What are the most powerful Pure Class A Amplifiers ever made?

[mep]

The XA.5, XA.8 and XS series each deliver their full rated power as Class A into 8 ohms, double that into 4 ohms. They have an additional 6 dB of A/B power (or slightly more) available above that rating.

I think you are wrong. If an amp gives the specification for how many watts it puts out into 8 ohms in pure Class A, just because the amp can double its power into a 4 ohm load does not mean the watts into 4 ohms will still be pure Class A watts.

 

[rbbert]

I think you are wrong. If an amp gives the specification for how many watts it puts out into 8 ohms in pure Class A, just because the amp can double its power into a 4 ohm load does not mean the watts into 4 ohms will still be pure Class A watts.

Go to the Pass Labs website and/or read any reviews (with measurements) of their products. While your statement can certainly be true in a general sense, it's not true w/regard to the current Pass products.

 

[BlueFox]

I think you are wrong. If an amp gives the specification for how many watts it puts out into 8 ohms in pure Class A, just because the amp can double its power into a 4 ohm load does not mean the watts into 4 ohms will still be pure Class A watts.

Why would they change classes with a 4 ohm load? Are they magic watts?

 

[mep]

Go to the Pass Labs website and/or read any reviews (with measurements) of their products. While your statement can certainly be true in a general sense, it's not true w/regard to the current Pass products.

So you are saying the reviews that include measurements show that the Pass amps double down their power into 4 ohms and they are still pure Class A watts at half the impedance from 8 ohms?

 

[LL21]

So you are saying the reviews that include measurements show that the Pass amps double down their power into 4 ohms and they are still pure Class A watts at half the impedance from 8 ohms?

This is all I could see from Pass site, though did not read thru everything:

"Leaving Class A

The meters on our amplifiers are different. They reflect the current consumption of the amplifier, and when the amplifier is operating, they don’t go down to zero like the meters on other amplifiers. This is because the electrical current consumption of our circuits has a fairly high value at all times, a property called the bias. The bias current runs through the amplifiers at a minimum value, determining the class of operation
– Class B, Class AB, or Class A.

Class B has no bias current, Class AB has a moderate bias current, and Class A has a high bias current. Class AB push-pull amplifiers are hybrids between Class B and Class A. Class AB run Class A at low power levels, and become Class B amplifiers at output currents determined by the bias.

For several years Pass Labs has specified the nominal wattages at which our amplifiers leave push-pull Class A operation into an eight ohm load."

 

[LL21]

Why would they change classes with a 4 ohm load? Are they magic watts?

I believe there is something about the power requirement to stay in Class A all the time that is enormous...I am no techie, but once you get down to 2 ohms or less, you need to be able draw thousands and thousands of watts out of the wall or something, and there is just not enough juice there or something...hence Class A/B which is a more efficient use of the power. I think in Class A, you tend to lose half or more to heat. Again. no techie.

 

[mep]

Why would they change classes with a 4 ohm load? Are they magic watts?

No, it's called magic power. The idle power consumption from Class A is tremendous at their rated power into 8 ohms which is why they double as space heaters into your room. To double that power with pure Class A watts takes one hell of a power supply to pull that off and it would have twice the heat. My Krell KSA-250 is rated at 250 watts into 8 ohms. The amp weighs 140 lbs. The power transformer weighs 83 lbs and it is a 4.3kVa power transformer which is WAY bigger than most power transformers used in any amplifier. That may or may not mean anything to you, but that means it is one hell of a big power transformer. Many people think the KSA-250 puts out 250 Class A watts into 8 ohms and JA from SP speculated that it only is in the 30 watt range.

 

[BlueFox]

I found this on the Pass site. I have the X600.5, which is rated at 80W Class A, 8 ohm. I had assumed it doubled to 160 at 4 ohm, since, until now, I had never heard of the halving syndrome. I guess it is time to email them for clarification. However, no matter the answer, these amps are great.

"So far we have only talked about push-pull Class A bias. Do the effects of high bias also apply to single-ended Class A bias? Yes, but in a slightly different way.

Single-ended Class A bias is where a single gain stage operates against some variety of current source, as compared to push-pull Class A where two complementary stages operate in opposition to each other. Single-ended Class A is often thought of as the “king of Class A” by purists because it delivers the lowest order of harmonic distortion, 2nd harmonic, instead of the 3rd harmonic of push-pull.

It also is the least efficient of the Class A configurations, with an efficiency figure on the order of 20%, sometimes less. A limitation of single-ended Class A operation is that the peak output current is limited to the value of the bias current. By comparison, pushpull Class A can deliver twice the bias current as peak output in Class A, and generally much more than that in Class AB"

https://passlabs.com/articles/leaving-class-a

 

[XV-1]

Chinese brand JungSon JA-200 Reference Class A amplifier is advertised as 200 watts Class A.


http://www.jungson.com/node/25

 

[mep]

Chinese brand JungSon JA-200 Reference Class A amplifier is advertised as 200 watts Class A.


http://www.jungson.com/node/25


View attachment 14060

View attachment 14061

Bitdefender wouldn't allow me to go the webpage that you provided the link to. Big surprise since it is Chinese. Maybe they do put out 200 Class A watts and maybe they don't. I surely don't know what the truth is.

 

[rbbert]

Here

https://passlabs.com/images/uploads/manual/xa.5_specs.pdf

Look particularly at the rows "power output/ch at 4 ohms" and the "leaves Class A". Now you can say these are just manufacturer's specs, but keep in mind that every "independent" test/measurement has always shown the Pass Lab specs to be conservative.

 

[rbbert]

No, it's called magic power. The idle power consumption from Class A is tremendous at their rated power into 8 ohms which is why they double as space heaters into your room. To double that power with pure Class A watts takes one hell of a power supply to pull that off and it would have twice the heat. My Krell KSA-250 is rated at 250 watts into 8 ohms. The amp weighs 140 lbs. The power transformer weighs 83 lbs and it is a 4.3kVa power transformer which is WAY bigger than most power transformers used in any amplifier. That may or may not mean anything to you, but that means it is one hell of a big power transformer. Many people think the KSA-250 puts out 250 Class A watts into 8 ohms and JA from SP speculated that it only is in the 30 watt range.

The Pass Xs150 (mono) weighs 100# for the power supply and 130# for the rest of the amp...

 

[LL21]

Here

https://passlabs.com/images/uploads/manual/xa.5_specs.pdf

Look particularly at the rows "power output/ch at 4 ohms" and the "leaves Class A". Now you can say these are just manufacturer's specs, but keep in mind that every "independent" test/measurement has always shown the Pass Lab specs to be conservative.

Thanks for this...I can see the doubling of watts (not Class A) into 4ohms and the doubling of Class A watts at peak. so I can see how double and double means that the 4ohms Class A rating might therefore be same as the 8ohm Class A rating. I think Gryphon's Class A rating is the same in 4ohms as 8ohms with certain models.

But because I am not sure if 4 ohms to 8 ohms is linear or in some cases geometric or some other kind of logarithmic relationship, is it for sure that the Class A rating into 4ohms is in fact the same as the 8ohm rating?

Thanks...again, not a techie.

 

[Sunnyboy1956]

Hi Lloyd
According to the Wavac site the HE 833 is pure class A all the way to 150 wpc
Cheers
Pradeep

 

[rbbert]

Actually, the way Pass specs their XA.5 and XA.8 amps, the power outputs you see on that table are all Class A watts. The actual power output of all those amps is more than 4 times the rated power (the 6+ dB headroom I mentioned earlier). This isn't a mystery, guys. Read the white papers on the Pass Labs website and look at the specs; you either believe them or you don't. I've never heard or read anything except right here in this topic thread that seriously questions those specs (in fact almost always the opposite) but if someone has measurements or data to post, have at it.

I think the Pass Xs300 (the big brother to rockitman's amps) might be the most powerful Class A amp, with 300/600 wpc @ 4/8 ohms of Class A power before it slides into Class A/B. But OTOH none of Pass Labs current offerings are "pure" Class A.

 

[LL21]

Hi Lloyd
According to the Wavac site the HE 833 is pure class A all the way to 150 wpc
Cheers
Pradeep

Hi Pradeep, yes I have heard this...and in fact, ii nearly considered them when I was looking for an all-out assault tube amp. After a year of searching...I ended up with Gryphon SS Class A...and have never looked back.

 

[LL21]

Actually, the way Pass specs their XA.5 and XA.8 amps, the power outputs you see on that table are all Class A watts. The actual power output of all those amps is more than 4 times the rated power (the 6+ dB headroom I mentioned earlier). This isn't a mystery, guys. Read the white papers on the Pass Labs website and look at the specs; you either believe them or you don't. I've never heard or read anything except right here in this topic thread that seriously questions those specs (in fact almost always the opposite) but if someone has measurements or data to post, have at it.

I think the Pass Xs300 (the big brother to rockitman's amps) might be the most powerful Class A amp, with 300/600 wpc @ 4/8 ohms of Class A power before it slides into Class A/B. But OTOH none of Pass Labs current offerings are "pure" Class A.

thanks...impressive! I think Gryphon Mephisto, which replaced mine as their new flagship reference, is Class A 175 watts 8ohms and 350 watts 4 ohms (175 watts Class A).

 

[rblnr]

My Llano Trinity amps are 200w of Class A hybrid power. They double to 400 into 4 ohms. Great amps, wish the designer was still around.

 

[Audioseduction]

With my PASS Labs xa160.5s I never leave class A.

 

[Orb]

Quick note on Boulder (and Krell). They now have dynamic biasing so that if you are playing at low volumes, they don't suck out the huge currents that standard class A uses. They have an algorithm that then has to anticipate when to dial this up or down.

Yeah and they are not the only ones these days, although how each does it can be subtly different (temp/voltage-current requirements/etc)

I say get more efficient speakers if one wants pure class A
Heat would be a nightmare at high watts.
Cheers
Orb