SET Lovers, what's the one solid state amp you love(d)?

Ralph, I was recommending your GaN amp elsewhere on this site, but his speakers do drop below 4 Ohms I think in the upper bass range, but there are no specs I can find for your amp if it’s stable down to 2 Ohms and what the power output would be (same for AGD amps BTW).  Could you maybe elaborate on that a bit here?

@soix @hedwigstheme 

A simple drop below 4 Ohms should not bother any class D amp made. 

Our class D will drive 1 Ohm. The protection circuit will simply kick in if the current is too high for the amp. FWIW, a 1 Ohm load isn't practical for any real-world speaker (although you do see impedances like that in the upper octave of some ESLs, which is not a problem). The reason is that at that impedance, the speaker cable becomes an enormous problem in terms of source impedance! This will severely limit the length of the cable and for that matter, decent cable choices available. All amplifiers made will also have higher distortion driving such a load. That distortion will be audible as less detailed and likely harsher sound since the distortion will obscure low level detail and add higher ordered harmonics which are perceived as harshness.

IOW, you can, but why??

@soix https://www.epifani.com/ makes some interesting bass amps. Powerful and quite lightweight with some heavy hitters playing with them. You can see where this is going...

Would you say that in your experience with Class D speaker matching is easier or more difficult?

Compared to a tube amp, easier! Most speakers are designed to be 'voltage driven' which is to say that the amplifier is supposed to be a 'voltage source'. A voltage source will put out the same voltage regardless of the load. To do that a very low output impedance is required. This is stupid easy with class D and difficult at best with tubes, so in theory a class D amp should be a lot easier to match with a speaker. There are limits, such as extremely low impedances which will reduce the Q of the output section filter in a class D amp, but its pretty well-known that tube amps don't like really low impedances either so that's pretty well moot.

The only exception might be ESLs. Some ESLs, like Sound Labs, have a pretty significant impedance peak in the bass, and expect the amplifier to be able to make the same power into that peak as it might in the mids and highs where the impedance is much lower. In general a voltage source doubles power as the load impedance is cut in half which also means that the output power is cut in half as the load impedance is doubled. IOW a voltage source might have its 8 Ohms power cut in half or in quarter with such speakers (Sound Labs have a 30 Ohm peak in the bass region). So tube amps can work out well on such speakers where a powerful solid state amp won't be able to make power.

In addition, the capacitive load of ESLs can mess with class D amps that are not of the 'self oscillating' variety. This is because the capacitance of the load is in parallel with the inductance of the output filter of the amp, setting up an electrical resonance which can result in ultrasonic oscillation. I know of at least one respected class D amp that suffers this trait and can fail in this application (with possible damage to the speaker as well if not properly protected). Our class D is self-oscillating and so does not have this problem.

In your case with exciting class-D amp success, does this somehow suggest you are eventually planning on shutting down your tube amp manufacturing side of the business, i.e. "are on life support"?

@decooney That depends on sales. But if we can make a class D sound as good as tubes I suspect others can too. But there are other issues that anyone dealing with tube amps should think about. We all know about the war, which has increased tube prices worldwide.

But there is also the fact that class D is making its way into the guitar world. I'm not talking about those cheap 'modeling' amps either- but good quality class D amps, often with a tube input section. They might make 50 to 200 Watts and weigh under 20 pounds. Many guitar players these days do not rely on the overdrive sound of their amps for their unique 'sound'; they get that from their effect pedals instead. So a guitar amplifier these days doesn't have to be a 100 Watt Marshall.

Its happening slowly right now. But as more class D product makes it into the guitar world, tube sales in that market will dwindle. Audiophiles may not realize it, but tube sales worldwide are driven by the guitar market, not the home audio market. In ten years I suspect the guitar world will look a lot different- if you have a 50 Watt guitar amp, its a big deal that it might weigh only 15 pounds instead of 75!!

I replaced my tube amps with a class D amp and no downside in my system- its just as smooth and revealing as the tubes were- no harshness or brightness and good bass impact. I'm really convinced that tube power amplifiers are on life support; why have one when you can have an amp that sounds better in every way and not have to deal with tube issues??