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.


But even with an digital source built into the amp, its still an analog process.

There are people who are going to argue all audio amplifiers are by definition, analog, but we don’t call DAC’s analog either.

If an amp samples the input into discrete voltages, at regular intervals (i.e. has a sampling rate) and has an output controlled by those inputs, even if the last stage has an analog feedback loop, then it is 95% digital, and the last part had an analog feedback loop I call bunk on those who want to insist that makes the whole amp analog.  Calling it a digital amplifier is a lot closer to the truth than calling an analog amp.

Calling it a digital amplifier is a lot closer to the truth than calling an analog amp.
Amplification process is still analog, hence "Analog Amplifier".  Connecting amplifier to DAC doesn't make amplification "digital".
"@noble100, f.y.i. In a recent test of various class D amps by someone we know in the business GAN amps did not come out top but were pretty high up. The other D amps were cheaper. My advice stick with your NC1200 module amps."

  Hello toetap,

    Sorry about the delay in responding, I had stopped following this thread but just checked back.
     I've haven't heard a class D amp using the newer GaN transistors yet, I've just read some very positive reviews on a few amps using them.  I'm not an electrical engineer or amp designer but it still makes a lot of sense  to me that these very fast switching transistors are likely to only improve the performance of any device they're deployed in. 
      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.  I would imagine that any good amp designer would believe that substituting these for the typical FETs used would result in significant improvements in the sound quality of any class D amps, or really any solid-state amps, that they're utilized in.  
     I'd prefer to personally compare some good class D amps using GaN transistors to my current D-Sonic M3-600-M class D monoblocs, which actually utilize Abletec ALC-1200-1300 and not Hypex NC1200 class D power modules, before passing judgement on their sound quality performance.  I'm willing to pay more if I perceive these new class D amps as sounding significantly better 

Thanks for the info,
Calling it a digital amplifier is a lot closer to the truth than calling an analog amp.
Not if you talk to a designer of a class D amp :)

Switching is a bit different from digital. Digital has bits with which meaning (a sound signal) is imposed- how many bits are on or off and in what combination carries the meaning. The switching of a class D amp does not. Instead, it switches according to its encoding scheme. Gain is not represented by how many bits are on or off, gain is instead produced by the encoding scheme, for example in a Pulse Width Modulation scheme the gain is essentially the difference of the triangle wave vs the input signal. Thus it is possible to vary the gain of the amp by changing the amplitude of the triangle wave. This is fundamentally different from digital!
When class D amp is switching between two discrete levels not the voltage but duty cycle is a quantity of interest and it is linear (no discrete steps).  It becomes converted back to corresponding voltage thru averaging (filtering).  Voltage gain of such amp is a function of switched voltage amplitude.