GaN-based Class D power amps

Nope, it’s inherent in a lot of Class D. It doesn’t work quite the same way though. Some uses local feedback, which does not include the output, and some do.

Feedback and a triangle wave oscillator is how the analog input is converted to PWM output.

Class D does not have to use feedback.

PWM (pulse width modulation) does not use any feedback at all.

In a switching amplifier you have something called 'propagation delay'. This is a time delay caused by the fact that it takes a while for a device to switch on or off. Put a number of devices one after the other and there can be a quite measurable delay from input to output.

For this reason NFB taken from the output and applied to the input will always be slightly out of sync with the signal its supposed to correct. For this reason it will add distortion of its own. Fortunately class D amps don't have to use feedback to have low distortion.

+1, Ralph, for educating and keeping us on track!

Ok, time for me to clean up some ignorant commentary expressed in one of my posts on this page. The Lyngdorf amp is a class D amp, but not one that includes GaN-FET transistors (+1, bulldogger). The amp might be a modified Bruno Putzeys’ design using variants of his Hypex Ncore modules (+1, GeorgeHiFi) with judicious use of NFB across the audio frequency spectrum. Bruno Putzeys is the person I believe Lyngdorf mentioned in his FB post. By searching "Bruno Putzeys," I discovered he is also the designer behind a class D monoblock called Mola Mola Kaluga. At $16k per monoblock pair, it was said to be competitive price-wise and sonically with the best amps out there.

Some reviews are here:

https://www.soundstagehifi.com/index.php/equipment-reviews/972-mola-mola-kaluga-mono-amplifiershttps://www.6moons.com/audioreviews2/molamola/1.html

It remains to be seen whether Bruno will migrate to GaN-FET tech class D designs, but this amp isn’t one of them. It will be interesting to A/B this class D design against the best sounding GaN-FET class D amps out there (whatever that may be).

It was stated earlier in this thread that "there are no truly digital amplifiers".

This is very wrong. They’ve been out for 20 years -starting with the TacT Millennium in 1998 and reviewed (that year) by Robert Greene of The Absolute Sound.

Wadia had their PowerDAC right after, but it was never reviewed and only had a 3-year life.

The TacT was re-branded under Lyngdorf Audio. It has been joined by the NAD M32 and Technics R1 - the only 3 in the world I’m aware of. (Another from Italy, was ’blogged’ by Clement Perry of Stereo Times, but was never reviewed).

Though they have diff. methods of attenuating the signal, they all share the same (basic) topology -a DAC-integrated w/o separate sections. Meaning NO analog stages, NO converters. The switching output stage acts as a D to A.

What’s shocking in 2019 is how few audiophiles are aware of this revolutionary product category. There are reviews in the past 5 years, starting with Jim Merod in PFO (reviewing NAD’s M2 back then).

So it’s catching on, one decade at a time...