In the same line of amps I think it's pretty safe to say that the 200W is "more powerful." Sometimes the watt rating is so misleading as to not mean much.
The class just tells you how they are biased. Some folks think class A sounds better. Class A is almost always less powerful because current is running all the time. If a circuit has a chance to rest(cool down) during part of the cycle it can take more current during the time it is on-more power because two (or more) components take turns handling the signal instead of dealing with it all of the time. In AB the current is running more than half but not the entire cycle like in class A.
Class A will not give you more "power." Nor,imho, would an amp drive a particular speaker better just because it is in class A.
Some think it sounds better.
I agree with part of what Clueless said. I disagree with the other part of what Clueless said. : ) Sean
Sean, for the record, you are making a habit of crashing threads.
Tabu, hell if I know, but with my Pass X150 running into AB after only 15 watts, I never could tell the difference. With my Scinnies, the X600 does that after 150 watts, and I still can't tell the difference.
I'd pick whichever is stable into a 1 ohm load. Wattages given are probably 8 ohms.
An unfair (pricewise) comparison is my Plinius SA100 MKIII power amp has 100 watts class A and my Plinius 8200 MKII integrated has 175 watts AB and the SA 100 MKII clearly has more OOMPHHH and control without breaking up. The 8200 might go a little louder but gets thinner and washed out in a typical way. This is when I was running Maggie 1.6s which like all the current you can throw their way.
Clueless- Please do not take this as a personal attack. However, Believe I have read that Class A amps provide a greater percieved scence of power. I could be mistaken, but my understanding is Class A amps provide power the entire cycle. Thus, they maintain better "control" over the speakers.
Not taken that way at all.
My response above was very limited to amps in the "same line."
Kind of "all other things being equal" response.
Class A amps are often more expensive amps and have many things (designwise) going for them besides the typical W rating that is often taken over a very limited range. An amp has to have a lot going for it to respond across the frequency range and control a speaker.
All audio amps provide power the entire cycle. If they didn't you would have real distortion. With class A every output element(I really just deal with tubes) is biased so it is on all the time. With AB they do not and the output elements have to pass off the signal and this can cause distortion.
I agree with you re the "perceived sound." IMHO It is not a matter of just a wattage rating though. Many things are involved.
Control of a speaker is a good example and a separate issue.
A complex one too.
Hey Sean tell us what you think!!!
I always thought that the benefit of Class A over Class AB was that, apart from the build factor, was the elimination of distortions due to the switching from Class A to Class B when you reach the limits of Class A in any particular design. Did I miss something?
Clueless has got a right clue.
Watts are all created equal: class A, AB, tube SS, digital etc...
Power ratings can or can't be precice and/or honest depending on manufacturer.
There are quite a few power ratings that have to characterize an amplifier and part of them is partially derived of power supply capabilities along with output devices that are critically calculated for the large signal calculation and class of operation.
From what I have gleaned, Class A can do without feedback, and that is a very good thing. Direct coupling is a good thing too.
There are amp builders who accomplish both.
One point missed: a 100 watt 'real' class A amp would use enough electricity to power your whole house, just idling. And it would serve as a great winter heater too. (the 'real' because even very good class A amps change over to AB at some point in the power range)
My little baby class A amp a Forte' 4 at 50 watts channel uses $10 worth of juice a month when it was connected to my Infinities... ,when connected to my Maggies the same left on all the time amp uses only $5 worth of electricity... SEAN TELL ME WHY!!!!)
did you check the price per kilowatt-hour?
1.Direct coupling can even be done with digital amplifiers between the stages as well as at the speaker binding posts.
It has nothing to do with class of operation.
2.Any amp with no feedback will oscillate. A feedback is a-must in input and driving stages.
3.Class A allows to minimize the feedback at the output stage but presence is still helpfull and very often even neccessary.
Eliz: I agree with some PP - SETS stay in class A.(least we confuse someone)
Muralman: yes, class A can do with less or no global feedback (local is another story) but that is a different issue than we started which was if a Class A nominal 100 W amp devivers more power than a nominal 200W AB because it is class A.
I'm pretty much a SET person these days but I think feedback has gotten a bad rap. 15-20 years ago lots of poor designs used too much feedback in an attempt to compensate for poor design. Feedback took in on the chin. I'm not crazy about it but I think it's to generally scorned sometime.
I read Plinius likes class A because the load on the power supply does not fluctuate
OK guys, here is an answer from an EE perspective:
Like Maranketz wrote: all watts are created equal 'cuz it is a measure of power. Nothing hokey here. Just plain simple math: power = current squared * resistance.
Class A power amps have the least distortion thus the best sound quality 'cuz the output stage devices are biased so that they are always on. The maximum output current deliverable by the amp ALWAYS flows thru the output stage when the amp is powered on whether there is a load or not. If there is no load, the output current flows from the source transistor/tube to the sink transistor/tube into ground & is dissipated as heat. When there is a load then some/most/all (depending on volume level setting) goes to the load/speaker & less is dissipated as heat. That is why class-A amps run cooler when hooked up to a load/speaker! Theoretical max. efficiency for a class-A amp is 25%. "Elizabeth": your Forte amp would dissipate 200W while idling. That is not a lot, as you will agree, & I'm sure you'll also agree that 200W won't light up your entire house. It will be a diff. matter with some of Pass' class A amps like the XA-200, which would dissipate 800W while idling!
To answer "Tabu's" question: the answer is not clear cut 'cuz you have not told us which power amp can provide more current. It's all about how much current a power amp can dump into the speaker load. The 100W class-A can provide 3.53A max. of steady-state current. The 200W class-AB can provide 5A max. of steady state current. All this is well & good. The thing is that the music signal is NOT steady-state! It is a dynamically moving signal. So, if the power amp is to be true to the music then it must
* track the music signal - slew rate of amp
* provide sufficient current while slewing
The amt. of current providable is a function of the power supply & power supply capacitors. Why do think that many huge amps (take Pass for eg. weigh a ton?) It's that honking xformer & those massive power supply caps! large xformers are able to draw large amounts of AC current QUICKLY, which is converted to DC & used to charge up the power supply capacitors, which act as charge/current reservoirs. Any time there is transient (kick drum/bass riff, etc) the amps sends out a burst of current (taken from the caps) into the speaker. Only if sufficient current flows in the speaker voice coil can the cone driver create pistonic motion to create sound. Low current output from amp => weak cone driver motion => loss of sound.
A good eg. of a powerful class-A amp is the Clayton M-100. It puts out only 100W but it can supply 200 Amps of current! I believe that this amp can slew rapidly too using some hi-power Motorola BJTs. This amp has a lot of oomph & can drive a variety of speakers. Hell, one could weld w/ this power amp!
So, without further info, I'd be hard pressed to say which would be better. The 100W class-A might just be enough IF it has sufficient current drive. Listen to both, if you can, before deciding. From a pure distortion perspective (forgetting everything else), the class-A will always sound better since the output devices are always on & there is hardly any xover distortion compared to a class-AB amp. There are several class-AB amps today that are heavily biased towards class-A so they *almost* have a class-A sound. These are, of course, better than class-AB amps weakly biased towards class-A. Pass' X series amps are class-A for the 1st 30% & then class-AB. However, if you buy a X250, for eg, you will get the 1st 75W in class-A, which is all you really need for 90-95dB SPL listening levels. It is also one reason the amp is expensive - you are *practically* getting a class-A amp. The heat sinks on the X250 also tell that story.
"Elizabeth" if I had to guess why your elect. bill is higher w/ the Infinity I would guess that the Infinity's xover is more complex & power hungry than the Maggie's. I know that if the speaker designer doesn't use the "correct" Zobel network on the woofer drivers, the woofers present a varying impedance over freq. i.e. they are not a constant 4 Ohms or 6 Ohms or 8 Ohms, etc. This means that the amp has to source current over a varying impedance. Using the equation: power = current squared * resistance, you can see if resistance varies, power varies in direct proportion. This is, of course, DC power. But where does the DC power come from? From the AC outlet, which is AC-DC converted & stored in the capacitors. If the capacitors are drained quicker when the woofers drop to a low impedance/resistance, larger AC current has to be drawn from the outlet to replenish the capacitor charge. This will affect your elect. bill. In comparison, the xover of the Maggies appears to be better designed in that it presents a more even keel impedance vs. freq.
Hope that this helps some. FWIW. IMHO. YMMV.
thank you all it was very instructive,
it is too bad that the good treads don't last long enough to prolong the discussion
I have read in Pass Labs white papers, the Pass X and XA amps only utilize feedback locally to assist Supersymmetry.
The X600 runs class A to 150watts. The sound never thins out or is audibly distorted A or AB.
Hey Bombawalla, excellent critique.