On Class D Amplifiers Measurements

[restorer-john]

Hope your partner will recover soon!

My girl has been enjoying a minimum of three cooked meals a day, carefully selected for variety, taste and nutrition all prepared by her "personal chef" (me). P doesn't want to go back to work, ever.

Actually, I've enjoyed it as the kitchen is all mine (yeah), I don't find odd things in the fridge decomposing and chit is exactly where I left it. That said, sometimes you just want a takeaway pizza...

What I have come to understand is carers/partners put their life on hold. I never knew that. P is head of special education and deals with it all the time, everyday. The parents with multiple special needs kids etc. And her 'disability' is just temporary too!

I haven't listened to music for 2+ months, except for a few minutes on headphones. You feed others first, and yourself second. The garden gets totally overgrown. The cars need washing and vacuuming. The clothes chute to the laundry gets piled up and that's not because I didn't do the washing before, it's because doing the washing takes a backseat.

My parents are old. One or other, or both will need me soon enough. This has been good practice and I am thankful for that.

 

[BDWoody]

What I have come to understand is carers/partners put their life on hold. I never knew that. P is head of special education and deals with it all the time, everyday.

That's not a job for everyone... She sounds like a special lady.
Good for you for being able to have that perspective. That's the stuff that matters.
Speedy recovery to your girl.

 

[restorer-john]

Speedy recovery to your girl.

Thanks. Rare for me to inject personal chit into an ASR thread and I apologize, but hey, it's been a crazy past year. Her relatively minimal physical suffering and my inconvenience is nothing compared to the real soldiers out there.

406,000 good Americans lost to this thing. We hurt for you guys in Australia.

 

[BDWoody]

Rare for me to inject personal chit into an ASR thread and I apologize, but hey, it's been a crazy past year.

Indeed it has, and you can take the apology back...

 

[tmtomh]

If you did "fully get it", you wouldn't have gone off on a tangent about inaudible harmonics at 60kHz. There are none in that result. Shall we exclude all the harmonics of 5KHz at circa 0.1% too?

You accused me of spreading a myth about HF THD in Class Ds. I've just shown you an example, reviewed today, on ASR by our host. Clearly not a myth in this case is it?



Nobody was. If you took the time to read my post, you would see I was being very specific about the amplifier in question and included the link. I made zero representations as to the results applying to all Class Ds and unlike you, I do NOT make a habit of editing my posts after the event either.

Did you actually read this?
View attachment 107508

This particular thread is also a general Class D discussion about measurements. It is not an exclusive Hypex and Purifi thread. HF distortion was being discussed, my post, comments and link was, and is highly appropriate.

So please, put me back on ignore like you said you had. Then you won't feel the desperate need to come and attack everything I may write. It's so tiresome.

Are you saying all Class D amps exhibit the poor level of performance you are discussing here? If not, could you please give an example of one that does not exhibit this performance problem? Perhaps one whose performance is charted right on this very page of this thread?

 

[Blumlein 88]

Basically, I am saying that for every review that technically castigates typical Class D implementations, the quality performing products get dragged along for the ride.

As I said, it's not fair, but until the excellent performers outweigh the vast majority, the overall reputation will not improve. Instead of attacking the messengers of truth, proponents should be encouraging other players in the field to lift their collective game, improve their offerings and be honest for everyone's benefit.

That is what happened post 1974 thanks to our friends at the FTC. The current atmosphere is ripe for change and improvement.

So specifically what would you want the changes to be?

 

[DonH56]

Hope your gal recovers quickly and well, @restorer-john It's been a rough few years around here and lately this is not the place to come to relax.

On-topic: The usual issue with high-frequency distortion is not harmonic spurs, it is the intermodulation components that fall back in-band where they are audible.

 

[pma]

Definitely, and that’s why real experts like Bob Cordell were proponents of the THD30kHz test. Though it covers inaudible frequencies, it reveals nonlinearities and thus effect on intermodulations as well. Sadly, the 1kHz test is most appreciated here. A lot of learning would be needed.

 

[BDWoody]

Another misrepresentation

As has been discussed, the tone taken consistently when it comes to disagreements with others on the forum is just unacceptable, particularly from a manufacturer (privileged guest) when responding to a long time, highly respected member.
Also as has been discussed, you will receive a break from the forum as a result of not being able to follow these guidelines. One last try if/when you come back.

 

[MrPeabody]

Definitely, and that’s why real experts like Bob Cordell were proponents of the THD30kHz test. Though it covers inaudible frequencies, it reveals nonlinearities and thus effect on intermodulations as well. Sadly, the 1kHz test is most appreciated here. A lot of learning would be needed.

It shouldn't be terribly difficult to demonstrate this by performing tests for IMD using 30 kHz as the higher frequency.

 

[restorer-john]

So specifically what would you want the changes to be?

Wow, I could write a book on that.

Maybe a subject for another thread?

 

[Blumlein 88]

Wow, I could write a book on that.

Maybe a subject for another thread?

That sounds like a fine idea. I've read your posts in this and a couple other threads. It would be nice to have you start with a clean slate, lay out what you think is needed. And then maybe some discussion on why depending upon what you include (or leave out).

 

[restorer-john]

It shouldn't be terribly difficult to demonstrate this by performing tests for IMD using 30 kHz as the higher frequency.

We can do that with Class A/ABs, but it's not fair to Class Ds (in general).

As with many tests, we can pick stimulii or signals that will make one amplifier topology look good and another look bad.

 

[restorer-john]

That sounds like a fine idea. I've read your posts in this and a couple other threads. It would be nice to have you start with a clean slate, lay out what you think is needed. And then maybe some discussion on why depending upon what you include (or leave out).

I'd definitely need help and input. I'll give it some thought today on how best to present such a thread, so it doesn't end up a giant pile-on.

 

[SIY]

We can do that with Class A/ABs, but it's not fair to Class Ds (in general).

As with many tests, we can pick stimulii or signals that will make one amplifier topology look good and another look bad.

Could you maybe limit this to signals and demands that can actually be encountered? That was one of my beefs with the way FTC structured things- it measured how well the amp functioned as a continuous heater, not something whose function is driving a complex load with signals of constantly changing dynamics and frequency spectra.

You know my affection for and lust after the PowerCube.

 

[Matias]

I'd definitely need help and input. I'll give it some thought today on how best to present such a thread, so it doesn't end up a giant pile-on.

Suggestion? Start with the end customer in mind. He/she listens to music. Low or loud volume, calm or noisy music content (and it's power distribution in frequency), easy or difficult loads of speakers. In a living room or office, used for minutes up to all day long. You know, mainstream and power users included in these overall conditions.

Now how would a test best capture this real world use, and how would it rate different topologies and designs "blindly" to that "end user oriented" goal?

My main point here is to avoid the pitfall of today's unrealistic, lab benchmark test, which is easy for a technician to run but detached from real world usage.

Should be a fun exercise. Will like to read your thoughts on this.

 

[MrPeabody]

We can do that with Class A/ABs, but it's not fair to Class Ds (in general).

As with many tests, we can pick stimulii or signals that will make one amplifier topology look good and another look bad.

Okay, but (1) only suggesting that it should be possible to verify that harmonic distortion for fundamental frequencies above 20 kHz promotes IMD below 20 kHz, i.e., wasn't suggesting anything about pros/cons of one class vs. another, and (2) why would this kind of test be unfair to class D?

Class D has spectral content above 20 kHz that class A/AB doesn't have. But my sense is that it is so high in frequency that maybe it wouldn't promote IMD below 20 kHz. I can't think it through. And of course that high frequency content is mostly eliminated out using a steep low-pass filter. So I'm drawing a blank on this. And if class D is disadvantaged in this respect, isn't it a rub for class D generally, or are different class D amplifiers different in this respect?

 

[DonH56]

Wow, I could write a book on that.

Maybe a subject for another thread?

Count me in. Alan definitely has some good thoughts about it as well, though I am torn between making it more realistic and wanting to tighten some things up, or at least have a solid common standard for things like multichannel performance (I have half a dozen AVRs around the house; compared to 2-ch output, some make 90%, one makes 30%, with all channels driven).

 

[pma]

I think it is a good discussion here in we may continue in suggestions on intermodulation test signals and methods. How about a triple tone, any suggestions?

 

[boXem]

Instead of inventing new tests, why not using the 32 tones already used with DACs? Even if not very useful for a designer, it shows strengths and weaknesses at a glance. That's personally the only one I am looking at in reviews.