Class D is just Dandy!

I just spent the last hour catching up on this entire thread.

@erik_squires
Well done, my friend! You’ve navigated a wonderfully positive thread.

@georgehifi
Great contributions throughout. I very much would like to have seen the YouTube videos from EPC regarding their new class D modules for audio applications. Alas, they were blackened out on my iPhone. But I did enjoy your shares about new Gn-based transistors having higher switching frequencies. And your Aussie round table thread from high-end designers was special. Erik might complain about your rain, but it’s welcomed by me, as it seeks to clarify where the class D tech needs to improve. The opinion of Nelson Pass is a good benchmark to base all future commentary. 😂

@atmasphere
And yes, the motivation for class D amplification was all about increasing dynamic headroom—avoiding clipping. Yet, as @atmasphere will point out, it’s the first Watt that matters the most and where the class D tech really needs to focus.

As a teenager, I auditioned an Infinity SWAMP, which was a class D amp the late John Ulrick designed and based upon tech that John and Infinity was awarded a US Patent for. I bought a Digital One amp from Spectron Audio (apparently now defunct) in 1997 or thereabouts. I spoke with John numerous times about his topologies over the years. He said the SWAMP design was ahead of its time because the high speed switching transistors really didn’t exist during the 1970’s to make the amp stable. That all improved later in the 1990’s. He later told me in ~2006 or thereabouts that John Dunlavy used the Spectron amps to voice his SC series of Dunlavy speakers. He said that my SCIVa’s mated with the Spectron amp was a magical combination. I only saw one post here from a contributor who had a Musician III amp.

So my question is: how do the Spectron amps stack up in the mix of present class D amp technology? Back in the day, it was a 300WPC 8-Ohm) stereo amp at $2500. I’d appreciate personal accounts rather than speculation.

—Dan

P.S. Here is a link that is a tribute to John:

https://www.stereophile.com/content/john-ulrick

Pretty sure the Dunlavy SC’s didn’t vary much at all from the Duntech speakers. The SC’s have a nice impedance response (6-ohms). The Spectron Musician III amp has a fairly low output impedance (< 0.1-ohms) and a high damping factor (500:1). 

Nice amps, George.

@erik_squires

As is the case with most of what we are taught as our understanding, we must be willing to surrender our understanding to gain insight into truth. There will always be those who refuse to surrender their understanding to learn truths. And that’s ok. We just need to acknowledge it for what it is. 

@georgehifi

I understood your input to me as not trashing class D designs, per se. They differ among themselves as much as designs within categories of other topologies do. Sometimes the output devices (in this case—for our discussion—Duntech and Dunlavy SC speakers can reveal and distinguish those designs as being better matched over others, whether class D or class AB (tubes, for example). 

Even folks here who rave about their preferred designs within the class D family would concede that point. Their raves are within a given reference context. 

@tweak1
+1, my friend. I suspect some type of class A-class D hybrid will likely be the future for all class D topologies. 

+1, atmasphere.