Class A vs AB -- Do They Really Sound Different?

[Vespa_SS180]

It was a very large and well-known company that did professional audio and consumer audio sort of like JBL but not JBL. I was an engineer at JBL also back in the day.

Like Altec Lansing perhaps ?

 

[MakeMineVinyl]

Like Altec Lansing perhaps ?

Could be.

 

[Vespa_SS180]

Could be.

I just yesterday watched reviews of model 19, a magnificent piece of audio gear. Hard Core.....

 

[pma]

@MakeMineVinyl , you can build absolutely perfect solid state class A of some 30W/8Ohm with distortion better than -130dB and negligible noise. No SE tube would compete neither in noise nor in distortion. And your horn issue is fixed. Please stop fairy tales about <1W tube advantages.

 

[Vespa_SS180]

@MakeMineVinyl , you can build absolutely perfect solid state class A of some 30W/8Ohm with distortion better than -130dB and negligible noise. No SE tube would compete neither in noise nor in distortion. And your horn issue is fixed. Please stop fairy tales about <1W tube advantages.

Such a build would be very interesting indeed. I have never owned a high end solid state amp.
What is clear from my limited experience though, is that my little EL34 SE Class A amp sound a lot better than my present solid state NAD 317. Just wish it had 2*25-30W instead of 2*6.3 W ....!

 

[Doodski]

Such a build would be very interesting indeed. I have never owned a high end solid state amp.
What is clear from my limited experience though, is that my little EL34 SE Class A amp sound a lot better than my present solid state NAD 317. Just wish it had 2*25-30W instead of 2*6.3 W ....!

I've owned a class A to 75 watts output power amp and it sounded lovely. I don't attribute the class A for the sound quality I attribute it's linearity of 75W@8R, 150W@4R and 300W@2R to it's sound quality.

 

[Wes]

The issue is crossover distortion. You might try a listening test focussed righton the power level at the A to B transition.

Calling it a myth without adequate data is surely unwise.

 

[MakeMineVinyl]

@MakeMineVinyl , you can build absolutely perfect solid state class A of some 30W/8Ohm with distortion better than -130dB and negligible noise. No SE tube would compete neither in noise nor in distortion. And your horn issue is fixed. Please stop fairy tales about <1W tube advantages.

You didn't read or soak in the part where the very low wattage is a requirement for the safety of the no-longer-available diaphragms in case some transient gets through the system. These compression drivers are directly attached to the power amplifier in this active system. 30 watts is absolute overkill and dangerous if something went wrong upstream, which could fry the diaphragms or cause them to slam against the phase plug.

You can spout all you want, but these SET amplifiers produce hiss which can only be heard by placing my ear inside the mouth of the horn - I challenge you to find a solid state amplifier (or tube amplifier) which can pull that off with such efficient horns. Please do the research and duplicate this system before speculating what is or isn't possible. The distortion, because of negative feedback is around .02% at the levels I listen at, and that is not far off from what a SS amplifier would do, especially at the sub-1 watt levels involved here.

Remember, I work as an engineer at a company which manufactures audio power amplifiers by the thousands - I have access to everything from consumer class all the way up to very high end amps across several brands, OEM and otherwise; this isn't my first rodeo by a long shot.

 

[BrokenEnglishGuy]

No. It shouldn't be a problem at all.

Nice
my system is r7 + purifi eigentakt 420w 4ohm/ 450 2ohm (?), i need to put my ears at 1- 3 cm to the tweeter level in the night for hear the noise in the uniq ( tweeter ), i dont like these kind of noises

maybe my class D have noise with those horns

 

[MakeMineVinyl]

Nice
my system is r7 + purifi eigentakt 420w 4ohm/ 450 2ohm (?), i need to put my ears at 1- 3 cm to the tweeter level in the night for hear the noise in the uniq ( tweeter ), i dont like these kind of noises

maybe my class D have noise with those horns

Oh yes, just about any amplifier which has not been specifically modified, class D or otherwise, will create hiss which can be clearly audible at my listening position 11' away.

 

[BrokenEnglishGuy]

Oh yes, just about any amplifier which has not been specifically modified, class D or otherwise, will create hiss which can be clearly audible at my listening position 11' away.

the hiss will be lower if the sinad is higher? i mean my power amp have 105dB/108dB, class D

 

[mocenigo]

Oh yes, just about any amplifier which has not been specifically modified, class D or otherwise, will create hiss which can be clearly audible at my listening position 11' away.

What's the sensitivity of your speakers?

 

[MakeMineVinyl]

the hiss will be lower if the sinad is higher? i mean my power amp have 105dB/108dB, class D

The amplifiers my company makes are known for their extremely low noise floors, and generally even then I can hear hiss a couple feet away. This doesn't even begin to be a problem with more typically efficient speakers of around 85db/watt - there simply will not be any hiss with typical systems. In any event, in my particular situation more immediate concerns were low enough power to safely drive the compression drivers, single ended topology so low level grunge like crossover distortion cannot be an issue, the nature of the distortion which is mainly 2nd order which is very benign, and a circuit which can be modified to have very low gain in order to achieve low noise.

 

[MakeMineVinyl]

What's the sensitivity of your speakers?

We're talking about the HF horns/compression drivers, and the sensitivity is 107dB for 1 watt at the efficiency peak in the response.

 

[mocenigo]

We're talking about the HF horns/compression drivers, and the sensitivity is 107dB for 1 watt at the efficiency peak in the response.

ACK, I have had even 110Db at 1W/1m (B&C DCX 50 into Le Cleach horns, hd to use a transformer to make it useable).

But with a Neurochrome buffer into Purifi Eigentakt modules (and transformer bypassed) - no hiss from listening position (3 meters) and barely audible with the head in the horn. This was quite something.

 

[MakeMineVinyl]

ACK, I have had even 110Db at 1W/1m (B&C DCX 50 into Le Cleach horns, hd to use a transformer to make it useable).

But with a Neurochrome buffer into Purifi Eigentakt modules (and transformer bypassed) - no hiss from listening position (3 meters) and barely audible with the head in the horn. This was quite something.

I don't doubt that. My room is very quiet and in a very quiet country neighborhood so that might have something to do with the audibility of hiss in my situation.

 

[SIY]

@MakeMineVinyl do you have a noise density or similar spectrum for your amps? I have some ideas, but would like a baseline.

 

[MakeMineVinyl]

@MakeMineVinyl do you have a noise density or similar spectrum for your amps? I have some ideas, but would like a baseline.

No I don't. Its not very practical to remove the amplifier from the system to do any measurements because the outboard PSU for the filaments is remotely rack mounted and tie-wrapped in. A huge hassle!

Here is a schematic of the modified amp:

 

[SIY]

Understood, I thought you might have done that measurement during development.

Looks like it would be trivially easy to get that noise level from a solid state amp, assuming that the stepdown ratio of the OPT is somewhere in the 20-30 range. What do you use for the output tube filament supply?

 

[MakeMineVinyl]

Understood, I thought you might have done that measurement during development.

Looks like it would be trivially easy to get that noise level from a solid state amp, assuming that the stepdown ratio of the OPT is somewhere in the 20-30 range. What do you use for the output tube filament supply?

Home brew from my parts stash with LM317 regulators in a TO-3 package (floating of course ). This PSU actually gets hotter than the amp I think! In reality, the noise is already so low that I can only hear it with my ear in the mouth of the horn. The LF amp (McIntosh MC240 or Dynaco MK III) is noisier but not much more. Neither is audible more than maybe a foot away from the speaker drivers.