Class A/AB vs D -- Is it Audible in 2021?

[Roland68]

I recently replaced a 25 years old onkyo integra stereo amp with a fosi BT20A pro.
At low volume the difference I can detect is a faint hum with the old onkyo. But it's so low that I can only hear it with my ear near the tweeters.
But at high volume the old onkyo sounds better. I would describe the sound as less compressed and with better bass control.
The fosi outputs 2x40W @8ohm (36V powerbrick). The onkyo is rated at 2x80W @8ohm, but one channel is dead so I only used 1 channel.
So I assume the rms power is fairly equal.
Someone in my neighborhood had a 15 year old hk amp for sale. It was cheap and in fine condition. So I bought it and use it to power my subwoofer.
Relieved from the sub duties the fosi sings a lot better with mid and high frequencies.
So I have been wondering why the 1x80 from the old onkyo seemed more powerful than the 2x40 (with identical loads). And dynamic headroom seems the only logical explanation.
I know it could all happen in my head. But after amirms test I had high expectations for the fosi amp and really wanted to love it. And together with the HK amp I actually do like it a lot.

Maybe I'm missing some other explanation as to why the fosi seemed lackluster compared to the old onkyo?

The Fosi will also sound lackluster against a PA5. This is due to the simpler structure of the Fosi. The simple power pack does the rest.
How did you connect your speakers to one channel of the Onkyo?

 

[antcollinet]

I recently replaced a 25 years old onkyo integra stereo amp with a fosi BT20A pro.
At low volume the difference I can detect is a faint hum with the old onkyo. But it's so low that I can only hear it with my ear near the tweeters.
But at high volume the old onkyo sounds better. I would describe the sound as less compressed and with better bass control.
The fosi outputs 2x40W @8ohm (36V powerbrick). The onkyo is rated at 2x80W @8ohm, but one channel is dead so I only used 1 channel.
So I assume the rms power is fairly equal.
Someone in my neighborhood had a 15 year old hk amp for sale. It was cheap and in fine condition. So I bought it and use it to power my subwoofer.
Relieved from the sub duties the fosi sings a lot better with mid and high frequencies.
So I have been wondering why the 1x80 from the old onkyo seemed more powerful than the 2x40 (with identical loads). And dynamic headroom seems the only logical explanation.
I know it could all happen in my head. But after amirms test I had high expectations for the fosi amp and really wanted to love it. And together with the HK amp I actually do like it a lot.

Maybe I'm missing some other explanation as to why the fosi seemed lackluster compared to the old onkyo?

Even if we ignore the fact that you are not testing blind so we have no idea if you would really be hearing a difference, if the test had any validity at all.

But... there are so many huge differences - level matching... non existent, one of the amps is a bottom dollar cheap design of a type that always overstates it's power output.... compared with an established brand from the era of amps being designed and built to a different and more honest standard....and.... I don't know what else. BUT - in one case you are only getting music from one speaker.

What on earth makes you think that isn't the reason for it sounding better? But no - it must be because one of the amps is class AB and the other is D.

Yes, you are missing a myriad of other explanations.

 

[WinWiz]

You mean more like 120 watts of short term pulse power.
With its top amplifiers, HK often specified a 50% higher pulse power at 4 ohms (80W -> 120W), but this was not achieved in the various laboratory tests either.
1200W pulse power (at nominal 80-100W) belong in the fable area of the audio world and were used by dubious companies for marketing. I haven't seen such dishonest statements from HK in the last 40 years.

Manual say

Even if we ignore the fact that you are not testing blind so we have no idea if you would really be hearing a difference, if the test had any validity at all.

But... there are so many huge differences - level matching... non existent, one of the amps is a bottom dollar cheap design of a type that always overstates it's power output.... compared with an established brand from the era of amps being designed and built to a different and more honest standard....and.... I don't know what else. BUT - in one case you are only getting music from one speaker.

What on earth makes you think that isn't the reason for it sounding better? But no - it must be because one of the amps is class AB and the other is D.

Yes, you are missing a myriad of other explanations.

The 2x40w is not marketing -its from ASR test.
In both cases I was running 4 8ohm speakers connected in serial+parallel connection so effectively a 8ohm load.
Edit: Actually my tiny fullrangers are nominal 4ohm speakers. So with the onkyo it was effectively 1x4ohm load. With the fosi I connected each pair in serial, so a 2x8ohm load.
I used a dsp to sum left and right channel.
But you are correct no level matching I just replaced the old onkyo and played a few tracks at different volumes expecting an upgrade but noticed a downgrade...

I'm not saying class AB is superior. I'm just saying two 80w amps might not be equal if one is voltage limeted while the other amp isn't.
Looking at the fosi's drop in output from 2x70w@4ohm to 2x40w@8ohm I imagine output is pretty low when my speakers impedence reach 28ohm around 70-80hz.
So maybe my preferred volume cause the fosi to clip when playing bass. Or maybe the onkyo also clips but sounds better when driven into clipping? I don't know, but would like to know....

 

[WinWiz]

The Fosi will also sound lackluster against a PA5. This is due to the simpler structure of the Fosi. The simple power pack does the rest.
How did you connect your speakers to one channel of the Onkyo?

With my ears, speakers and listening environment I would not expect to detect any difference replacing a 83 sinad amp to something above 100. If they had similar power...

 

[Roland68]

Manual say
The 2x40w is not marketing -its from ASR test.
In both cases I was running 4 8ohm speakers connected in serial+parallel connection so effectively a 8ohm load.
Edit: Actually my tiny fullrangers are nominal 4ohm speakers. So with the onkyo it was effectively 1x4ohm load. With the fosi I connected each pair in serial, so a 2x8ohm load.
I used a dsp to sum left and right channel.
But you are correct no level matching I just replaced the old onkyo and played a few tracks at different volumes expecting an upgrade but noticed a downgrade...

I'm not saying class AB is superior. I'm just saying two 80w amps might not be equal if one is voltage limeted while the other amp isn't.
Looking at the fosi's drop in output from 2x70w@4ohm to 2x40w@8ohm I imagine output is pretty low when my speakers impedence reach 28ohm around 70-80hz.
So maybe my preferred volume cause the fosi to clip when playing bass. Or maybe the onkyo also clips but sounds better when driven into clipping? I don't know, but would like to know....

Exactly what I thought.
You operated the Onkyo with 4 ohms, i.e. around 140-150W nominal and around 200W pulse power against the Fosi with 2 x 40W at 8 ohms and a very small power supply.