Class D and High Efficiency Speakers?

09-18-08: Audiofeil
I can't think of a good reason to use class d amps with horns unless you're the adventorous type.

IMO you'd lose much of the "warmth" without the tubes.

Borrow some digital amps and give a listen. It may be your cup of tea.

But don't form your opinion until you give a listen to the ridiculously affordable Onkyo A-9555. Onkyo's design has some patented circuits to specifically address the problem of switching noise in class D amps.

Robert Deutsch reviewed the A-9555 for Stereophile into a pair of very high sensitivity Avantgarde Acoustics Uno horn speakers. He makes special mention of how he often has to chase down hum and buzzes when reviewing upstream electronics because of the Avantgarde's sensitivity. When he hooked up the Onkyo, however, he asked himself, "Is it on?" It was. So unlike most, it can be a good match for horns. And its power rating should be a good match as well.

Unlike pretty much any other class D on the planet, *once it's broken in,* the Onkyo is known for a relaxed presentation and a smooth, engaging treble. Even the little summary blurb in S'phile's Recommended Components section compares the Onkyo's *resolution of low level detail* to tube amps.

I have one and have to agree. It reminds me of the high priced class A/AB amps (Ayre, earlier Rowland) more than anything, and replaced two highly regarded vintage amps--the Amber Series 70 and VSP Labs Trans Mos 150.

Another thing: Class D amps require the best, cleanest power you can feed them. Some reviews I've read say it's like listening to two different amps, depending on the power cord used, and which, if any, power conditioner it's plugged into.

In the case of the Onkyo, after it broke in, it sounded smooth, but also dead and lifeless with blunted transients and a lack of bloom and fade, similar to when you have too much damping fluid in a tonearm. It turns out it was the power cord, a 12-yr-old Synergistic Research AC Master Coupler. Playing a hunch, I swapped out the SR AC MC for a late model PS Audio XStream Prelude, and voila! All the tubelike nuance, low level detail, instrument resonance and room ambience returned to the musical presentation. I got a second boost in transparency when I bypassed a filtering power strip for a direct connection to the wall.

09-18-08: Audiofeil
Low powered tubed amplifiers are a better match for horns than class d amplifiers.

Onkyo, Pioneer, Sansui, and Kenwood notwithstanding.

That's my formed opinion based on experience.

Nobody said anything about Pioneer, Sansui, or Kenwood. Your lumping of the Onkyo--and the incredible job they did with the A-9x55 series--in with them is desultory and dismissive.

The question wasn't an invitation to audio snobbery, but rather an inquiry whether a higher powered class D amp is categorically a bad match. I cited a professional review into very high sensitivity horn-based speakers powered successfully by the Onkyo. The high switching noise typical of a class D amp would make for a bad match with a high efficiency horn, but Onkyo of all the class D amp designers has put together a couple of features to lower the noise floor--a large, powerful analog power supply, and a patented circuit to mirror the switching noise and thus cancel it. Robert Deutsch's review verifies that it works. He also tried a $1500 Flying Mole class D and reported that it was unacceptable, and nowhere near as good sounding as the Onkyo.

That one might ultimately still prefer SETs is a separate issue.

It seems the old VTL Tiny Triodes would be a good matchup for such a speaker as well.

09-19-08: Audiofeil
Let's not confuse snobbery with years of experience.

Of which I suggest you seem to lack.

Good luck with your Onkyo or Pioneer or Kenwood or whatever.

Thank you. I rest my case.