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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
georgehifi's avatar
georgehifi
10,312 posts
 
my old class D amp had 60kHz bandwidth
Yeah and it probably looked like this on a 1khz square wave
https://cdn.head-fi.org/a/2780785.jpg
It all about how much switching noise is let through without causing phase shifts down into the audible range.
And that why 1.5mHz is good for switching frequency, because it can be filtered out well above and not have any phase shifts down into the audible frequency band, like all the others do.

Here is the Anthem Statement M1 claimed frequency response to 45khz look at it’s square wave, not pretty, in fact if you saw this on a linear amp you’d have to say it’s broken. https://www.stereophile.com/images/1212AM1fig02.jpg

Cheers George
kijanki's avatar
kijanki
4,428 posts
 
Yes 90kHz is a little better than 60 or 70kHz, but not by much - leaving noticeable phase shift in audio band. I’m not even sure that this phase lag is a problem, since speaker, being inductive at higher frequencies, shifts phase forward. Lamm Industries Signature Monoblock ML3 has only 30-40kHz bandwidth (that should introduce substantial phase shifts in audio band), but was highly praised by Stereophile: "It was quiet, fast, detailed, dynamic without reservation, transparent, airy, and extended on top".
This example suggests that it is far better to form opinion after listening to particular amp than making blank statements about whole class D.
erik_squires OP
16,021 posts
 
Thanks @melvinjames, Honestly I think it's just 30 year old biases. We might as well be complaining that solid state gear isn't as reliable as tubes again.

Best,
E
georgehifi's avatar
georgehifi
10,312 posts
 
This example suggests that it is far better to form opinion after listening to particular amp than making blank statements about whole class D.
Measurements don’t lie, there is considerable phase shifts down to 5khz if the output filter is set too low to minimise switching frequency being too high in amplitude. And if the filter is set too high the the switching frequency become very apparent riding on the back of 1k square waves. (re: the links I posted above)

The only remedy is to raise the switching frequency by at least 3-4 x and set the fiter much higher so it can do it’s job, as Technics has done to 1.5mHz with the SE-R1. And this can be done using GaN Technology.

From EPC’s Steve Collino, past inventors of the Power Mosfet and now the new GaN Technology.

"Our GaN FET will give an even higher performance difference compared with MOSFETs in both sound quality and efficiency at 1.536 MHz."

He said then, they have to be heaksinked, as Technics had to do.

Cheers George
erik_squires OP
16,021 posts
 
When I started this thread I was really worried that Goerge would have gotten too old and tired not to raise the same tired and irrelevant tropes he always does, but whatever held him back before, it's good to see he's recovered and fit as a fiddle, cutting and pasting the same things from the dozens of other threads on the subject.
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