Expanding the Class D Conversation: How Would You Characterize Their Differences?

If anyone here is surpised at the amount of tube gear at AXPONA...Keep attending future hifi shows and maybe you won’t be surprised.

Probably a good prediction. You might have missed that this is not really about surprise. We’re trying to explain it, given various circumstances mentioned in other posts. Got any theories?

And if it just so happens that your choice likes to wallow in one-ohm territory, the correct response is to buy amps that are comfortable driving one-ohm loads.

@devinplombier If you want the most out of your amplifier investment dollar, avoiding loads like this is a very good idea. All amps make more distortion driving lower impedance, which is heard as not as smooth, not as detailed (and speaker cables become for more critical!). You always want the amp to be loafing for its job, allowing it to have a lot in common with sitting on a park bench. That's when the amp, regardless of its technology, will sound its best. 

Based on what I’ve heard in my studio and what I’ve read on LAiV’s website, I am guessing the GaNM amps are operating at a sampling frequency that’s so high it does not require feedback, and as a result, current and voltage remain in phase.

@hilde45 FWIW Dept.: With this comment he really showed he didn't know what he was talking about.

Dead time is a device used in any class D amp to prevent the output section overheating and failing very quickly. It is the same amount of time needed to keep a given device (MOSFET or GaNFET) cool and does not vary with switching frequency. So when the switching frequency is higher, the dead time makes up a greater and greater portion of the pulse train- essentially increasing distortion. So you have an increasing need for feedback as switching frequency is increased. You do get more loop gain with higher switching frequencies, so its possible to have more feedback.... At any rate, the reason to use GaNFETs isn't speed so much as being able to reduce switching noise because you have far less parasitic inductance in the output section. 

To give you an idea of how much lower that noise can be, our class D is between 60 and 70dB below the value set by the EU Directives (for which you obtain the CE mark), and that is caused by the power supply rectifier in the amp rather than the output section! As a result there are a lot of tube amps (like the Dynaco ST35) that radiate more noise than our class D. Keeping noise down is vital if you want associated digital gear to work properly! 

@decooney 

But still:

• Not truly continuous like tubes or Class A

That really depends on who you talk to. I can point you to some people who say quite the opposite. FWIW. AI really can't be trusted!

Or is an audio show a bad place to read the tea leaves, at least in some respects? 

@hilde45 I think its a bad place to read the tea leaves.

That is because the musical instrument amplifier market (guitar and bass amps) consumes 90% of tubes made worldwide. Class D is now invading that market too; Fender, using the Sunn marque, has just released the Sunn Beta Lead amp, which is class D.

Since most guitar players use effects pedals to create their 'sound', all the guitar amp has to do is not be annoying. Its not like it was decades ago when Jimi Hendricks got his sound by overdriving his Marshall amps! It makes a big difference if you are waiting for the headlining act to get done with their set so your band can finally move its gear out of the venue at 3:AM, that your amp weighs 15 pounds instead of 85! So in ten years the tube market is going to look at lot different. The larger tube producers are going to have to sort out what to do when 90% of their market is moving away from them. 

 the Shuguang factory closure in 2019,

It closed because it burned down. It got rebuilt about two years ago and is producing tubes once again. 

I don't intend to stop playing with tubes since its fun. We're actually working on a tube prototype right now but I've got no illusions it will be better than our class D. But some people still can't make that leap, so we'll have something for them (that also uses tubes that will be easier to find as sources dry up). 

@atmasphere Thank you for your generous and informative replies. And your corrections!

I suppose the factory burning down helped explain a temporary shortage, but my sense is that even though it was rebuilt (the article I cited discusses an upsurge of interest in the Chinese market for tubes) there is still an overall trajectory where tubes stick around but become more and more of a niche in the market.

That "tube factory" information is way out of date about Shuguang, plant burn. A lot has happened since then too past 2-3 years. PSVANE picked up all the tooling and tube line from TJ Full Music for smaller tubes. Shuguang partner lines of tubes they've come out with since, and some of the overseas distributors have picked up these lines too. I have no affiliation with these guys, just sharing, showing. 

Shuguang-PSVANE right here: https://shuguangpsvane.com/collections/shuguang-audio-tubes

Again what I was floored about is just how many different rooms with tube amps, tube preamps, and so many other "tube" related devices after we've been led to believe its all slowing down, clearly not the case looking over all of the Axpona walk-thru videos too. 

The good news is, the audio industry seems to be alive and well after quite a few years of slow-down post pandemic. Quite a turn out this year at Axpona, new dealers, new distributors or old ones, new options - many showed up. Very cool!

@atmasphere That really depends on who you talk to. I can point you to some people who say quite the opposite. FWIW. AI really can't be trusted!

All good points taken Ralph, 10-4.  A few members and I do discuss this part, and to your valid point - that "we've gotta hear it in our room, our system, with our speakers", unquote.  

Maybe some day I'll get the chance to hear your amps on my own custom design speakers.  I was looking for Axpona videos of reviewers in your Popori / Atmasphere listening room just for fun. Saw a few quick walk-thrus, not sit-and-listen ones, not yet.  Will keep looking.  If something shows up on YT, feel free to send a message or reply here. Not like being at Axpona, but it is fun to listen to other reviewers comments and what they saw and heard first hand. Thanks Ralph!