[RDavidson]

Thanks QE. Actually, this thread started getting off track as a "personal definition" came into play much earlier. I questioned it, despite my limited knowledge (particularly on the technical specifics). Roger stepped in and cleared the air. I mistakenly thought you were applying another "personal definition" into the conversation, but you weren't.

That's something I really like about AC. People here, in most cases, are respectful. Simple misunderstandings can be easily resolved without getting into stupid, pointless, bickering and arguments.

Back to the topic........other examples.......?
I stated Pass Labs a long time ago. Someone else mentioned First Watt. Maybe it goes without saying, noting the other two, but Threshold is another example as well as the spin-off Stasis designs Nelson did for Nakamichi.

[Roger A. Modjeski]

Please correct me if I'm wrong here, but I believe at least some GAS amps (Ampzilla) are SE Class A.

I owned an Amzilla, have had many visits with James B., know his work well and I can assure you GAS never made any single ended amps. James never mentioned SE amps and I would be surprised if he ever would in any positive way. He was not an SE guy. His interest was always good specs, low distortion, high damping; good sounding classic design. Smart guy, I miss him. His early work was at SAE and all those amps were push-pull class AB which is written AB not A/B.

To clarify: All SE amps are class A.  They cannot be otherwise. (Some are A2 where the grid goes positive, but these are rare and that would not apply to solid state, there is no grid.) Due the heat from high bias they are usually not made at high powers. The output of a class A SE amp cannot be more than 1/2 its dissipation and is usually about 1/3-1/4. To my knowledge there are far more examples of SE amps made with tubes than transistors, though transistor SE amps are more efficient as the transistor has a very low saturation voltage compared to a tube. In the tube realm a pentode will be more efficient than a triode and can be close to the efficiency of a transistor. But again, SE amp makers like triodes for their linearity, low output impedance and historic significance.

I knew John Bedini personally and I believe his amp was class A to 25 watts. I am almost certain it was push pull. Again it was low power at 8 ohms. For those who missed my rather long post, the problems of large class A amplifiers either push-pull or single ended are covered in two rather large posts near the end of the first page of this discussion.

[Freo-1]

Speaking of Class A amps, I just got in a Electrocompaniet AW2-120 that runs Class A.  Electrocompaniet makes some the best sounding solid state sounding gear available at any price.  The amp has outstanding clarity, and exhibits virtually none of the artifacts associated with solid state electronics.  It displays better dynamics than many other solid state amps that have more rated power. 

Electrocompaniet has proprietary circuitry that addresses Transient Inter-modulation Distortion (TID) for solid state amps, and trust me when I tell you, it works in spades.  The AW2-120 has all the positive aspects one would expect from Class A, and some of the cleanest sound available at any price point.


Transient intermodulation distortion, or TIM (TID), occurs in amplifiers that employ negative feedback when signal delays make the amplifier incapable of correcting distortion when exposed to fast, transient signals.

http://www.ka-electronics.com/images/pdf/Leinonen_Otala_Curl_TIM_Measurement.pdf

[RDavidson]

I owned an Amzilla, have had many visits with James B., know his work well and I can assure you GAS never made any single ended amps. James never mentioned SE amps and I would be surprised if he ever would in any positive way. He was not an SE guy. His interest was always good specs, low distortion, high damping; good sounding classic design. Smart guy, I miss him. His early work was at SAE and all those amps were push-pull class AB which is written AB not A/B.

Do you know if James ever designed any amps at GAS or Sumo that were push-pull class A, or was this basically where Nelson really came into the picture in terms of historical solid state design significance?

[Roger A. Modjeski]

Speaking of Class A amps, I just got in a Electrocompaniet AW2-120 that runs Class A.  Electrocompaniet makes some the best sounding solid state sounding gear available at any price.  The amp has outstanding clarity, and exhibits virtually none of the artifacts associated with solid state electronics.  It displays better dynamics than many other solid state amps that have more rated power. 

Electrocompaniet has proprietary circuitry that addresses Transient Inter-modulation Distortion (TID) for solid state amps, and trust me when I tell you, it works in spades.  The AW2-120 has all the positive aspects one would expect from Class A, and some of the cleanest sound available at any price point.


Transient intermodulation distortion, or TIM (TID), occurs in amplifiers that employ negative feedback when signal delays make the amplifier incapable of correcting distortion when exposed to fast, transient signals.

http://www.ka-electronics.com/images/pdf/Leinonen_Otala_Curl_TIM_Measurement.pdf

Hi Freo,

I know the company, have owned their excellent amps. I had the first one which came from the work of Matti Otala. I sought him out at CES many years ago and had a nice lunch with him. A very sharp guy who found something people were not yet thinking about. The AES paper was written for engineers.

In reading the last page of the manual I see: Due to high class A operation in all Electrocompaniet designs, it is normal for the
AW 2x120 to feel warm. Proper ventilation is important.. From this statement I infer the amp is not full class A but just high class A. How high is high. Using Nelson Pass's estimate of dissipation = 3 times total power the amp should draw 720 watts (120 per channel x 2 x 3).

I did a little figuring for a perfect lossless amp and came up with a theoretical number of dissipation = 2x idle power. But that does not include power transformer losses, rectifier losses, transistor saturation losses and the big one, how close to the rail can the out put get for any particular load. This is the biggest practical loss which brings the theoretical 2x to approach Nelson's 3x. In 1976 I designed a bridged amp to run off 13 volts in a car. I was very careful to maximize the output potential and got within about 0.2 volt of the 13 volt rail and 1 volt above ground. That amp would be like a 2.1x dissipation to output amp.

I wrote my first post here not so much to get into a discussion of who makes class A amps  but what a class A amp has to do to be a class A amp so that the reader could tell who was telling the truth . Everyone wants a class A amp. We want grade A meat, produce, milk and eggs. Manufacturers of amplifiers know we desire class A amps (frankly I  don't desire them because of their power consumption). I don't know how well the USDA is monitoring our food quality but no-one is monitoring amplifier claims to be class A. That is why I wrote that extensive post so you the buyer could determine who was telling the truth.

The OP asked "who makes amps with class A bias" I don't think we have found one yet. They do exist but you will likely find them in lower power ratings simply because of the high dissipation.

[Roger A. Modjeski]

Do you know if James ever designed any amps at GAS or Sumo that were push-pull class A, or was this basically where Nelson really came into the picture in terms of historical solid state design significance?

I don't think James did any class A, amps. He was a class A guy however.

Nelson is the only guy I know who has taken the time to write up a paper on class A bias. From his website: The XA.5 amps are Class A (low rail voltage and high bias current) and the X.5 amps are high bias AB (high rail voltage and lower bias current). Note that the XA series says just what I have been saying, you need low rails and high bias to make a practical class A amp. His 30 watt per channel draws 200 watts. This is an excellent paper from Pass Labs. https://passlabs.com/articles/leaving-class-a

Below the table of information on the various amps he states. "Push-pull amplifiers generally operate in Class A mode up to a point where the output current is twice the value of the bias current. In the Class A region, both halves of the circuit share the signal simultaneously. Beyond that the signal is handled solely by the push (+) half of the amplifier or the pull (-) half." This is true for transistor circuits, tubes behave differently.

Later he states "As a practical matter, this means that our X (Class AB) amplifiers are biased to dissipate roughly half of their rated output power. The XA (Class A) amplifiers are biased to dissipate roughly three times their rated output power." His 30 watt per channel (60 watts total) dissipates 200 watts. You have to be rather careful reading the comparative amps as some are stereo and some are mono. For example the XA30 is 30 per channel and the XA60 is 60 mono. Both draw 200 watts. The idle current is higher on the 60 watt mono by 1.4 times, exactly what it should be. It's nice to see some information where the numbers are right, its rare.

[G Georgopoulos]

I dont know why Nelson makes them?..Are they that good?
I like class a of tubes but no of solid state...

Power amps should be designed with the highest of efficiency,it's good for the planet..!!!

other technologies should be considered for ss such as class-b...!

[RDavidson]

I dont know why Nelson makes them?..Are they that good?
I like class a of tubes but no of solid state...

Many share the same feeling as you. Personally, I don't care if an amp is tube or solid state, as long as it sounds good. As Nelson has gained quite a following, including many tube lovers, all I can say is that you should seek out his amps and listen for yourself. If you get the chance to hear a Pass Aleph 3 or Aleph 30 (which are modern classics) you'd understand.

[G Georgopoulos]

Have you ever build a class-a?the power they consume is HUGE!!!
as for nelson i have the greatest of respect!!

[RDavidson]

Have you ever build a class-a?the power they consume is HUGE!!!
as for nelson i have the greatest of respect!!

No. I don't have the skill to build an amp on my own......though some day I'll probably take some classes, then give it a try.

Yes, inefficiency is a trait of Class A (both solid state and tube).

While not "good for the planet" I really don't think there are enough people on the planet using excessive energy (powering their Class A amps) to make a significant negative impact on the environment. For those concerned with the power usage of their amplifiers, there are MANY others to choose from.......but they won't sound like Class A either. Good thing we have choices vs all manufacturers producing Class B as you suggest.

[opnly bafld]

Have you ever build a class-a?the power they consume is HUGE!!!

From the First Watt FAQ page:

"Frequently Asked Questions

Q: Isn't Class A bad for the environment?

A: Everything is bad for the environment, in case you haven't noticed. When I look at the cost of enjoying my 25 watt/ch class A amplifier as compared to watching a big screen television or running a porch light all night, I see that I get as much or more value for the same sort of consumption. If I drive down the hill to shop at Fry's, I consume about as much power as running one of my amplifiers for 2 hours a day for a year. So I go to Fry's less often, and I turn the amp off when I'm done."

........and then there is this:

While not "good for the planet" I really don't think there are enough people on the planet using excessive energy (powering their Class A amps) to make a significant negative impact on the environment.

[Roger A. Modjeski]

Isn't anyone building a sensible 10-20 watt Class A transistor amp these days? At that power level things are reasonable and its enough power for many applications. With today's more sensitive speakers a few watts gets plenty of sound for my ears. Keep in mind this will only appeal to those who know that you don't need but so much headroom. For 1 watt average I believe 10 watts is adequate. Good amps are low distortion right up to clipping. Headroom is over-rated by those who don't understand what is really going on in amplifiers. I invite anyone to give me a cogent argument why one needs a 100 watt amp to play a few watts.

A note on clipping: I have a scope in my music rack and turn it on often to see where I am in relation to clipping. I have found with many good listeners that slight clipping a few percent of the time is not noticed. This notion that we need a 100 watt amp to play 1 watt needs to be dispelled. 

When it comes to playing CDs or a music sever the headroom can be calculated precisely. A CD player puts out 2 volt period. It can all be figured from there.  With a proper gain amplifier (no preamp needed) one could set up the volume control so that at full volume the amp would never, ever clip because it couldn't

[G Georgopoulos]

From the First Watt FAQ page:

"Frequently Asked Questions

Q: Isn't Class A bad for the environment?

A: Everything is bad for the environment, in case you haven't noticed. When I look at the cost of enjoying my 25 watt/ch class A amplifier as compared to watching a big screen television or running a porch light all night, I see that I get as much or more value for the same sort of consumption. If I drive down the hill to shop at Fry's, I consume about as much power as running one of my amplifiers for 2 hours a day for a year. So I go to Fry's less often, and I turn the amp off when I'm done."

........and then there is this:

ok, please accept my sincere apologies...

however if your electricity bill raises don't blame me there as well...

[G Georgopoulos]

Isn't anyone building a sensible 10-20 watt Class A transistor amp these days? At that power level things are reasonable and its enough power for many applications. With today's more sensitive speakers a few watts gets plenty of sound for my ears. Keep in mind this will only appeal to those who know that you don't need but so much headroom. For 1 watt average I believe 10 watts is adequate. Good amps are low distortion right up to clipping. Headroom is over-rated by those who don't understand what is really going on in amplifiers. I invite anyone to give me a cogent argument why one needs a 100 watt amp to play a few watts.

A note on clipping: I have a scope in my music rack and turn it on often to see where I am in relation to clipping. I have found with many good listeners that slight clipping a few percent of the time is not noticed. This notion that we need a 100 watt amp to play 1 watt needs to be dispelled. 

When it comes to playing CDs or a music sever the headroom can be calculated precisely. A CD player puts out 2 volt period. It can all be figured from there.  With a proper gain amplifier (no preamp needed) one could set up the volume control so that at full volume the amp would never, ever clip because it couldn't

Roger i have thought of it too, people's taste in big amps will remain no matter what i say,most people will confuse power o/p between class-a and other class amplifiers.

[Architect7]

Wasn't it Jim Salk that showed how transients were clipping a lower powered amp and when matched with a bigger amp, consumption soared to 300w during intense passages?

That and I hear a clear difference between using the 75w from my receiver and my 360w Rotel amps.  Even though my line arrays are around 99db/1w efficient.  Any explanation for this would be great.

[macrojack]

There are low power Class A amplifiers out there though I could not provide a comprehensive list. Richard Brown of BEL amplifier fame made his 1001A amplifier in California for over 30 years before his death a few years ago. It put out 50 watts in stereo Class A power. Sugden, a British maker, has produced a low power (20 watt?) Class A amplifier in integrated form and as a stand alone power amplifier for about the same time. Nelson's Forte line offered something similar. There was the Levinson ML 2. My Aleph 0 amps were Class A mono blocks at 60 watts each. Surely there were many others that I am not recalling or never knew about. It's been done aplenty.
Use of highly efficient speakers may seen unwise or unnecessary to some of you but, aside from real and realistic energy concerns, there are also personal benefits that might prompt you to do the right thing. Given a restricted budget for amplification, which nearly all of us must recognize, there is more refinement available for $3000 at 50 watts than there is at 500 watts. The exception to that rule, and the obvious answer for those who can see it is Class D. New versions from Hypex, Pascal, Abletec and B&O Ice Power are showing up in amplifiers from many different established and newer companies.
I have a very efficient pair of horns with 50mm compression drivers mounted on top of 5 cu. ft. cabinets with outboard passive crossovers resulting in about 98 db efficiency. I'm driving them with a Jeff Rowland Design Group Continuum S2 integrated amp rated at 400 watts per channel. Obviously I do not need that sort of power in my living room. On the other hand, the combo sounds utterly glorious, uses very little power and never gets hot. So what's the harm?
In the past I have owned the BEL amplifiers, the Aleph 30 and the Aleph O monos. If memory serves, none of them had anything on my present amplifier. Maybe an honest look at what is available today in Class D amplification would obviate the quest for Class A for some, if not all, of us.Check it out. Certainly a lot of ACers have found happiness with the Hypex NCore amps. And Freo-1 even found a Yamaha Class D that he loves. This matters because I can think of no louder proponent of Class A than he has been on this forum.

[barrows]

The obvious answers which come first to mind are the XA.5 and XA.8 series amplifiers from Pass Labs, and Clayton amps.  MSB's big monoblocks appear to be fully class A.
One brand I have not seen mentioned in this thread is Vitus; they make some glorious sounding amplifiers, both pure class A models and higher power class AB models.
If one is really concerned with power consumption, my advice would be to either get some efficient speakers and go with something low power like a Pass XA 30.8, or, go to the other extreme, and end up with a well implemented Ncore class D amp.  With good system matching, a well massaged Ncore amp can sound very, very good.

[mboxler]

The OP asked "who makes amps with class A bias" I don't think we have found one yet. They do exist but you will likely find them in lower power ratings simply because of the high dissipation.

They have been sold out for a long time, but would these qualify?

http://www.diyaudio.com/store/amplifier-kits/amp-camp-kit-23/aca-bundle-210.html

I built a pair, but have yet to find the right preamp, speaker setup.

Mike

[Doublej]

Monarchy Audio has some. Plinius did in the past, I don't know if anything currently available is class A.

[WGH]

Unfortunately discontinued, Jim Hagerman's Cymbal was an 8w mono all tube class A amp.
http://www.hagtech.com/cymbal.html

The Cymbal featured:
    All vacuum tube topology
    Pure Class A amplifier stages
    No feedback
    No hum
    Differential input stage
    Low output impedance
    Vacuum tube B+ rectification
    Choke regulated B+ 

The Cymbal manual which includes the schematic and parts list is still available: http://www.haglabs.com/pages/archive