Anyone got objective tests on class D versus AB ?? Compare amplifiers with REW

[diablo]

I have been reading the "Audiophiles, generally don't like class D amps!" thread with some interest. There are many subjective statements but little evidence. I don't trust my own ears so unlikely to trust anyone else's.

I've been pondering getting a class D amp for many years but usually buy a trusted AB design instead. Though I did get an Aiyima A07 a while back. I ran a REW test on an AB amp then substituted the A07, leaving the speakers and Umik-1 in place. There was very little difference. I have subsequently replaced the Yamaha R-N803 I was using in my lounge with an SMSL A300. And it seems to be doing a good job.

However, I hadn't tested the A300 at all, so decided to a couple of days ago. I actually tested it against three other amps.
Yamaha R-N803D in pure direct mode
Yamaha RX-AS710D (oldish slimline Avantage AVR) in pure direct mode
Aiyima A07
I ran sweeps at three different levels on each, matching the levels as best I could. There was very little difference in what the microphone picked up. Here are the results for one channel at high-ish volume, separated to make spotting the differences easier -

The scale is magnified and not smoothed too much. There are minor differences. You may notice that the R-N803 and A300 look very similar. The AS710 and A07 are also similar to each other.

LH 803 710 A300 A07.mdat

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I will post another test I did to see if I could spot where the differences came from, which I will post shortly.
Anyone done a similar exercise?

 

[BR52]

I like your overall test, et least it shows how different amps handle your specific speakers, damping over full frequency range .......

 

[DVDdoug]

Every amp is going to measure differently so it's hard to generalize and it's possible to make a class-A, A/B, or D amp that's better than human hearing.

The same goes for tubes, transistors, MOSFETs, and integrated circuits. There are things about vacuum tubes that make it difficult and expensive, especially power amplifiers because tubes need an output transformer. And I don't think it's practical or economical to make a class-D amp without ICs.

It seems like everything is heading toward Class-D and that makes sense because there are lots of advantages. The main disadvantage is that the circuitry is complicated but a lot of circuitry can be crammed-into an inexpensive chip.


P.S.
You don't normally measure an amp with microphone... Normally you measure it electrically without the effects of speakers, room acoustics, or a microphone. All of these things degrade the sound worse than an amplifier (assuming the amp isn't broken). Sometimes you might want to measure it with an actual speaker load and/or with different speakers to see if the load affects the output, but you still measure the output electrically.

 

[diablo]

Following on from my previous test, which showed minor differences, I tried a similar test using an LS50 Meta with the A07 and 803. Connected to the PC by a Topping D10S.

This time the small differences were absent. So I'm assuming that it is maybe differences in the crossover of the XTZ 99.36 FLR speakers I used for the first test?

With the A07 you can see the FR rise above 2K by roughly half a decibel.

A07 803 on LS50.mdat

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[diablo]

P.S.
You don't normally measure an amp with microphone... Normally you measure it electrically without the effects of speakers, room acoustics, or a microphone. All of these things degrade the sound worse than an amplifier (assuming the amp isn't broken). Sometimes you might want to measure it with an actual speaker load and/or with different speakers to see if the load affects the output, but you still measure the output electrically.

Yes, I'm aware of that. But since I first considered a class D amp, probably around 2010, I've seen cases where the amps measure well when connected to a dummy load, but poorly in the real world. After all I want to use them with speakers.

I think they've mainly got that sorted nowadays.

 

[Tom C]

Have you tried, as a control, measuring the same amp two or more times, to see if the results are consistent? It’s possible that other factors, aside from changing amps, are influencing the result. Just taking the same amp out and putting it back in could maybe give a slight variance in the measurement.

 

[MaxwellsEq]

This is interesting. However, you need to be aware you are measuring your room, acoustic background noise, and your body if you are in the room. If the cases of the amplifiers are different or located slightly different, you will also potentially get different results.

 

[diablo]

Have you tried, as a control, measuring the same amp two or more times, to see if the results are consistent? It’s possible that other factors, aside from changing amps, are influencing the result. Just taking the same amp out and putting it back in could maybe give a slight variance in the measurement.

I wondered that too. So I sometimes ran tests several times, in case road noise (or my central heating) was altering the results. I tried to keep everything identical, doors closed, all equipment in the same place (just changed connections) and where I was sat.
On the second test I added a 15 foot cable to one of the R-N803 tests to see if it was the high damping factor whch made the difference - but no change.

 

[Tom C]

As long as the results are consistent when measuring the same amp two or more times, any differences detected should be attributable to the differences in amplifiers.

 

[diablo]

A few weeks ago, on another thread, I posted a picture of insides of my three Aiyima A07amplifiers, showing that they all had different capacitors - they were bought at different times. So I thought I'd run the test described above to see if the changes had altered the frequency response. All three amps were set to max volume. The three graphs overlapped each other. They were identical. I expected some differences in such low cost amps.

I assumed that someone else had thought of this idea on testing previously, so I googled "compare amplifiers using REW" and only one really similar result appeared, on ASR of course.

run REW on different amps that measure similiar

I know it is an ongoing argument that 'testing doesn't reveal everything about an amp' but I'm curious if anyone has ever run REW on several different amps that measure very similar. I've done it with quite different amps and got results that overlapped in some areas and in other areas were...

www.audiosciencereview.com

If you look past the doubting posts you will see that member Pavel (pma) ran some good tests on a couple of amplifiers.

The testing has had a result for me. I was wondering if getting a Purifi or Hypex based amp for my lounge was worthwhile. As I have no need for the extra power I can't justify it.

 

[pma]

A07 a while back. I ran a REW test on an AB amp then substituted the A07, leaving the speakers and Umik-1 in place. There was very little difference. I have subsequently replaced the Yamaha R-N803 I was using in my lounge with an SMSL A300. And it seems to be doing a good job.

A07 and all class D amplifiers based on the same topology have huge dependence of FR on speaker impedance at high frequencies and it is easily audible in a DBT test. I posted myriad of posts on this. Let me be lazy and mention just one thread, the rest can be found by search engine here.

Class D A07 x class D UcD180 and class AB amp - there are measurable differences on acoustical side

I’m still not getting how this is a class AB vs class D thing then. It might be an issue with the A07’s power supply, or even with the PC or interface, but the amp itself works perfectly well it seems.

www.audiosciencereview.com

 

[diablo]

A07 and all class D amplifiers based on the same topology have huge dependence of FR on speaker impedance at high frequencies and it is easily audible in a DBT test. I posted myriad of posts on this. Let me be lazy and mention just one thread, the rest can be found by search engine here.

Class D A07 x class D UcD180 and class AB amp - there are measurable differences on acoustical side

I’m still not getting how this is a class AB vs class D thing then. It might be an issue with the A07’s power supply, or even with the PC or interface, but the amp itself works perfectly well it seems.

www.audiosciencereview.com

Thanks for that. I've had a glance at some of your threads and will look more closely later.
I noticed the difference in treble response with my test on the LS50. I seem to remember much bigger differences with various speakers with older designs, which was one of my concerns.
The A300 which has replaced my Yamaha in the lounge has identical response at three different volume levels, so I'm happy with that.
Everything goes through my MiniDSP Flex anyway, so any changes are smoothed out by Dirac.

 

[JRS]

As long as the results are consistent when measuring the same amp two or more times, any differences detected should be attributable to the differences in amplifiers.

Most importantly, it is objective evidence. No I'll defined and often ephemeral (curiously invariably revised opinions within a review are improvements vs on second thought after having listened for two weeks they have intolerably brittle tone unmitigated by rather wooly bass.

 

[valerianf]

@diablo , did you notices any hiss at the tweeter level?
It is a commun problem with class D amps.

 

[diablo]

@diablo , did you notices any hiss at the tweeter level?
It is a commun problem with class D amps.

I have tried turning the volume up and listening close to the tweeters but heard nothing. The only speakers I've tried the class D amps with are max 85dB efficient, and I think hiss is more common with higher efficiency speakers.

Plus I'm rather old, so my hearing range doesn't go much above 9kHz these days so there might have been hiss there which I couldn't detect. So not got a definite answer.

 

[Eliseo Moran]

Every amp is going to measure differently so it's hard to generalize and it's possible to make a class-A, A/B, or D amp that's better than human hearing.

The same goes for tubes, transistors, MOSFETs, and integrated circuits. There are things about vacuum tubes that make it difficult and expensive, especially power amplifiers because tubes need an output transformer. And I don't think it's practical or economical to make a class-D amp without ICs.

It seems like everything is heading toward Class-D and that makes sense because there are lots of advantages. The main disadvantage is that the circuitry is complicated but a lot of circuitry can be crammed-into an inexpensive chip.


P.S.
You don't normally measure an amp with microphone... Normally you measure it electrically without the effects of speakers, room acoustics, or a microphone. All of these things degrade the sound worse than an amplifier (assuming the amp isn't broken). Sometimes you might want to measure it with an actual speaker load and/or with different speakers to see if the load affects the output, but you still measure the output electrically.

I agree with that comment abot using mics and speakers for testing: better use an spectrum analyzer to this kind of comparisons. It is easy to compare THD specs for amplifiers (considering the complete frequency range and different power levels). Considering the latest Texas Instrumens class D ICs, I do not think anybody can perceive distrortion level for a well designed and constructed class D amp. For me, the main problem with class D, as with class AB, could be the lack of current peak capabilities with low sensitivity and/or high demanding speakers. For the price of an A07 you can test the system for little amount of money. If it convinces your ears it is OK for you. If you want to compare systems seriosly, it is a completely different issue.