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

toetapaudio:
"@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,
        Tim

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.  

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.

This is so correct, but so far it seems that only one has utilized this ability to take the higher switching speed up to 1.5mHz available with GaN (2.5 x higher than present), and that is Technics with their SE-R1, it does mean they had to use heatsinks to get it.

Also it’s not that the higher switching speed alone make for the good sound it gets, it’s also that the "low order output switching noise filter" that all Class-D’s have to use, can now also be taken up 2.5 x higher, this then has no effects now down into the audible range, like the filters today do, which can cause phase shifts down to 5khz, and why many complain about something not right in the upper mids/highs.

Cheers George

Also it’s not that the higher switching speed alone make for the good sound it gets, it’s also that the "low order output switching noise filter" that all Class-D’s have to use, can now also be taken up 2.5 x higher, this then has no effects now down into the audible range, like the filters today do, which can cause phase shifts down to 5khz, and why many complain about something not right in the upper mids/highs.

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.