Class D and High Efficiency Speakers?

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.

There is really no inherent sonic advantage to Class D, aside from the ability to deliver a LOT of power, and a whole lot of potential problems, most if not all that can be handled by proper implementation. But, if one does not need a whole lot of power, why go Class D?

I got to hear a $14,000 Rowland Class D amp on my friends 106 db/w efficient speaker system. The sound was quite unsatisfactory -- no top end air, oddly sterile and bland sound, lacking in full harmonic structure -- this in comparison to some very good pushpull tube amps (45s). Tubes, generally speaking, sound terrific at low power outputs and have problems with higher power; transistors seem to be just the opposite.

There are a lot of very good speakers that need a bit of power; a Class D amp would be more suited for that application.

I am running a pair of NuForce 9 SE V2 to drive my Coincident Eclipse 111. The speakers have an efficiency of 94 db. The sound is spectacular. I chose the NuForce amps for the quality price ratio.

I would suggest taking up NuForce on their offer of a free (or almost free) trial of the amps to hear them in your own system. FYI, they are really not a class D amp. See the web site for further explanation.

High Efficiency speakers in general prefer an amplifier with a relatively high source impedance, due to the reactive nature of high efficiency drivers.

The use of low output impedance amplifiers with high efficiency drivers is the reason why horns have a reputation for being strident.

If you really are intent on this, add an 8-ohm resistor in series with the speaker load. True, you will dissipate likely up to 50% of your power in the resistor, but it will simulate (somewhat) a higher source impedance.

Or- you could get a tube amp. You won't need a lot of power. In the case of a high efficiency speaker, a good tube amp will clean the clock of any class D amplifier made.

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.

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.

Thanks for the replies guys. I already have 300B mono blocs, I'm just interested if anyone has implemented a class D amp with high efficiency.

Anyone tried the Bel Canto Ref1000, with high efficiecny?

I use the Tripath based Red Wine Audio 30.2 on my Cain Abbys, 95 db. I'm a 300b lover and have several SET amps. In the summer it's tough to keep things cool with all the tubes and this has been great. It has more of the cushioned sound I hear in tubes than some of the other digital amps I've tried. Good luck.

I design speakers specifically intended to work well on low damping factor tube amps, but double-check them on a high damping factor solid state amp (one that has been mentioned in this thread) to make sure I'm not painting myself into a corner.

In my opinion, even when the speaker works well with both types, the low damping factor tube amp sounds better.

Now, if your high-efficiency speakers were designed to be driven by solid state (constant-voltage) amplification, they may sound better with a Class D amp than with your 300Bs.

Duke
dealer/manufacturer

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.

Thanks for the input guys. It seems that If I really want to satisfy my curiosity I am just going to have to give them a go with my speakers.

Cheers

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.

I tried, keep going with tubes. But since I manufacturer loudspeakers I have to keep class d about to test on loudspeakers. Why not a class a ss amp? I find these better than Class D.

Johnk,
Understood.

As a retailer I have various class d amps here which I switch in and out of systems to understand the strengths and weaknesses.

They are a godsend for difficult loads when space, heat, and budget constraints exist.

And the sonic quality is becoming very very good with the proper load.

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.

Johnnyb53, trust me, Audiofool, will not give it a rest. He knows all. Good luck.

The subject of class D always seems to bring on the detractor who's class D experience can be limited to varying degrees. My red flags pop up when I hear the general reference to class D and not a specific model.

While I still own a fine tube and linear solid state amplifiers I'm terribly class D biased. Class D amplifiers are far more sensitive to their physical and electrical environment than most other designs. In many cases AC line conditioning can simply make things worse. Class D is not plug and play.

Warnsy! Your own advise is the best so far, try it yourself. I did hear a system with some home made horn enclosures powered by an early version of Red Wine amplifiers and the music was stunning. I haven't followed Red Wine's progress but I'm sure they've been busy improving their design.

My personal switching amplifier advances have come from: a dedicated shielded AC Circuit, mass loading the casework, replacing a tubed preamplifier with a battery powered solid state preamp.

Of the eight class D amplifier I've had in my system and either before or after my systems upgrades I have never experienced what someone referred to as 'switching noise' from the amplifier. As I understand it the switching occurs at 50kHz and usually much higher.