Advance in Class D amps?

[Zaphod Beeblebrox]

Zaphod ... if you were to design an active subwoofer, with your choice of driver impedance characteristics would you choose Class-D for the amp duties or would you still prefer Class-AB?

I would expect that Class D should be the way to go. However, given my preference for a specific type of Class A/B amplifier, I would also experiment with that as well. If I was restricted to high global NFB linear amplification, or Class D, then Class D would be the logical choice. If the choice was expanded to include zero global NFB amplification, then I will reserve judgement.

[georgehifi]

Here is a qote from Tim de Paravicini of EAR fame.

"There's nothing to stop me doing new technology, I'll use transistors.

If somebody wanted me to do class-D switching amplifiers and I thought they were good, I would do them. If I thought they were good."

http://www.allegrosound.com/EAR_869_3_AllegroSound.html

Cheers George

Edited April 3, 2012 by georgehifi

[Arg]

_{Tim de P has a long history of saying whatever lies he needs to back up his product line or just for the heck of it. Heaps of ability, heaps of knowledge, but just not trustworthy. Most unfortunate.}

[gainphile]

It's been said that Class D are not so good at the highs. I have been aware of this, running a paralled tweeters at 2 ohms nominal for my active 4-way dipoles. But to how much effect?

So today I measured the following, first I use chip amp (LM3875). They happily take the load no problems. But then as seen below my Sure ClassD loses -3db at 20hz (this does not happen with single 4 ohm tweeter)

The loss is first order lowpass, and very easily corrected with shelving highpass filter.

The correction gives back the airy sound.

It would be interesting if instant-switching of the amps were possible, but swapping them around I do not notice one being better than the other. Safe enough to say they sounded the same, and certainly nothing to draw attention to.

[Dismord]

I don't quite follow the problem with switching frequency. Having a look at the Hypex charts, and also at the Nuforce V3 technology, they both seem to be very linear and capable of high fidelity reproduction. Where do they lose out? The Nuforce is now employing an improved capacitor board which should help to smooth things out as well, surely?

I ran Nuforce V3 (MkII?) monoblocks and although I found them impressive I was always aware of running electronics. Sorry I can't explain that more clearly. A chance encounter in HK with Icon Audio MG 845 'Special' mono blocks bought back the goose bumps I'd been missing so I bought them even though valve amps scare the hell out of me every time I turn them on. Haven't regretted the move although I find I need to hand over everything below 45 Hz to a pair of subs.

[Zaphod Beeblebrox]

I ran Nuforce V3 (MkII?) monoblocks and although I found them impressive I was always aware of running electronics. Sorry I can't explain that more clearly. A chance encounter in HK with Icon Audio MG 845 'Special' mono blocks bought back the goose bumps I'd been missing so I bought them even though valve amps scare the hell out of me every time I turn them on. Haven't regretted the move although I find I need to hand over everything below 45 Hz to a pair of subs.

This may help with an explantion:

http://www.hardwareanalysis.com/content/article/1828/nuforce-reference-8-amplifier/

And the improved model:

http://www.hardwareanalysis.com/content/article/1831/nuforce-reference-9-02-amplifier/

Class D has quite a ways to go, before it reallly challenges the best linear amplification.

[georgehifi]

It all turns pretty nasty on both amps even on the 9.v2 from the upper mids right up to 20khz and beyond, compared to good linear amps, even at only 10watts.

The version 3 filters have better noise figures but kills even more of the upper harmonics structure with it's heavier filtering of the switching noise.

They have a long way to go. And there's no hope in the foreseeable future for higher switching frequencies yet for mass production use of class d to fix the problems, so far they are still good bass and mid fi amps.

Cheers George

[Zaphod Beeblebrox]

It all turns pretty nasty on both amps even on the 9.v2 from the upper mids right up to 20khz and beyond, compared to good linear amps, even at only 10watts.

The version 3 filters have better noise figures but kills even more of the upper harmonics structure with it's heavier filtering of the switching noise.

They have a long way to go. And there's no hope in the foreseeable future for higher switching frequencies yet for mass production use of class d to fix the problems, so far they are still good bass and mid fi amps.

Cheers George

I'm more than a little concerned with the high levels of distortion at low levels.

[richard260]

This may help with an explantion:

http://www.hardwarea...ce-8-amplifier/

And the improved model:

http://www.hardwarea...9-02-amplifier/

Class D has quite a ways to go, before it reallly challenges the best linear amplification.

Wow i always thought nufore amps were good.These look very average.And how much do they charge for these amps

[RockandorRoll]

Acquired taste?

All i know is my KT88's are collecting dust while the Bel Canto gear takes centre stage. I dont feel like im ever missing anything.

[DoggieHowser]

I recently swapped my Bel Canto REF1000Ms with a pair of Electrocompaniet AW600 Nemos.

Power was supplied using ASI power cords through a Sound Application RLS240 conditioner. Preamp was an Audio Research Reference 5SE.

The Bel Cantos sounded a tad lean with the Bel Canto Pre3 and partnered with my Thiel CS3.7s. But with the new conditioner and cords plus tube preamp, the sound was noticeably fuller.

Since I switched to the Nemos, I can't say I've noticed a big improvement in the midrange or highs compared to my previous setup. But the bass does seem to have more authority and more meat to it.

Considering how much the Nemos were, I'd say the Bel Cantos were a bargain.

[sir sanders zingmore]

I heard a stack of nemos driving the B&W Nautilis at Tivoli Hifi. Was very disappointing.

Edited April 6, 2012 by Whatmore

[gainphile]

It all turns pretty nasty on both amps even on the 9.v2 from the upper mids right up to 20khz and beyond, compared to good linear amps, even at only 10watts.

Cheers George

Interesting.

I will check tonight at the speaker output. My understanding is transducer distortions much outweigh these electronics.

[A J]

Acquired taste?

All i know is my KT88's are collecting dust while the Bel Canto gear takes centre stage. I dont feel like im ever missing anything.

That's because you have the best sounding Bel Canto around I loved it - never lean - awesome power and solid bottom end.

[Zaphod Beeblebrox]

Interesting.

I will check tonight at the speaker output. My understanding is transducer distortions much outweigh these electronics.

Some ESLs and other speakers exhibit lower distortion than most Class D amps.

[DoggieHowser]

Odd. The Nemos have been very highly rated with Nautilus. Have you heard the Nautilus with other amp combinations?

I've heard it with Thiels in the showroom and have found the partnership great as well.

Edited April 6, 2012 by DoggieHowser

[Arg]

.... My understanding is transducer distortions much outweigh these electronics.

Completely correct. Even for electrostatics.

I can't figure from reading this thread whether discussion is about the worst class D or the best.

The OP pointed a link to one of the best. Distortion from the best electrostatic speakers would be about 100x that of the ncore class D amps. It's a non-issue.

High end class D is hobbled not by what it can do, but by what it's ancestors couldn't do.

[Art Vandelay]

Completely correct. Even for electrostatics.

Distortion from the best electrostatic speakers would be about 100x that of the ncore class D amps. It's a non-issue.

High end class D is hobbled not by what it can do, but by what it's ancestors couldn't do.

The main problem is the high order nature of class D distortion. THD may well be lower but the harmonic profile is more audible.

Another potential problem is the amount of RFI generated by many class D amps. The RF energy can lead to degraded performance of source equipment and preamps etc that may not be adequately designed to cope with the high level of RF being generated within close proximity.

Sure they're getting better, and the best class D amps do sound pretty good but the only advantages they will ever have over class A, AB, or B solid state legacy designs is higher efficiency and smaller size.

FTR, many dynamic speakers now achieve better than 0.2% THD at mid and high frequencies.

[Zaphod Beeblebrox]

Completely correct. Even for electrostatics.

Not so much.

http://www.quad-hifi...En&Tab=ESL-2805

http://www.quad-hifi...En&Tab=ESL-2805

And:

http://www.quad-hifi...En&Tab=ESL-2905

Above 10kHz, both Quads are lower distortion than the Nuforce 8.

http://www.duntech.c...images/all.html

The Duntech Sovereign is rated at less than 0.3% THD above 80Hz. This figure is comfortably better than the Nuforce 8 above 15kHz. Either way, distortion is so low, that it is likely to allow an amplifier that exhibits as much distortion as the Nuforce 8 and 9 does, to intrude. Good engineering practice demands that the amplifier should deliver AT LEAST 10 times less distortion than the speaker system.

I can't figure from reading this thread whether discussion is about the worst class D or the best.

The OP pointed a link to one of the best. Distortion from the best electrostatic speakers would be about 100x that of the ncore class D amps. It's a non-issue.

Really?

High end class D is hobbled not by what it can do, but by what it's ancestors couldn't do.

Until the switching frequencies of Class D amps is raised considerably higher than it is today (5 ~ 10MHz should be adequate), then the best linear amplifiers have little to worry about. And, as Art has mentioned, it's not JUST about THD.

Edited April 6, 2012 by Zaphod Beeblebrox

[Drizt]

Zaph, where are the measurements to compare?

And distortion figures should always be counted over the entire audible range. Quoting figures above 80Hz etc is misleading IMHO.

Edited April 6, 2012 by Drizt

[gainphile]

I have taken the following data. I agree that THD number are meaningless.

These are taken from the loudspeakers (Tweeter, XT25 + Monacor Waveguide). Acoustic output is what matters right ?

The amps in question:

[gainphile]

First, ye olde distortion sweep.

Ignore those notches on the fundamental FR, as they are waveguide EQ which have not taken into effect at 2cm from XT25 Tweeter's cone.

2nd order distortion is very close, and similar in trends/profile. You could even argue Class D is marginally better.

Higher order distortions are equal.

Even at its worst points the 2nd order distortion is less than -45db.

Edited April 6, 2012 by gainphile

[gainphile]

Next, the Tone test.

Blue = gainclone

Black = ClassD

The 2nd order distortion is clearly visible at fundamental frequency * 2, and higher orders are barely visible.

In all cases the distortion matches exactly between ClassD and Class AB.

2khz:

5khz

10khz

20khz

Next, compiling data for intermodulation distortion using burst signals. It will take sometimes ...

Edited April 6, 2012 by gainphile

[rantan]

Sure they're getting better, and the best class D amps do sound pretty good but the only advantages they will ever have over class A, AB, or B solid state legacy designs is higher efficiency and smaller size.

An excellent point and one which exposes Class D for the over-hyped technology that it is.

[Arg]

"Over hyped"???

All the 'hype' on this thread is decidedly dismissive!