Class A Watts ?

[Hyfi]

1500wpc Class A Monos, no fans. Only $245K for the pair

 

[infullview]

1500wpc Class A Monos, no fans. Only $245K for the pair

So 1500watts at a relative efficiency of 25% for class A they would require a 50 Amp circuit to provide an input of 6000 watts. I think you might have an extra zero somewhere.

 

[whoaru99]

Looks can be deceiving but to me doesn't look like enough fin for 1500W pure Class A. Perhaps one of the sliding bias type designs?

 

[Hyfi]

So 1500watts at a relative efficiency of 25% for class A they would require a 50 Amp circuit to provide an input of 6000 watts. I think you might have an extra zero somewhere.

https://sightandsoundgallery.com/products/boulder-3050-mono-1500w-class-a-power-amplifier

 

[mad shadows]

I take the amp with the biggest power supply. 9/10 that will be the class a amp.

 

[fill35u]

So 1500watts at a relative efficiency of 25% for class A they would require a 50 Amp circuit to provide an input of 6000 watts. I think you might have an extra zero somewhere.

The big Boulder amps run off 240V line power.

An important note, the harder you drive a Class A amp, the *less* heat it dissipates. Of course, that energy is still going somewhere, and that's to the speakers. The speakers are still warming your room, as most of the energy is turned to heat in the motor. The sound energy (with the exception of the low bass passing through your walls and warming the neighborhood) turns to heat in your room as well.

Crossover distortion is pretty awful stuff. Any decent Class AB amp will have it reduced well below audibility, though. I suspect any audible benefit of Class A in comparison might be to poorly designed AB amps that test well on the bench, but suffer from dynamic thermal distortion. The optimal bias point changes with temperature, and loud passages that cause rapid heating of the transistor die might reveal crossover distortion during following quiet passages. Even with bias components mounted an inch away from the outputs on the same heatsink, thermal inertia causes a time constant on the order of several seconds. ThermalTrak devices mitigate this, but interesting that there's been no standard test for this performance, and AFAIK no formal study for audibility.

 

[Hyfi]

Here is a decent tutorial on Classes

https://www.electronichouse.com/home-audio/the-amplifier-class-divide-amplifier-types-explained/

 

[rothwellaudio]

A good class A amp is biased generously, has a bit more voltage than it really needs, and are universally rated by their builders by their bias. I think it's much more descriptive of the amp and that's what buys and builders of them are designing and paying for.

Show us three examples of commercial class A amps that don't have specs for power output but do have specs for their bias current (or bias voltage, or bias power or whatever you consider bias to be).

 

[infullview]

The big Boulder amps run off 240V line power.

An important note, the harder you drive a Class A amp, the *less* heat it dissipates. Of course, that energy is still going somewhere, and that's to the speakers. The speakers are still warming your room, as most of the energy is turned to heat in the motor. The sound energy (with the exception of the low bass passing through your walls and warming the neighborhood) turns to heat in your room as well.

Crossover distortion is pretty awful stuff. Any decent Class AB amp will have it reduced well below audibility, though. I suspect any audible benefit of Class A in comparison might be to poorly designed AB amps that test well on the bench, but suffer from dynamic thermal distortion. The optimal bias point changes with temperature, and loud passages that cause rapid heating of the transistor die might reveal crossover distortion during following quiet passages. Even with bias components mounted an inch away from the outputs on the same heatsink, thermal inertia causes a time constant on the order of several seconds. ThermalTrak devices mitigate this, but interesting that there's been no standard test for this performance, and AFAIK no formal study for audibility.

So your argument is that the instantaneous junction temperature changes bias requirements faster than can be adjusted for by the colocated diode on the heat sink, interesting. So you would need to devise a test that would burst a sine wave at high volume and measure distortion before the heat can be dissipated into the heat sink.

 

[E-Stat]

An amplifier is normally rated at the maximum continuous power it can deliver into a load at a specified distortion rating, independent of any bias.

While that's the norm, Nelson Pass goes the opposite way of most and understates maximum output. RL uses one of his First Watt clones.

Note JA's measurements as to the maximum output of the 30 watt per channel XA-30.

https://www.stereophile.com/content/pass-labs-xa305-power-amplifier-measurements

A watt is a watt, but amplifiers in my experience vary widely in their dynamic ability when playing music.

 

[Blue Shadow]

1500wpc Class A Monos, no fans. Only $245K for the pair

AK doesn't play much in the true class a sandbox that often. Lots of brands we don't read about on these pages have offerings. too new to be vintage. started too expensive to ever be cheap.

 

[Hyfi]

AK doesn't play much in the true class a sandbox that often. Lots of brands we don't read about on these pages have offerings. too new to be vintage. started too expensive to ever be cheap.

I know, but they need to be exposed to what is out there. Some may even want to go to a HE B&M and actually listen to a killer setup just for personal reference. I am driving from PA to Naples FLA in a month and will be stopping at Suncoast Audio in Sarasota to see some high class systems like this.

 

[E-Stat]

Looks can be deceiving but to me doesn't look like enough fin for 1500W pure Class A. Perhaps one of the sliding bias type designs?

Yes, it is.

"Class A Bias
The 3050 has an intelligent biasing scheme that continuously measures voltage draw, current draw and load at the output terminals. The scheme then instantly raises the output section's bias fast enough to keep any transients or dynamic swings in Class A operation and then ramps the bias down in a gentle analog fashion over a period of 28 seconds until the next transient is detected that will require raising the bias again. This scheme makes the amps much more efficient and reliable than traditional full-bias Class A amps but without the audible steps or sliding schemes."

http://www.enjoythemusic.com/magazine/equipment/1011/boulder_3050_monoblocks.htm

A fixed bias class A design like the Pass Labs Xs300 is much heavier per watt (300 watts/268 lbs vs 1500 watts/450 lbs) than the Boulder.

 

[spark1]

If you have super efficient speakers, you don't need 200wpc. You can easily get away with a 50wpc Class A and have no idea it isn't more powerful.

The same would be true of a 50 watt AB amp.

 

[rothwellaudio]

So your argument is that the instantaneous junction temperature changes bias requirements faster than can be adjusted for by the colocated diode on the heat sink, interesting. So you would need to devise a test that would burst a sine wave at high volume and measure distortion before the heat can be dissipated into the heat sink.

It's well-known that bias circuits don't track the junction temperature of output transistors very well and there's a time lag. However, Sziklai pairs of output transistors don't need fast thermal tracking to remain stable, so it is possible to get round the problem. Also, there have been output transistors which incorporate the temperature sensing diode inside the body of the transistor, and they track much better.

 

[fill35u]

So your argument is that the instantaneous junction temperature changes bias requirements faster than can be adjusted for by the colocated diode on the heat sink, interesting. So you would need to devise a test that would burst a sine wave at high volume and measure distortion before the heat can be dissipated into the heat sink.

Well, it's not my argument whether the effect happens or not- it's been demonstrated and measured. The fact that ThermalTrak devices were developed and used also shows that the problem has been known and addressed.

But yes, I think a test like you describe is needed to standardize amp performance in this area. There have been standard burst tests, but AFAIK they only measure performance *during* the burst, not immediately after.

Of course, the most important question is *audibility*. FWIW the stapedial reflex recovers in a fraction of a second, whereas the bias point might take 30 seconds to fully stabilize. But does anybody notice if Stravinsky sounds better in Class A? Skrillex probably not so much.

 

[fill35u]

I take the amp with the biggest power supply. 9/10 that will be the class a amp.

How do you figure that of all the amps ever offered, the top 90% with the largest wattage power supplies were Class A designs?

And since you always chose the biggest power supply, how do you like your Pivetta Opera amplifier?

 

[mad shadows]

How do you figure that of all the amps ever offered, the top 90% with the largest wattage power supplies were Class A designs?

And since you always chose the biggest power supply, how do you like your Pivetta Opera amplifier?[/

Class a amps tends to have bigger power supplies, the rest is opinions.

 

[fill35u]

Class a amps tends to have bigger power supplies, the rest is opinions.

Can you present any facts to back up your opinion?

 

[infullview]

Well, it's not my argument whether the effect happens or not- it's been demonstrated and measured. The fact that ThermalTrak devices were developed and used also shows that the problem has been known and addressed.

But yes, I think a test like you describe is needed to standardize amp performance in this area. There have been standard burst tests, but AFAIK they only measure performance *during* the burst, not immediately after.

Of course, the most important question is *audibility*. FWIW the stapedial reflex recovers in a fraction of a second, whereas the bias point might take 30 seconds to fully stabilize. But does anybody notice if Stravinsky sounds better in Class A? Skrillex probably not so much.

I have to say this thread has been an eye opener for me. Lots of new info I hadn't thought of or about to now consider concerning class A amps. And yes, Skillex is distortion by definition for sure