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Class D Switching Power Amplifiers and Power D/A conversion

CLASS AB Amplifier Vs CLASS D Amplifier
CLASS AB Amplifier Vs CLASS D Amplifier
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Old 28th August 2011, 03:53 AM   #11
kenpeter is offline kenpeter  United States
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I test class D all day, measures fine w sines.
Horrible to listen to with real music. The way
it clips into real speakers with music of any
level, awful... Sorry engineers, compression
over the long time constant doesn't "fix" the
problem.

Can't wait to get home and listen to my tubes.
Yet, I don't think Class-D is beyond all salvage.
Try to tell a chip engineer to preemptively soft
clip before hard voltage and current limits is a
tough sell. That sort of processing is someone
else's job. I've had no luck presenting my ideas.

And that it behaves as a negative resistance
to the power supply, got those cutting in and
out too. No idea how to fix that aside from
setting stOOpidly high safety limits at the PS.
Maybe its just my Agilents? Overpriced crap...

Last edited by kenpeter; 28th August 2011 at 04:11 AM.
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Old 28th August 2011, 03:56 AM   #12
nkdecibels is offline nkdecibels
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Hi opc,

So the main application of this product would be any portable PA appliation as well as the Mobile DJ Applications.

So what is your conclusion, should i use Class AB or Class D amplifier module.

Regards,
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Old 28th August 2011, 04:12 AM   #13
NMOS is offline NMOS  Germany
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Quote:
Originally Posted by nkdecibels View Post
Hi opc,

So the main application of this product would be any portable PA appliation as well as the Mobile DJ Applications.

So what is your conclusion, should i use Class AB or Class D amplifier module.

Regards,
Class D for Subbass yes, but for soundquality in mid and high , no thanks only class AB or Class H
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Old 28th August 2011, 04:33 AM   #14
opc is offline opc  Canada
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CLASS AB Amplifier Vs CLASS D Amplifier
Hi kristleifur,

It might be more accurate to say that there have been some improvements that have helped to mitigate some of the disadvantages of class D amplifiers. Nothing groundbreaking has happened in the past 5 years in terms of class D amplifier design... marketing hype aside.

1. The LC filter at the output inherently limits your power bandwidth. There's no way around it. Post filter feedback can help a little at very low power levels, but not at higher power.

2-3. I would call those measurements acceptable, but not excellent. They've also done a fair amount of fudging to get there. They call it a 2x150W amp, but they've intentionally measured it under conditions that make it a 75W amp. Using lower voltage rails helps to lower the noise and also lowers distortion. They do state this, which is good, but these are not measurements from a high power class D amp. Also, that 0.008% is only at 10W and only below 1kHz. Above that, things degrade quickly.

Also note that a 2nd harmonic at -80dB is nothing to write home about. I've seen loudspeakers with distortion levels that low under the right conditions. There are also a lot of higher order harmonics in there. The 16th harmonic is clearly visible and that's with limited measurement BW.

If you want to see good measurements, check out the datasheet for the LME49830. I mocked up a little class AB amp last year with that IC and a pair of lateral FETS with 0.5A of bias current and 50V rails. It measured a factor of 10 better than what you linked to in every respect.

4. Of course it matters! Why would you invest in an amp that peaks by 2dB at 15kHz when a class AB doesn't? There are also phase issues involved that you don't get with a class AB. Nobody has actually solved this issue yet, and I have never seen a response graph with 2, 4, 6, 8, and 16 ohm responses that are all perfectly flat to 20kHz. Even a poor class AB can manage that.

5. You are correct that for some of the modular all in one IC's there is significant space saving (and none of the complexity) but for two comparable discrete designs, the class D amplifier will be significantly more complex to build and work with.

6. "If the design is done properly" - That's a big "if"! All switch mode amplifiers and supplies suffer from EMI/EMC issues, and it can be extremely difficult to deal with them! The integrated IC solutions obviously pose less of a risk if they're implemented as specified in the datasheet, but even then it can be an issue.

Overall though, what's the point in dealing with all of the above if you have a perfectly viable solution in a class AB amplifier that has none of those problems? The only two legitimate reasons are power density and efficiency, and depending on the application those can be very good reasons.

As an audiophile though, there's no good reason to use a lesser performing amplifier just because it's a little more efficient and affords you a little more power per litre/kilogram. The whole point is to get the best sound regardless of those other criteria. It you want the best sound, then Class D is not where it's at.

Cheers,
Owen
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Old 28th August 2011, 04:39 AM   #15
opc is offline opc  Canada
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CLASS AB Amplifier Vs CLASS D Amplifier
Hi nkdecibels,

For mobile DJ/PA use, I'd say definitely go for class D throughout. In those conditions it's unlikely you'll notice a sound quality difference, and the weight savings alone make it well worth it. You actually do need high power for PA, and the best way to get there is class D in my opinion.

When it comes time to build something for your living room though, do yourself a favor and steer clear of the class D amps.

Cheers,
Owen
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Old 28th August 2011, 08:44 AM   #16
AP2 is offline AP2  Italy
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Hi,
After read this thread, i say...what type di D class you have listen?
Obvious that 80-100w A-B class is real good for HF driver but..some D class (serious develop) have not difference. i mean:linearity,thd,FR and response Vs. load. also 1,5dB from 4R to open load is very good.

Regards
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Old 28th August 2011, 12:12 PM   #17
The golden mean is offline The golden mean  Sweden
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Quote:
Originally Posted by Saturnus View Post
A categoric statement usually don't start with: "In my opinion..."
Indeed it can! The core of a categoric statment is the lack of the perception of uncertainty that we ought to account for if we want to be trusted.

A categoric statement could not be saved by "in my opinion" because if you maintain that your statement is by definition true it becomes obviously rather worthless to us as it proves noting. From Wikipedia;
" Tautology (logic), a technical notion in formal logic, universal unconditioned truth, always valid." Thus its hard to contradict such a statement.

A generalization like "all class D amps are better than all class AB amps has an intrinsic weakness; it demands to be more precise, in what respects? It is also hard to prove such a statement as neither you nor I have had the opportunity to compare all amps in the world.
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Last edited by The golden mean; 28th August 2011 at 12:19 PM.
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Old 28th August 2011, 12:51 PM   #18
kristleifur is offline kristleifur  Iceland
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None of the technicalities that opc mentions actually matter The sound quality does matter, and good Class D actually sounds great. There are numerous reviews around; I take issue with the portrayal of Class D as implausibly inferior sounding.

It's all good. I'm sure there are great Class-AB amps out there, I just haven't heard them yet.
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Old 28th August 2011, 05:34 PM   #19
kct is offline kct  Canada
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CLASS AB Amplifier Vs CLASS D Amplifier
When designed and build right, a Class D makes for a great power supply for a decent Class AB tho. Otherwise Class D has only very limited use in my books, may be ok to use with subs or servos and of course all battery driven devices. Other than that, Class D (and all the other ROHO's stuff for that matter) - No Thanks.

Until Class D signal reproducing issues are not resolved, I would not consider it fit for use. Not sue what some mfg's such as ADAM audio were aiming for when releasing there studio monitors equipped with this unfit Class D technology, it spoils the otherwise superb speaker.

But then it all depends, if quality is not so important and efficiency is requirement, then Class D has it's place, I guess.
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Old 28th August 2011, 06:24 PM   #20
Saturnus is offline Saturnus  Denmark
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To expand on what I said earlier. It's true that some class D amps aren't properly designed and therefore aren't terribly good but from person experience then a well built class D far exceeds the sound quality achievable by class AB or class A amps regardless of price.

So for a modern amp you so only consider class D if you care about sound quality at all, class AB is basically junk only suited for the scrapheap.
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