??? WHY WHY WHY ??? Class A vs Everything Else

Yup, once you get hooked on class A, it’s difficult to enjoy anything else. In the past few years, I’ve tried several class A/B and class D amps at many price points. I always find my way back to class A. Enjoy!

You can thank the designer, not the class of amplifier. People think Class A is the best like it's a report card. An A is better than B, and don't get me started on Class D. That's barely passing. I think of Class A similar to driving my car with the gas to the floor, and using the brake to control my speed. Soon the engine will overheat and the brakes will wear out.

Nice! Hang on to that amp. 

Second order harmonics are like a butter drizzle. Who can resist it and why should they?

I read an article about a second order harmonics generator by Nelson Pass after i built his Korg Nutube preamp from diyaudio. In the article he explains very clearly how phase matters when it comes to 2nd order harmonics.
I’ve been listening to the the preamp all day and I really like it but i wanted to see how it would sound if i flipped the phase. I listened to a handful of songs and quickly noticed i was not nearly as relaxed I was before. I could hear some subtle differences in the music but i was definitely much more focused on how anxious i was all of sudden. I powered down my amp and rolled the banana plugs back and listened to the last two songs again. It made a difference almost immediately, i calmed back down and it almost felt like the music slowed down a bit. There’s certainly a chance this is all placebo effect but i figured it was worth writing this up to see if others have had experiences like this. I couldn’t find anything on

https://audiokarma.org/forums/index.php?threads/2nd-order-harmonics-phase-and-anxiety.1054032/

The sound is like the colors of nature,as the rising sun just clears the horizon & suddenly everything snaps into vivid focus,taking your breath away...

Nice. I think Srajan Ebaen has a spot for you on the payroll at Six Moons.

@mapman you mean the same CORRUPT,BIASED,OVERREACHING courts blocking WE THE PEOPLES MANDATES right!
@immatthewj +10000 & then the DEMONcrats like mapman have to pile on!

@freediver the other thread "Import Duties Are Happening" was closed but just to be clear I am not a Democrat as you indicated.  Also even if I were that would not make me a "demon".   Not jumping to conclusions is a good practice. Also a good idea not to demonize entire groups of people as you clearly did.    Cheers!

Also sad that posts simply stating the facts some may not like get deleted but hate mongering ones like that remain for all to see.  Oh well que sera sera.

WTF?? where did that come from?

Does someone have Tourettes?

In my experience there's a purity to the sound of class A amplification that you don't get with other classes.  My first experience with a pure class A amplifier was a Classe Audio DR-3 VHC the VHC standing for very high current.  The DR-3 VHC was a more powerful version of the DR-3 putting out 45 wpc vs 25 wpc in the standard DR-3.  The DR-3 VHC was designed by the founder of Classe Audio, David Reich (hence the DR in Classe Audio's products).  It sounded great with the matching DR-5 preamplifier I was using in my system at the time.  There's just something pure about a Class A circuit.  I really enjoy the Schiit Asgard 2 with my planars and I'm sure that it's the A2's Class A circuit that makes this combination work so well.

IME, Class A is more like graceful overengineering. May not be practical for all scenarios, but beautiful when done right. Some may call it inefficient (compare Class A/B or D) and while Class A runs warm to hot; it offers a purity and immediacy that many of us find musically addictive.

You can thank the designer, not the class of amplifier.

This.

As long as the amp has a decent distortion signature it will sound pleasing regardless of the class of operation. 

There are now class D amps that rival the best class A tube and solid state amps. And there are many that do not. Its all about the designer's intention. 

I used to own a Sugden FBA 800 amp and while it had some very nice qualities, it lacked the requisite dynamics (for me) for orchestral music, plus it ran very hot!  I sold it and purchased a 300 watt class A/B amp which was okay but I sold it after about a year or so. I finally purchased a pair of class D mono's and now I am very satisfied!

FYI - my speakers are DeVore Super Nine's, so hardly a difficult load to drive.

"There are now class D amps that rival the best class A tube and solid state amps."

I've never heard a Class D amp that rival my Pass XA25 or the Sit 3,  but maybe I need to hear much better class D amps! I heard Atmasphere's with some Tektons but it was unlistenable; I blame the speakers and the room, though. So, not a fair trial.

I agree on class A generally sounding better than most other types of amps. Years ago I had a White Audio Labs 100 watt / side class A power amp & it sounded really nice but of course was a beast & drew 5 amps at all times much of which went up in heat. Currently, my Rogers integrated does about the same & also sounds great. 

@mapman 

Wow. You came into a totally unrelated thread to respond to a post in a closed thread? You might need to relax a little....

I have a totally unique class a integrated amplifier hand made in ITALY 

Pathos Audio. Their Top inpol class a has its own very unique patent

it takes the 12au7 tubes and amplifies this as part of the signal path 

the 12ax7 tubes to a lesser extent mainly for the preamp section 

for a 45wpc -8 ohms, 70wpc 4 ohms and 86 lbs it’s a beautiful to look at and 

sounds like a SET AMP WITH SS detail and control , using vintage nose RCA ,as well as AMPEREX  tubes it sounds well above $11800 price point , the preamp section 1% or better resistor ladder and relay control preamp section 

this INPOL2-MK-2= integrated  from Upscale Audio is a true DUAL mono design just sharing a power cord at 86 lbs a totally unique design using 6 Big MOSFETS per channel on the outputs . I actually sold these while in the U.K 20 years ago this NEW Mk2  even more so good for speakers 89db or better 4 ohm even more current I use a very good AQ HURRICAINE power cord to a dedicated line all FURUTECH CONNECTORS .  A NICE CHANGE OF PACE IT DRIVES THE FOCAL SOPRA-2 Loudspeakers very nicely I may be trying the QUALIO ULTRA LOUDSPEAKERS TO COMPARE TO  FROM OUR AUDIO CLUB . 

WITH AUDIO ITS ALWAYS SOMETHING NEW!!

It may just be jumping ahead a few years in amp design, but my two Pass Labs XA30.8 and the two X260.8 (monos)  in a tri-amped configuration never come out of class A.  And my rig has never sounded better.  Yes I have pushed it to very loud and the meters have yet to move an iota!   Headroom baby! That's where its at.

Regards,

barts

Wow put it in in storage at a friends or similar, it’s not big equipment won’t take a lot of room and then you won’t have to spend pages of a long story for a simple issue.

Cheers 

More like taking the Bentley on the school run.

I think of Class A similar to driving my car with the gas to the floor, and using the brake to control my speed.

Class A has positive attributes but you do give up stuff like high power often needed by some speakers and of course there's the heat. Like the real world it's different compromises which vary with your taste in sound and your system.

By the way you often see reviewers citing a preamp is class A. It means they don't know how preamps are designed. All preamps are class A because it's easy on a differential preamp since there's so little current involved. And single ended preamps have to be class A: their topology can only be class A.

I might add that as above all single ended amps are class A. But almost every push/pull class A amp eventually goes into class B at very high output. And the class A portion goes down with lower output impedance for solid state amps. The only exception I know is the old Mark Levenson ML2 amp which doubled power down to at least 2 ohms and remained in class A. And it was the biggest 25 watt amp I've ever seen.

Class A-ish tends to sound the best,,,

Here’s a more technical discussion on it from the engineers at Schiit Audio

https://www.youtube.com/watch?v=_rSQCqqTk4E&t=1534s

But, if your HVAC kept kicking on in the summer and the noise floor in the room went way up...oh well...

They all sound great to me but lately I have been a fan of Class D/GaN amps. Crack out the class A stuff in the winter. 

All the amps these days have such good components in them that they all sound much better from amps a decade ago unless they cheated out on the components.i amp roll alot and that's half the fun.then there is the sandbox some synergy is better with some components.the gain,feedback ,impedence,ect all have to get along in the sandbox. When the force is correct from star wars it's exciting.nurvana class a a/b d and h .love it all. Now let's talk cables that should get the party 

I built a Hiraga Super 30 Class A amp. It is the amp I listen to most, just does everything well. Lots of detail, without being fatiguing. Amazing 3d soundstage, with clear imaging. Rich mids and tight bass. Is very responsive to upstream components, showcases differences in the front end. Works well with most of my speakers, though it’s too much with my Cornwalls in the low end - my Type 45 plays better with those. 
 

One thing I noticed, is how well it plays at low listening levels. 
 

I would love to get my hands on a GanFet Class D amp, so I could compare the two. I have class A tube and solid state (single ended and push pull of both). Several different types of amps based on different output tubes. 
 

They all have their “thing”they do well. And depending on what I’m listening to, speakers and amps will be swapped in and out.

But is the Hiraga I keep coming back to. 

Something about Class A, something about Sugden.  I've owned/own 5 pieces.  Only one that disappointed was an A21SE CD player.  Not!!!  Have fun.

The choice between Class A operation vs Class AB comes down to a simple decision between:

(A) Inherent low distortion and absence of device switching over the entire waveform, and also the least efficient mode of operation.

(AB) Significantly higher efficiency, greater power output (typically 3X or more) and an implied requirement for local or global feedback to linearize the switching transition in the output devices.

So if you’re building a transistor or tube power amp, the only difference from a design perspective is the rail or B+ voltage and the operating point for the output devices. Class A operation involves lower voltages but a high standing current ... in effect, the amplifier draws the same amount of power from the AC line, whether it is idling or at clipping. So it runs hot all the time. They are room heaters, thanks to low efficiency.

Class AB has the interesting property that AC power draw varies with signal level; this has implications for power supply design, since current flow through the supply is program modulated, and not in a simple way. This is a roundabout way of saying Class AB amplifiers need better power supplies, and full regulation isn’t a bad idea. Otherwise, 100/120 Hz rectification buzz in the audio signal will be program modulated, which is extremely undesirable.

There is an additional complication which applies to solid-state but not tube amplifiers. Tubes don’t need heat sinks, since device characteristics are not affected by operating temperature, and they are designed to radiate heat on their own without assistance.

Transistors can be destroyed by high device temperature, or have their useful lives shortened. The failure mode is complete destruction, which happens without warning, and might expose the loudspeaker to full rail voltage, which will destroy it.

In practice, transistor amps operating in Class A need substantial heat-sinking and effective temperature monitoring to prevent runaway thermal faults. These additional circuits must be highly reliable, since runaway thermal faults will destroy the output section before the user can get to the power switch.

In tube amps, Class A versus Class AB is a simple decision between power output versus linearity. Not much to it. In transistor amps, in addition to a significant power derating, Class A implies good thermal management if the amp is to be reliable.

In practice, transistor amps that operate in true Class A are thermally limited. How big a heat sink will the consumer accept, and are fans acceptable?

(Note: there are various sliding-bias schemes, which have been around since the Seventies, that claim to be Class A. They’re not. Non-switching is not the same as Class A.)

For some reason, Doug Dale has figured out how to design my (his) Coda s5.5 amp which produces 50 wpc class A into 8 ohm and 100 amp current so that it is not very warm to the touch and really makes very little heat. You can comfortably place your hand on the amp and leave it there. The heat sync seem to not be very warm either. It's a rather powerful little amp for what it is. Oh, and it sounds wonderful to me.

As an owner of an Esoteric A-03 Class A has many virtues but also some shortcomings. Dynamics/Headroom are minimized due to lower power and the relaxed sound of Class A. Transient Speed and Bass Slam can also be effected. Many Class A amps have an oversaturation(IMO) of color Accuphase/Pass Labs to name of few. Be careful of buying a Pure Class A integrated due to excessive heat entering the Preamp section. Even with these issues Class A amplification can provide the most coherent and balanced sound available. IMO the best Class A strength is the Non-Mechanical flow of music that only the best Class AB power amps can approach. 

Listening at lower volumes as I do nowadays, can’t I have it all with a class A/B amp that is biased 10-15 watts to class A?

My BHK-300 amps are biased @10 watts class A and I rarely go over, but when I do, it’s great to have the extra power.  Think Tricycle by Flim & The BB’s.

@zlone I thought you could,that's why I got the SimAudio 240i,but swapping between that & the Sugden the last few days says no you can't..I don't know if that first 10 watts gets used up too quickly or it's something else but it just doesn't have that same lit from within texture at all volume levels the Sugden has...

@freediver    +1 There is no substitute for pure Class A. Biased based Class A is more of a sales ploy than performance based.

(AB) Significantly higher efficiency, greater power output (typically 3X or more) and an implied requirement for local or global feedback to linearize the switching transition in the output devices.

@lynn_olson I think most people haven't thought this bit through. If there is a switching transition in the output devices (producing crossover distortion) then the amp is actually biased class C. 

Class B is defined as exactly 1/2 of the audio waveform. If its more than that the output device is biased AB, if less than that its class C. Class B has really only been theoretical on this account until perhaps recently when microcontrollers could be used to actually really get the output device(s) to do exactly 50% of the waveform. 

EV used to sell amps back in the 1950s they claimed were class B, such as the A20 or A30. Indeed they made double the power you would expect out of a pair of the same power tubes in class A and the tubes ran cool. They had no zero crossing artifact at any power level you could measure (I have an A20 so I've put it through its paces)...

This all says they were really very lightly biased AB amplifiers. AB amps won't have a zero crossing artifact unless there is a design flaw (usually a problem in the driver circuit). Feedback won't fix a zero crossing artifact since there is no loop gain at the zero crossing if the outputs are in cutoff. So if the amp is AB there's no worries since there's loop gain. 

Put simply, most of the time when people talk about a zero crossing artifact such as 'switching transition' they are talking about an amp that is biased class C. Douglas Self wrote about an amp he designed called the 'blameless amplifier', which is an example of a class C push-pull amp, although he claimed it was class B. But if you really think about it, you know the class B in the real world can't exist without computer control. 

Try Accuphase A36, A48, A75 or A80 depending on your need.  They run cooler than Pass Labs counterparts.

Ralph, I hate to disagree, but a pure Class B amp (like the Quad 405), switches from the upper set of transistors to the lower set with no region where both are operating. Class AB has an intermediate region where both are operating.

In a typical Class AB amp, whether tube or transistor, there are three operating regions: the plus direction, which activates the upper output transistors (or tubes), the middle zero-crossing region, which activates all devices at once, and a minus region, where only the lower devices are operating.

The size of the middle, zero-crossing region is at the discretion of the designer. If this middle region is so large that the B regions are never activated, it becomes a Class A amplifier (by default).

The Quad 405 had no A region, and relied on the feedforward system to supply current and voltage for +/- 0.7V region where all output transistors were turned off. As a result, it ran quite cold, but if you had a good enough distortion analyzer, you could see the switching region along with a spray of harmonics.

Class C is reserved for radio frequency transmitters ONLY. This has massive distortion since not all of the waveform is amplified ... there’s holes in it. It doesn’t matter in RF applications because tuned circuits filter out all of the harmonics, and Class C is more efficient than Class B or AB.

Class D is a switching amplifier, akin to a switching power supply. Pulse-width modulation converts the incoming analog signal into PWM, which is applied to very high speed switching transistors. A lowpass filter at the output removes most, but not all, of the ultrasonic grunge. It is normal to apply substantial feedback to linearize the PWM modulator and correct for small timing errors in the switching devices. (In PWM, timing errors translate into distortion when lowpass filtered.)

Here's a succinct explanation on Wikipedia:

Amplifier modes of operation

Nice to see mention of the Classe DR3-VHC.  IIRC they only made 133 of them and I have 3, a pair running bridged and a single running in stereo in another system.  The bridged VHC puts out 500 watts into a 1 ohm load all day long.  I bought mine from a system using Apogee Scintilla speakers - there were very few amps that could run those into 1 ohm.  Great amps

Valvet Audio also makes class A SS amps that don’t get hot. They sound wonderful! 

After I tasted class A years ago I tried some class D to see if they could compete. Class A for me until I am forced into a different situation. Never say never, but as others have stated, so many Class A amps today don’t really get excessively hot so they are fully enjoyable. 

Classé DR3-VHC are on my bucket list, as are Aleph 0.

Class A amplification is like Porsche. Not for everybody but always the standard of comparison. 

Love my Pass Labs XA25. First time with pure class A. Would really take something special to go back to A/B. Class D not for me. Only drawback is power consumption. Like the analogy with the Porsche. Luckily not the same price point for my Pass ;-)

An A/B class amp drives initially in class A, then at higher outputs switches to class B, if I remember correctly.

 My 100 wpc stereo AB power amp operates in class A up to 10 watts then the peaks cross into class B, peaking at roughly 100 watts. So the top 10dB uses class B.

 So truthfully, your AB amp will operate (admittedly, on listening volume and speaker efficiency) 99% of the time in class A. I am using 10watts where as a full class A uses 100 watts. Is the higher power bill worth that 10% for a 100% class A amp?