Time to buy a class D amp?

Hello atmasphere,

     Thank you for your very good update on your class D amp development. Very interesting, although not very surprising, that you decided to utilize GaN FETs in your design given their ultra fast switching on/off capacity which enables the elimination of dead-time and lowers distortion. I’m not sure if you discovered yet what Merrill, of Merrill Audio, stated that he has discovered: that the newer GaN transistors don’t perform as well as some of the older examples.
     I remain very interested in listening to your new class D amps in my system. I recently upgraded my system with a pre-owned Levinson 326S preamp and Magnepan 3.7i speakers. I’m currently using a pair of D-Sonic M3-600-M mono-block class D amps rated at 1,200 watts @ 4 ohms that are performing very well driving the 3.7is.
     I understand the 3.7is likely don’t require 1,200 watts to perform optimally but I believe they benefit from a ready and steady availability of high current. My issue is that I’m uncertain if 200 watts @ 4 ohms would be sufficient for them. I’m also uncertain whether there would be a net overall sound quality gain in my system by utilizing very well designed class D amps, with reduced dead-time and distortion, but perhaps less than optimum current availability. I’ll likely only find out for certain by auditioning them in my system.
     Have you made a decision yet on whether you’ll be offering free limited in-home trial periods for auditioning?

Thanks,
Tim

Have you made a decision yet on whether you’ll be offering free limited in-home trial periods for auditioning?

We're not nearly that far along!
With regards to GaN performance, they can be variable depending on who made them and their intended application. Many of them have a reverse diode conduction phase which can really throw the designer for a loop. While they are faster, MOSFETs have been steadily getting faster too so at practica switching speeds we're seeing now in another year or two MOSFETs will probably work just as well. One problem we're seeing is its very easy to build a class D with a very high damping factor, much higher than any speaker should really see.

Hello atmosphere,

      Please don't treat my occasional post questions directed to you, and your vast amp design knowledge and experience, as anything even remotely close to an attempt at rushing your class D amp design and development efforts. Of course, I understand you're going to take whatever time you deem necessary at every progression in the nuts and bolts process of creating a high quality class D amp that bears your company's well respected name.   
     My layman aim remains the same, which is just to seek out and utilize high quality system components that maximizes my music and HT listening experiences.  Having subject matter experts, such as yourself, explain things to me in an easily understood, relatable manner while educating my posterior along the way just happens to be a much appreciated bonus.  Thank you.
     For example, your concern about excessive damping factors on class D amps is something I can relate to due to experiencing its effects on my  system's performance.  I've previously driven a pair of Magnepan 2.7QR speakers in my system with three different brands/models of high powered and high damping factor class D amps, two stereo units and a pair of mono-blocks.  It was immediately very apparent to me with all three that the bass response was more prominent than with any of the numerous non-class D amps I'd previously used on these same speakers. 
      At the time, I considered this very powerful, taut, dynamic and prominent bass response the best I'd ever experienced on the 2.7QRs, that are 3-ways with a rather large 623 square inch dipole planar-magnetic bass panel section on each speaker.  However, I subsequently purchased an Audio Kinesis Debra 4-sub distributed bass array system with all four subs powered by a 1K watt class AB amp/control unit.  I continued to drive the 2.7QRs full-range (down to their rated bass extension of 35 Hz +/- 3db) with the class D amps and the 4-sub bass system was restricted to reproducing only the bass content from 20-40 Hz.  
     The bass with this setup was definitely improved in power, detail, dynamics and especially realism and naturalness.   Over time and in retrospect, I slowly became aware that while I really enjoyed the bass response solely reproduced by the class D amps and the 2.7QRs, the bass sounded much better with the AK Debra system included.  My theory is that the very high damping factors unique to class D amps was truncating the decay times of the bass notes.  The four Debra subs, being powered by a class AB amp that has a lower damping factor and did not shorten the decay times of bass notes, therefore allowing the bass to sound more realistic, detailed and natural.  Does this make sense to you?


Thanks,
  Tim

My theory is that the very high damping factors unique to class D amps was truncating the decay times of the bass notes.

IMO it is possible to overdamp loudspeakers and thus truncate the bass notes, ending up with a coloration called 'tight bass'.

In this regard, amps have outstripped loudspeakers in terms of advancing the art. What I mean by this is for an amplifier to be a true voltage source, it has to have a very low output impedance, and while most speakers (certainly not all!) are meant to be driven by a voltage source amplifier, the simple fact is that they also should not be overdamped, and most high powered solid state amps do just that. No speaker made needs more than about 20:1 as a damping factor. But we see amps that have 500:1 and more- there is no way these amps can avoid coloring the bass as a result.


IOW I agree with your observations.

The good Nelson Pass posted some interesting musings on high vs. low impedance amps and drivers and how they might be matched up here:

https://www.passdiy.com/project/amplifiers/current-source-amplifiers-and-sensitive-full-range-driver...

Fun stuff.