Class "A" watts

Larry Robbins · Post by **Larry Robbins** » 4 Mar 2004 7:46 pm

OK Ill" show how dumb I am......
When I read ads for certian amps I see the
term"class A" Watts when describing how much power an amp has.What the heck dose this mean?...Thanks

R. E. Klaus · Post by **R. E. Klaus** » 4 Mar 2004 10:12 pm

Ok, now you've done it. I'm on my soapbox. Having spent the last 30+ years in electronics, many of them in audio service, and a couple teaching, I am rather picky about correct usage of electronic terms.
There is no such thing as "Class A watts". "Class A" refers to the type of amplifier circuit (more accurately, the way the circuit is baised...but that is another topic) that is used to provide enough current to the load, in this case a speaker, to produce the desired result, in this case sound. A "Class A" amplifier is considered to be the cleanest (distortion wise) type of power amplifier. Unfortunatly it is very inefficient (about 50%).. wastes as much or more power in heat than it sends to the load. Another words a 200 watt output would require at least 400 watts to be drawn from your electrical outlet. Most power amplifiers stages in the amps that we use are "class AB" type. They are much more efficient (typically about 80%) but not as pure distortion wise. There are several other classes as well but not so commonly used.
As for the "Watt", a Watt is a Watt is a Watt. The Watt is a unit of power measurement. The only true Watt is the one that say "Watts RMS." It is measured by using RMS Voltage and RMS current or calculated using load impedance, RMS Voltage, and/or RMS Current. Sorry about this a little long but it is just not simple to simplify.
R.E.[This message was edited by R. E. Klaus on 04 March 2004 at 10:20 PM.]

Earnest Bovine · Post by **Earnest Bovine** » 4 Mar 2004 11:07 pm

Carvin Watts are much smaller than other Watts.

Larry Robbins · Post by **Larry Robbins** » 5 Mar 2004 2:42 am

Thanks for the reply.Then I take it as a
misused term/poor marketing ploy.I see the term used on a lot of those retro looking amps that are on the market.You know,those little things with the 10" speaker and
15-30watts of "classA"power that they want a small fortune for.thanks again for clearing this up.Im sure Ill have morer dumb questions later.

David L. Donald · Post by **David L. Donald** » 5 Mar 2004 4:21 am

Class A indicates that a single tube or transistor is passing the whole sine wave signal without cliping or squaring off the top of the waveform, in one stage.

In a power amp this is an energy hog, but again as above, the cleanest signal path.

The other classes B AB and C, in different ways, are splitting the top half of the wave to one tube or transistor, and the bottom half to another and then passing them on recombined in parrallel.

More gain for less energy tax at output.

But this gives rise to some distortions of the waveform and small time delays of the signal, due to inherant differences in individual components.

In a preamp or prossesing unit like a compressor or EQ , Class A is much prefered because it is cleanest.

In a power amp it is nice, but expensive.
Hope this helps

John McGann · Post by **John McGann** » 5 Mar 2004 6:59 am

Larry, before you dismiss the low powered class A amps as mere marketing, play through one. They may not be the best amps for steel, but for underarm guitar, they are very cool. I have a Matchless SC-30 and a bunch of great old Fenders for guitar. I love them all, but the Matchless has a unique personality, like a very hi-fi Vox AC-30. A great, classic sound. Luckily, I got mine on the cheap when they first came out in '92, because I was friends with a distributor.

David Doggett · Post by **David Doggett** » 5 Mar 2004 7:07 am

So while what the advertisers are doing is a little confusing, it is not completely bogus. Although a watt is a watt, what they are trying to say in a hip abbreviated way is that these watts, being from a Class A amp, watt-per-watt are cleaner.

To continue in a similar vein of electronics challenged questioning, what's the deal with "tube watts" versu "solid state watts?" I always thought a watt is a watt, but tube freaks (which I have reluctantly become myself) always assure me that a tube amp is louder than a ss amp of the same or even higher watt rms rating. I doubted that at first, but have had to admitt that there is something to this, or it is a very powerful illusion. My 100 watt Fender tube amps sound louder than my 100 watt ss amp. And I play with a 6-stringer whose Gretsch 6120 through a supposedly 15 watt '50s tweed Deluxe can blow the walls out of a rock club and sounds way more than half as loud as my 100 watt ss state amp. What's this all about?

C Dixon · Post by **C Dixon** » 5 Mar 2004 7:30 am

David,

"louder" is a nebulous and subjective term. The following is why tube amps are perceived louder than solid state amps by some players; and many ppl listening to music played through them.

A tube operates in a vacuum, thus "transient time" is instant for all practical purposes. A solid state device is just what its name implies; it is made of solid material. Thus transient time is slower.

So what has this got to do with loudness?

OK,

Music, (unlike power lines and many devices consuming power) is not constant. IE, you may play a note softly, then instantly play very hard or anywhere in between. This means that an amplifier must go from soft to loud (and vice versa) instantaneously, if it is to reproduce exactly what was fed into it.

This physical attribute of any amplifier has been labeled "dynamic range".

Now the human ear will just about always perceive an amplifier to be "louder" IF its dynamic range is HIGHER than another. So that brings us back to the physical characteristics of tubes operating in a vacuum, versus transistors working thru a solid. Or in other words,

"A 100 watt tube amps sounds louder than a 300 watt SS amp." This is because the SS amp is "slower" to respond to change than a tube amp because of dynamic range.

When SS amps first hit the market their dynamic range was so bad, that litterally, a 500 watt SS sounded less loud than a 50 watt tube amp, to most listening to music played thru it.

But as R. E. Klaus so poignantly said, "a watt is a watt is a watt!" The SS state amp above is 10 times more powerful than the 50 watt amp. NO question about. Any audio engineer (worth his salt) in the world would attest to this.

But to the listener (BECAUSE of dynamic range) the tube amp is perceived to be louder than the SS amp.

Fortunately, they have come a very long way in SS amps over the last 45 yrs. And today, SS amps are coming very close to the dynamic range of tubes. Not 100% of course; but soooo very close that many cannot hear the difference in same wattage applications.

The class A ads have truth in them as several posters have intimated. Also, left out of the ads is they consume more power versus power output than tubes operated class B, AB1 or AB2. (No audio tube ever operates in class C since the distortion would be intolerable.)

In a practical sense, the following is what happens:

1. Class A means the tube is operated 100% in the linear portion of its charateristic curve.

2. Class AB1 means the tube is barely conducting any current UNLESS music is being amplified, then it amplifies only HALF of its input. Its sister tube takes care of the other HALF.

3. Class AB2 is identical to AB1, except it consumes even less current when no music is being amplified.

Both class AB1 and AB2 require at least 2 tubes operating in a push/pull setup. As far as distortion, (harmonic or intermodulation) Class A has the least, then class AB1, then class AB2.

(NOTE: Class B is rarely ever used in audio amps because similar to C, its distortion is intolerable.)

Guitar amplifiers have used any one of the above three in a myriad of applications since the advent of amplifiers.

Remember, there is always trade offs. In a word,

"there is no free lunch"

UNLESS.... we are talking about Jesus, then ALL his gifts ARE 100% free,

carl[This message was edited by C Dixon on 05 March 2004 at 07:47 AM.]

David L. Donald · Post by **David L. Donald** » 5 Mar 2004 8:23 am

One reason the Matchles sounds "classic" is because a number of the OLD amps were class A.

Another reason besides transient responce differences in tube amp vs transistor is that when a 100w tube amp hits 100w peaks and starts to distort the waveform, it is doing it in a "sweeter" type of distortion.

Sort of a rounding of the peaks rather than a flattening of them.
Imagine your hand is the waveform...
punch a waterbed,
and then punch a wall....
which does the least amount of damage abruptly to your waveform/hand.

~Eventually you will hit the bottom of the bed, but you have plenty or warning,
and your hand slows down progressively before it gets to the flattening bottom.
Just an analogy.

So as a marketing phrase
40 Class A Tube watts means a sweet sounding amp, that is very clean till it goes into distortion.

60 Class AB2 solidstate watts means a very efficiant amp that has a brickwall maximum of volume available. And when it goes, it goes over harshly.

The smaller tube amp actually should have an apparently louder sound.

Humans hear aproximately 1.5 db difference in sound presure levels as a change in level.
Less that that and we don't think the level has changed.

Now doubling the apparent sound levels is not done by simply doubling the wattage.

50w to 100w I believe will give only a 3db greater level. Noticable, but not doubled.
Well yes and no, it is I think a logrythmic scale, so in a technical sense it is doubled , but in an apparent sense no.

400w will likely double the sound of 100 watts.
Sorry I forget the exact power to measurable Db volume doubling ratio. So this figure could be off, but you get the idea.

So that 40 watt Class A tube amp will smoke the drawers of that 60w transistor amp, and sound sweeter doing it.

But this also explains why there are guys playing with 400-500 transistor amps,
and others playing the same gigs with 100w tube amps.[This message was edited by David L. Donald on 05 March 2004 at 08:28 AM.]

Ray Minich · Post by **Ray Minich** » 5 Mar 2004 9:19 am

Nomenclature will get ya everytime. You gotta know the secrets behind it.

I always got a chuckle out of the dinky little speakers that were rated 100 Watts PIP. Turns out PIP is Peak Impulse Power, and thats the power transfer that occurs during the several milliseconds that elapses just before the speaker cone gets blown across the room.

David L. Donald · Post by **David L. Donald** » 7 Mar 2004 2:11 am

Ray I know that one...
Impulse Power ain't that what moves the Starship Enterprise?

I one was once mixing on another large sound system than my own.
Well one of their 400w a side power amps was on the way out, and then Boston Edison
and a drunk trucker gave it a push with an unexpected re-set spike.

The amp red lined ; PIP +2 and sent two 15" speaker cones and it's self into the hereafter.
But it also sent those 2 nice shiney metal cone centers through the wind screens,
and one took out a beer bottle 5 feet away on a table.

The owner of the system tried to dock me the cost of the amp and speakers, till his band mate confirmed what I had pointed out;
his 6000 watt system wasn't going to be killed with only 1 singer and 1 acoustic guitar
playing at the time, the band wasn't even playing on the song...

And the report of a telephone pole down 3 blocks away,
and the edison system grid resetting and surging.

The electronics tech who looked at the amp reported it was not a simple overload. He noted the powersupply no longer existed.

Still it was an impressive display of short term PIP!
And the bar gave the kid a replacement beer.[This message was edited by David L. Donald on 07 March 2004 at 02:14 AM.]

Gino Iorfida · Post by **Gino Iorfida** » 7 Mar 2004 2:44 pm

... and now you are all going to hate me, but I'm sure Ken Fox and maybe a few others will pipe in here to cover my back.

A __LOT__ of the amps that are touted as being 'Class A' are really not class A in the least, but rather class AB, but biased rather hot. The famous Vox AC30 was NEVER a TRUELY Class A power amp design. For a push pull style amplifier to be truely class a, would requre massive massive transformers, and owuld be simply put, too expensive for musical inst4ument amplifiers. NOW by the true definition of Class A, all single ended amplifires ARE by nature class A-- a classic example owuld be the Fender Champ, a more modern example would be the THD univalve-- in other words, if there are more than one pwer tube in the amp, 99 out of 100 cases it wil be a class AB amplifier (at least when talking musical instrument amps-- hifi may be a different story altogether, although, debatably, some fo the best sounding hifi amps were actuall y not class a, class ab but rather true class B power!) A majority of the time when somene claims an amp (over 10 watts when talking tube,guitar amps) IS class AB.

Stephen Gambrell · Post by **Stephen Gambrell** » 7 Mar 2004 8:54 pm

WELL, Gino, I've read this stuff, too, and I don't see how an amp COULD run Class A, if power tubes are in pairs, or quads.
I think a lot of people are making a TON of money, selling low power, hand-made amps, for big bucks. Especially when an old Champ can still be had for WAY less than 1000.00!
Ken???

Dave Boothroyd · Post by **Dave Boothroyd** » 8 Mar 2004 5:24 am

RMS stands for "Root mean square" - ignore this, and read it as "Average".
If you see a sound wave on a scope, some of the time it at its max, some of the time it's at Zero, and some of the time it's below zero at "minus max". If you took the average of all the values it would normally be close to zero- silence. The RMS thing is a bit of mathematical juggery pokery that allows you to ignore whether the wave is positive or negative and just come up with a value for what the average difference between the signal level and zero is.
RMS power is the power you hear, and the one you need to know to judge the power of your amp.
Cheers
Dave

David Doggett · Post by **David Doggett** » 8 Mar 2004 7:17 am

Okay, so RMS is sort of like standard deviation, in that the root of the squared deviations is taken to get rid of the negative numbers, so you get the average power handling ability. So what is "continuous" power?

Larry Robinson · Post by **Larry Robinson** » 8 Mar 2004 8:05 am

For sine wave AC, the effective or RMS value is equal to the maximum peak amplitude multiplied by 0.707. The instantaneous value is the value that the voltage or current has at any selected time in the cycle. If all instantaneous values in a sine wave are averaged over a HALF cycle, the resulting figure is the average value, which is 0.636 times the maximum amplitude. The RMS value is slightly higher than the average value.

Ray Minich · Post by **Ray Minich** » 8 Mar 2004 8:55 am

One of the reasons RMS is even mentioned is as a way of comparing "heating" values of an Alternating Current signal into a resistor.

Your 120 VAC electrical wiring in your house carries an alternating current of 60 cycles per second and a peak to zero voltage of about 144 volts (if you were to look at it on a oscilloscope you'd see 144 volts between the peak and the zero line, or about 288 volts positive peak to negative peak ). The reason it's called "120 volts AC" is that the 144 volt (peak to zero) sinusoid has the same "heating" effect in a resistor as a DC voltage of 120 volts. Just some more info to add to the confusion.

I have a Fluke True RMS Meter that was made in 1971, for measuring the RMS voltage of really weird waveforms (like trapezoidal, burst pulses, random stuff). The .7071 factor only works for a sinusoid. It's different for square waves, triangular waves, etc. For really weird waveforms the Fluke uses a pair of small temperature controlled ovens. One oven is heated with a constant power level, the other is heated with the input signal (the one being measured) The Fluke uses the differences in temperatures between the two ovens to compute the RMS voltage.
Oops, I made a mistake, the Fluke sent the "unknown" signal to one of the ovens, and then adjusted the control signal to the 2nd oven so that the temperature difference between the two ovens went to zero (like a balance beam). When the two ovens were at the same temp. the control signal equalled the unknown or input signal, and the meter displayed the control signal (RMS Voltage) which was by then equal to the unknown or input signal.
[This message was edited by Ray Minich on 08 March 2004 at 09:00 AM.][This message was edited by Ray Minich on 08 March 2004 at 09:01 AM.][This message was edited by Ray Minich on 08 March 2004 at 09:34 AM.]

C Dixon · Post by **C Dixon** » 8 Mar 2004 9:19 am

The last several posters are correct.

True RMS power (continuous power), RMS power, Peak Power, Peak Music Power, Peak to Peak Power and Peak to Peak music power are all terms that have been used to rate a given amp's power.

I list them in order of being real to ridiculous. So lest there be ANY doubt, MOST authorities including the bureau of standards in Wash agree that the ONLY true power rating is "True RMS power". However the present law insists only on RMS power.

So what is true RMS power versus RMS power versus all the others?

1. RMS power is the average power an amp puts out when fed a continous sine wave signal into it where the amp uses a REGULATED power supply; rather than its own power supply.

As the poster said RMS=Root mean square or; it uses the average voltage of one half the peak to peak voltage of a given signal to determine power. And it is .707 times one half of the Peak to Peak voltage.

So if an amplifier puts out a 200 volt peak to peak voltage as seen on an oscilloscope (just at clipping) when fed a continuous sine wave signal using a regulated power supply, an AC meter put across the output , would read exactly 70.7 volts. Etc.

2. True RMS power is identical to RMS power except the amp must use its OWN power supply. In this case the power rating is always less than RMS power. UNLESS, the amp has a very high quality regulated power supply.

3. Peak power is determined by measuring the peak to peak continuous sine voltage and then halving it. The problem with this and the reason it is not a true rating is, the peaks are ONLY there for a small fraction of the sine wave.

4. Peak to peak power is identical except they do not dived by 2. This is a ridiculous rating and is soooo far out of reality that it is worse than ridiculous.

5. Peak Music power is even worse. It takes into account the fact that music is varying all over the place and a little known fact about amps being able to deliver a tremendous wattage for a miniscule amount of time. This rating uses a regulated power supply instead of the amps own power supply.

6. Peak to Peak Music power is the most absurd rating of all because it exactly doubles the power read in item 5.

This is how it went. Until the government passed strict laws about it, amplifier and stereo manufacturers had their choice of how they rated the power. The more reputable ones used Peak music power. The less reputable ones used peak to peak music power.

ONLY rarely did any manufacturer dare mention RMS power and even today rarely does any one use true RMS power (continous power using the amps OWN power supply).

The government settled on RMS power. This allows each manufacturer to measure the power by using a regulated power supply INSTEAD of the units own power supply. And this has some merit and legitimacy to it.

Because it is true that music is NOT a continous full power medium. So RMS is the name of the game. There are some rogue renegades still out there; and remember our laws do not apply outside our country, so you still have a lot of neubulous terms and chacanery going on.

So here is how it can be stated (not all legal in this country).

An amp that is putting out 70 watts true RMS power will exibit the following:

1. 70-100 (aprox) watts RMS power. Depends on the regulated power supplies efficiency.

2. 100 watts Peak power.

3. 200 watts peak to peak power

4. 150-200 watts peak music power

5. 400-500 watts peak to peak music power

NOW you can see why the government had to step in. It was a joke.

carl[This message was edited by C Dixon on 08 March 2004 at 09:30 AM.][This message was edited by C Dixon on 08 March 2004 at 12:19 PM.]

Gino Iorfida · Post by **Gino Iorfida** » 8 Mar 2004 1:58 pm

Most tube amp guys in the high end business rarely if ever measure the actual output power. Most are just estimates anyways, for example, if they run a quad of el84's at about the same plate voltage as Vox did in the ac30, with a very similar spec' transformer, they will just say it's a 30watt amp, likewaise they will do the same with marshall or fenderesque amps. -- go off of a rough value that is the same as one of the big guys actually did with the amp they base their circuit on (consequently, most amps are measured for power just at the point where distortion occurs, however one can tweak their definitions to make their specs sound better, for example, if one is looking for an amp with big amp cranked sound at lower volumes, they will underrate the output power, if one is looking for ear shattering volumes, they will overrate the power.).

Once again, though, watts mean a LOT less than some other factors, such as speaker/cabinet efficiency, and speaker SIZE!
--a 10" speaker with equivalent efficiency as a 15" speaker will be louder, dute to mroe air being pushed.
-- a more efficient 12" speaker willb e louder than a less efficient 12" speaker etc..
-- a 6 watt fender champ through a 4x10" open back cabinet, with ultra efficient speakers will be LOUDER than a 50watt marshall cranked through a 3" car stereo speaker etc.).... and remember, with all else being equal (i.e. through the same cabinet etc), to double the sound pressure levels (volume), one needs to increase the output power of the amp by a factor of 10! so in other words, a 60watt Fender bassman would only be twice as loud as a 6 watt champ, provided the same speakr is used for both.

Dan Tyack · Post by **Dan Tyack** » 10 Mar 2004 10:35 pm

I know next to nothing about electronics, but I have played for about 8 years through class A amps, mostly. And there is a world of difference in tone between a transistor amp, a class ab tube amp, and a class a amp, especially when the amp is working close to its rated power output.

A transistor amp starts sucking big time when it gets close to rated power, especially if it actually distorts.

An AB amp can sound very good when the power amp section is being pushed, but the distortion from the power stage does tend to sound 'harsh', or at the least, harsher than when clean.

The class A amps I play through (THD Univalve and BiValve amps, an old Supro, a THD prototype) still sound really sweet, even when totally driven. Something to do with the class A amps emphasizing even order harmonics when driven? Who cares, I just love the way they sound. You can play chords with the amp on 10, and still hear the chord definition.

My main amp is a THD BiValve, which is a true class A amp with two output tubes (it is a mono amp with two output sections) It nominally puts out 30 watts or so with my normal setup (a 6550 and a 6L6), but this sucker is way louder than say a Peavey Classic 30. Or even a Marshall 50. I should point out that this stuff is all subjective. I'm sure many people would hate the sound (it's about as far away from a transister steel amp as you could imagine).

------------------
www.tyack.com

John Floyd · Post by **John Floyd** » 11 Mar 2004 1:33 am

And what Carl said is why Ernest said Carvin Watts are much Smaller than other watts. [This message was edited by John Floyd on 11 March 2004 at 01:37 AM.]

David L. Donald · Post by **David L. Donald** » 11 Mar 2004 3:18 am

Dan, which amp or amps did you use on Blackened Toast?

Still one of my favs, I have bought TWO copies.

Oh yeah... who ate the cover art afterwards?

[This message was edited by David L. Donald on 11 March 2004 at 03:19 AM.]

Steve Merritt · Post by **Steve Merritt** » 11 Mar 2004 9:16 am

Ok, here is my question, I have a Standel "Custom" L83 from the early 60's. It is one of the hybrid models with two power tubes, one pre-amp tube AND transistors. So, is this Class A, AB…??? To my ears and taste, the amp sounds great, it’s clean and has lots of power, in some rooms, too much power. So how is this amp rated?

C Dixon · Post by **C Dixon** » 11 Mar 2004 10:34 am

One of the more difficult things to do for the untrained is to try and use, and even more, understand technical terms when it comes to any product in use.

This is never more true than in amplified sound. Such things as the "class" a given tube or transistor operates, bias, grids, plate voltage, B+, impedance, Dolby, Hertz, audio taper, power, gain, "matching", etc, all are highly technical terms which find their way in normal conversation amongst some musicians all over the world.

Sadly, it can be; and often it is more hype than factual. Add to this that nothing on earth is probably more subjective than the perception of sound; and you have a hodgepodge of understanding all the way from totally wrong understanding; to the wisdom of some of the world's most educated and conscientious audio engineers. The latter of which I have sooo very much respect.

This is never more true than when one states how much they like a particular product based on something that product is using from a technical point of view.

Here is why. I can change one component in the preamp section of an amp using class A or class AB outputs stages; and make all the difference in the world in the sound output of said amp.

Now my point is this. If a player buys an amp that has Class AB1 tubes and another player buys and amp with class A output, there is NO way to compare these two amps UNLESS, all other parts are equal. Which is almost NEVER the case.

That is, how does one know that one sounds better than the other because of the class; or whether say the mid circuits in one was tweaked differently than the other is what is causing that sound to be "sooo sweet"; OR both"?

In fact, MOST of the sound "coloring" comes from the preamp section. Particularly when it comes to the "mid" frequencies around 800 HZ. If you have a NV400, you can prove this very easily. Simply set the mid at -3 and have someone move the shift control from one end to the other as you play.

NO other control on that amp has as much a decided affect on sound as that little simple experiment does.

In other words. IF a Class A amp has a mid circuit design that is different than a class AB amp, and it is perceived the Class AB amp is better, there is NO way to say it was because of the class the two amps operated at.

This is why there are zillions of amps and millions of different circuits of every conceivable persuasion out there for sound. And what one uses "because of this or that tecnnical fact", is detested by another for the same technical fact.

YET, each may not be perceiving the tonal difference is because of the "class" (or any other "tecnical fact", but rather, the difference in say the preamp circuitry design, that is perceptibly changing how one's amp sounds versus another amp.

As has soo often been stated on this forum. YOU have to be satisfied; and the best way is for YOU to try it and play it to see if YOU will like it. In most cases, it is doubtful. But every once in a while, fate will smile on you and you WILL find that product that you perceive IS the best.

When that happens, you are truly blessed. So, hold on to that sapsucker like it was pure gold.

Because it is a "true" fact that when YOU are happy with your equipment, YOU will always play better.

And if the "truth" be known, your dear wife will probably be happier too!!

carl

Ray Minich · Post by **Ray Minich** » 11 Mar 2004 12:02 pm

The human ear is a remarkable device. I always remember that the buzzing of a mosquito in your ear is estimated at about 14 femtowatts.
That's 14 times 10 to the minus 15th power or 0.000 000 000 000 014 watts.

[This message was edited by Ray Minich on 11 March 2004 at 12:03 PM.]