Class A into Class AB

To me the first few watts of class A are the most important. That is where 85%+ of your listening will exist. Only on big crescendos and heavy bass lines will you require more watts. The extra wattage is for headroom when needed. IMO, class A watts are sweet, natural and musical. I could expand further but that would take several paragraphs and I am sure other members will have plenty to say more eloquently than I. I know that I prefer Class A and I own the CODA CSX with 20 watts of class A. 330wpc @8 ohm/660 @4ohm. I real stunner in silver!!!

Class A gets expensive as you go up in watts. Big power supplies and heat sinks because they are biased to run at full power when idle.  

@Tom6897 is correct on the first few watts. I own the Luxman 590AXII, it was a tough decision to go with pure class A over their 509 with A-AB with more headroom. I do not believe it's hype or marketing. For me, I decided I didn't need more then the 30 watts into 8 ohms or 45 into 4 ohms. I just don't play my music that loud anymore and with 30 watts, I can get well past 90db if I really need too.  I have found it to be plenty of power, but I do still wonder if I could have heard the extra headroom in an AB amp - or perhaps heard the amp when it switches from A to AB (I've heard that some can hear it, some say BS). Just giving you my experience - I doubt I'll ever go back to D amps which I have owned many times.

A for the first few and a/b after that saves electricity, heat, and money in your pocket.  You want some A to start with for the improved sound.
So no it is not a scam or marketing hype but actually giving people what they want or should want.

My (limited) understanding is that class B designates a push/pull configuration with each device (tube, transistor) handling one half cycle. During the transition between devices there is distortion. Class A is always on, drawing the same amount of power regardless of the input signal. Biasing the devices for class A/B helps reduce the transition distortion because there is no longer an abrupt transition between devices. Both devices operate in the transitional region which varies widely between designs. 

@deadhead1000
The 590s are also A/AB. Goes up to approx 90W in AB, so there's your headroom.Fantastic amp, I have the AX, but not just class A
On the other hand, this probably shows that it's difficult to notice it moving from A to A/B

Why you just picking on integrates?

tom68971,405 posts10-09-2021 1:14amTo me the first few watts of class A are the most important. That is where 85%+ of your listening will exist

~~~~~~~~~~~~~~~~
La Creame de la creame.
Great Britain calls it  Double  Cream*  When fresh cows milk settles, the  top layer of the cream layer. = Double cream. 

With 92 db sens wide band, only 5% of the Defy's 100 watts are needeed.
Class A, class A/B is  not important. 
At 5% , Class is irrelevant.
I listen at very moderate SPL levels, maybe 75 db tops.
Even though low SPL and very near field, I still want higher sens speakers. 
Doing it all over again, I would  have a  much smaller amplifier.  with exact same results. 
IMHO 40 true watts,,make that ~~30~~~ true watts is  really more than enough power. 

What is the goal of a designer who makes intergrated amps that have class A for x amount of watts before it goes into class AB?

to provide a balance between purity of sound for most of the listening experience, versus heat, cost (of the unit and energy use), volume headroom, weight/size of the unit

Are there any examples of this being implemented well?

yes there are many

My stereo experience began during the watt wars in the late 70’s and early 80s.  30 to 50 watts with horn midrange and 12 inch woofers made wood filling sound and no damage to speakers during peaks.  Watts became cheaper d speaker designers were free to experiment with smaller woofers and inefficient crossovers.  I had an power meter from realistic and measure the output from from a 100 wpc nakamichi stasis amplifier into my Polk sda 2 speakers.  The meter had a high and low setting 0 to 1 watt and 1 to 100. Even in a large living room most of the listening was under 1 watt and momentarily reached 5 during peak symphony or rock drum/bass combinations. 

I use a Vincent Audio pre power SA 31 MK / SP 331 MK, first 10 watts are Class A. Calculations imply that would be 99% plus of my listening time. 

Why are you not using Class D?

I found the real sweet spot.  I bought a 1970s vintage Yamaha CA-800.  A very nice class AB 55 or 60w into 8ohms ...with a wonderful *twist* above & beyond its classic look.

It has an operating mode switch whose purpose is to keep the amp operating solely in Class A mode (rated at 10w in Class A, I think)
-or- to operate normally in AB behavior and the stated power rating.  

Now, be -very- jealous!!  ;-)
I am not aware how many Yammie models had that nor do I know over what time period such a control was available.  Whether other manufacturers of that or any other era have offered such a control--I don't know...
Warren

It is mostly marketing jumbo jumbo.
Any biased AB designed will be biased, and the amount is either 0.6V or more than 0,6V (like 1.2V).
So a 1.2V bias design always runs as class A under 1.2v.
So yeah it it marketing.

If it was a Class-A on the tweeters, and an AB on the MR and a class B on the woofers, then that is a different beast of a thing.

It is mostly marketing jumbo jumbo.
Any biased AB designed will be biased, and the amount is either 0.6V or more than 0,6V (like 1.2V).
So a 1.2V bias design always runs as class A under 1.2v.
So yeah it it marketing.

If it was a Class-A on the tweeters, and an AB on the MR and a class B on the woofers, then that is a different beast of a thing.

Just starting to use Class D since it’s less heat generation than A etc 
I live in So Fl!

Have used PS AUDIO and Peachtree
v happy esp with z Peachtree 150

Class A/AB and class AB are the same thing. At lower powers the amp is class A and at higher power class B. How much class A depends on the amount of bias and can range from less that a watt to lots of watts which is rare.

But even a low efficiency speaker say 82 dB plays a continuous 82 dB with a watt and that's fairly loud so an amp with just 1 watt class A goes out of class A only on peaks which last only a very short time. So class AB amps are in class A most of the time.

Most amps even those costing 6 figures are class AB and well designed class AB amps sound awfully good these days and have more head room than pure(never go into class AB) class A amps which are extremely rare except for single ended amps which must be class A and single ended amps are very low power.

By the way almost all push/pull class A amps go into AB at very high powers especially into low impedance loads. For instance Class A Pass amps go into AB. But they only give you the class A rating in their ads. They produce twice as much power usually total but it's AB then. The only
 push/pull true class A amp I know of was he old Mark Levinson ML2 which was 25 watts class A into 8 ohms and still class A at 100 watts into 2 ohms.

Then there's the sliding bias amps which could be called class A but some argue they aren't true class A. I'm not going into that discussion.

Hello, 
It is not marketing hype. From what I understand the class A/B switches on and off. This lets you have more watts with less amps. It is more efficient and therefore runs way cooler. Most designers bring in the class A just above or below that point where the switching is so you have better sound and don’t notice the gap. So at normal or regular listening levels you are in Class A. When you go higher or the music becomes more dynamic the class A/B takes over. 

just to set folks straight that may not be properly informed

https://www.audioholics.com/audio-amplifier/amplifier-classes

If you play in class A at 8 watt with high efficiently  speakers ( > 96 db) than , in your listening room, the music is playing  loud . You do have a beautiful high-mid-low . If you measure the volume in your listening room,you will be around 4-6 watts : many thinks, the amp performs much more. ; so , most of the time, you play in class A, and I’m totally agree with what the previous ones say about class A properties: heat……

Since amplifiers typically operate at lower output levels than their power ratings, the higher the class A wattage rating, the more it operates in class A, so there is or can be an advantage for higher class A ratings in an otherwise class A/B amp.
I have designed and constructed a number of power amplifiers, including one capable of pure class A operation at 100 watts into 8 ohm loads and one capable of class A operation up to about 20 watts into 8 ohms although it can output 120 watts at 0,1% THD.
Both amps sound fine.  However, it is nice to know that one can provide class A operation at 100 watts.
The price is that the power dissipation in the output stage of a class A amplifier is twice its power rating.  The 100-watt class A amp therefore dissipates 200 watts under no-signal condition, so heat-sinking is critical.  For that reason, that amp was constructed as two monoblocks in separate enclosures for stereo use.  The two get quite hot, but no failures in over twenty years of operation does mean it is practical to build pure class A amps capable of respectable output wattage.

That's the definition of a class AB amp.  So what's the beef?

I never hear the word ARCAM in this discussion group?  ARCAM makes a ARCAM 30 that is Class G.  It costs double the price of their ARCAM 20 a class AB amp.  However, when I heard class G, I really felt it sound better.  Not sure why.  It had plenty of power and headroom.  I am still thinking about owning one.  

One thing about a Class G is it runs cooler than a Class A which can get really hot and it is not suited for an enclosed cabinet.

One thing about a Class G is it runs cooler than a Class A which can get really hot and it is not suited for an enclosed cabinet.

most members are aware that class a amps run hot and need to be out in the open.

another agreement with @tom6897. **Pure** class A is tons of money, heat for what amounts to very little benefit. High bias Class AB works great.  There are way better places to spend money and get more sound improvement.

And i design these things.
The idea of subtle nuance while the amp is running at 100% of power is a contradiction.  The room is shaking.

I find the Class A amps that I have owned smoother sounding than AB amp that I have owned. The CODA CSiB is a good integrated amp. I had Version 1 with the most Class A watts. I still own the KRELL K-300i integrated which does not put out a lot of heat and has the first 90 watts in Class A. I liked it more than the CODA CSB so Is sold the CSiB and kept the KRELL.

I also have the CDDA 07x and CODA #8 (Version 1). I like that combo more than the CSiB. Last week I heard the CODA #16 with the CODA 07x and it was easily better sounding than my #8. The #16 has the first 100 watts in Class A. It sounded smoother than the #8 and with more clarity. The CODA #16 was not that hot. Maybe I needed to play it for a few hours at loud volumes?

I have also had 3 Class D amps recently. Which were enjoyable but sold mainly because I liked the CODA gear a bit more.

@larry5729 

maybe arcam has made some sweet sounding amps in their history, but after owning 3-4 arcams over the years, for various purposes, i have yet to experience one

The Luxman L-509X is biased to be pure Class A for the first 6 watts.

I've got mine paired to Audio Note AN-K SPx/SE at 90db efficiency.

I do practically all of my listening in Class A - if you believe those seductive dancing meters :-)

I do practically all of my listening in Class A - if you believe those seductive dancing meters :-)

I believe you and the others, including myself, that in an RMS sense… it is mostly Class-A.

Just the crest factor of a lot of music can be ~13dB. So that often jumps the peaks up to Class-AB.
Maybe at 60-65dB it is under/within Class-A.
But at 75-80dB those peaks will be above the meager level where the bias disappears it being qualified as “Class-A like” operation...”
And it has historically been in the louder sections of music where I have heard the grainy’ness, so maybe that was cross over distortion from Class-AB?

Pure Class A if you please...

6 watts is quite a lot of class A power.  Given that most decently recorded music has a peak:average ratio of ~ 10 or more, that means that peaks would be 60 watts if you were, on average running in class A.

And 6W is a lot of power! (surprisingly). As a designer i put a lot of experimental (read that: could blow up) stuff in my system with very expensive speakers.  So i have fused adapters pretty much all the time.  I use 1A fuses. Which means that they blow > 8W. They never blow.

that in an RMS sense… it is mostly Class-A.

I think you mean in an **average** sense. RMS has to do with how we measure a wave:  peak, average, or "area under the curve" (root mean square or RMS).  It is quite different.  For a sine wave RMS = average. For complex waveforms you need to integrate to get the area.  Eek! calculus!


But your point, if i infer right, remains valid.

The Threshold S550e amp from the early 90's was rated at 250 WPC.
This stasis design had optical bias circuitry and the bias was set at 100mV.
Threshold claimed that it would run up to 20% of it's rated power in class A (that's 50 watts!!)

My NAK PA-7A MKII is also a stasis design but without the optical bias circuit of the S550e of the same era.

Bias specs for the NAK is 40mV but I run it at 50mV. It draws around 200 watts at idle. It's rated at 225 WPC.

My guesstimate is that it runs in Class A for the first 10-12 watts.

Geez i fell like a detective, and with that data inspector Clouseau to be specific.....
per the threshold - complete the math!!  100mV across what? What's the derived current (which is what matters)?  Across the emitter resistors, which are what value? Without that you don't know the current.  Let's assume 1 ohm.  We shall assume per device, but number of parallel devices unspecified.  If nelson claimed it was A to 50 watts, that's 20V/8ohms or 2.5A; which implies 25 parallel NPN and 25 more parallel PNPs per channel -- minimum.  Some number there does not add up.

Why don't you ask NP on diyAudio.

i don't really care, just trying to figure out what you were posting about and don't have the data.  was not clear what your point was....

Re: the Threshold 500’s.  Claimed 20 output devices per channel, for 250 Watts per channel into 8 Ohms with about 20% of that being Class A,  the Class AB power output could steadily double down into 4 Ohms, but while doing so the Class A output would halve, the amp was said to be capable of doubling it’s rated steady state output for up to a couple of minutes.  Nelson Pass might have been a bit generous to himself when it came to how he defined Class A. Still, IMHO impressive.

My Parasound JC1's have a high bias mode which provides 25W of Class-A before switching to A/B, vs 10W in low bias mode.  It's clearly an audible improvement which I use when doing serious listening.  Not marketing fluff in my experience with the JC1's, but I'm sure some implement this better than others like all things.

@itsjustme FWIW, 0.5 Ohms is a good assumption for an emitter resistor in an output section. 1 Ohm is not!

@itsjustme...   was not clear what your point was....

The point is the name of the thread is...... Class A into Class AB

1 ohm is not uncommon with many multiple parallel devices (which is very likely there) to ensure load sharing and some additional linearity.  You may find it high, i really don't.  Seen a bunch.

Since the OP posed the question, with regard to integrateds going Class A to AB, "Are there any examples of this being implemented well?" I would submit the example of Nelson Pass's INT-60. According to Pass Labs documentation, it remains in Class A until 30 watts, then transitions to AB. (The unit puts out 60 watts into 8 ohms.) In theory, the blue meter at the front center will move past the 12 o'clock position to tell the user that it's crossed into AB operation. In practice however, in the three years I've owned the INT-60, it has never, ever done so. This includes a few occasions when my friends and I were overserved with "listening fluid" and briefly turned the rig up to the "ridiculously loud" level. It never got close to passing 12 o'clock.

In other words, if the meter is to be believed, for all practical purposes, the unit never leaves Class A. Incidentally, Pass describes the INT-60 as Class AB, not A/AB. As you would expect, it runs hot, but not crazy hot. What this all means, I don't really know, but I do know that it's a phenomenally sweet-sounding unit which I have enjoyed enormously.

 "...Implemented well?" I'd say, "yes."  

The meters on home audio gear are almost never calibrated and more often than not mislead rather than inform.

The meters on home audio gear are almost never calibrated and more often than not mislead rather than inform

How coils they be accurate when they often report < 1W ?

@unsound  As a general rule, I wouldn't disagree with your statement in the least. But in this particular instance, we're talking about Nelson Pass, who is, to say the least, not known for misleading.

@pjcoughter, I believe the meters were intended to entertain not mislead. I would hazard a guess that if asked, Nelson Pass would readily admit as much.

Touché, @unsound.

When I first put a voltmeter on speaker terminals I was “shocked” at how low the voltage was… and that was with 8 ohm speakers.

By the time you get to 4-5v it is almost shaking the house.
A meter is a pretty easy thing to make, and they have been doing those for around century.