqzGt

Cheers George
kijanki's avatar
kijanki
4,428 posts
 
You’ll just have to look at what Technics did on the SE-R1, no complaints about it becoming an RF transmitter using normal non shielded speaker cable, just praise for it's good sound.
Perhaps because they raised frequency response only to 90kHz, implying about 50% increase in switching frequency (my old class D amp had 60kHz bandwidth).  They could go higher with GaN Mosfets but stopped at only 90kHz possibly because of RF radiation.  Rowland's integrated Daemon has 70kHz bandwidth at 10x more output power (1500WPC @ 8ohm).  AFAIK it uses plain non-GaN Mosfets.
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