Class A vs Class AB

[nauc]

in general, are Class A amps louder sounding than Class AB amps, both amps having the same wattage rating. kinda like a tube amp is louder than a SS amp, even tho they both have the same wattage rating

thanks

 

[rocknhorse1]

Class A and class AB has to do with bias point and output impedance. Although, some amps are just louder than others...just because.

 

[rocknhorse1]

Here is a link
http://www.mylespaul.com/forums/squawk-box/103256-difference-between-class-b-se-vs-pp.html

 

[Buggaluggs]

Class A and class AB has to do with bias point and output impedance. Although, some amps are just louder than others...just because.

Only in this time-space continuum. In others, solid state amps are louder and the Cincinnati Bengals win the superbowl.

 

[axepilot]

Class A and class AB has to do with bias point.

Electronics wise, that is just that. "A" and "AB" are just electronic terms on bias and operation points of an amplifier.................NOT a grade on quality as some ads make it seem.

Don't get sucked into the hype. NOBODY has the ears to tell the difference between A and AB operation of an amp.

 

[Inside Guy]

Watts do not equal decibles. Yes, you can use watts as a guide for how loud an amp might be but it's not a perfect guide.

 

[Splattle101]

in general, are Class A amps louder sounding than Class AB amps, both amps having the same wattage rating....

Short answer, no.

 

[weirdotis]

See here:

Class A vs. Class A/B Guitar Amplifiers

 

[Splattle101]

Consider an output valve (tube). It’s got a big DC current flowing across it. That current is modulated – goes up and down – in response to the signal voltage on the control grid. The up-and-down of the current is what eventually drives the speakers.

This valve has got a maximum and minimum current. The max is when full current is flowing and regardless of how positive we try to make the grid, the current doesn’t increase. The minimum is when we drop the grid voltage so low that the current stops. This is called cut off.

The signal that controls it all is an oscillating voltage. It comes ultimately from the guitar string. It swings positive and negative in time with the note you pluck, causing the current in the valve to go up and down in time with it.

Biasing is about deciding where you set the grid voltage when there’s no signal. If you’ve got one valve, it would make sense to set that bias point about halfway between maximum current and cutoff. So when there’s no signal on the grid, about half of max current is flowing. Then as the signal is introduced, the current goes up and down in time with the signal. On the up-stroke it goes above the bias point, and on the down stroke it goes below the bias point. If the signal is big enough the valve will reach max current on the up-stroke, and go into cut off on the down-stroke. When it does this it is distorting.

The definition of class A is that the valve is biased so that in normal operation (i.e., clean operation), the valve never goes into cut off.

The one-valve amp I’ve just described is a single-ended class A amp, like a Champ.

Class A/B works by splitting the signal voltage. One half stays as it is, but the other half is inverted. It is made 180 degrees out of phase. This job is done by the phase inverter, and thus the name.

The positive half of the signal is sent to one valve, and the negative to the other. However, these valves are biased in class A/B, so the bias point is not halfway between max and cut off. It’s much closer to cut off. The idea is is that when the signal goes on the up-stroke, it has plenty of headroom before it gets to max current. But while one valve is on the up-stroke, the second out of phase valve is on the down stroke. It rapidly hits cut off. On the down stroke, the process is repeated in reverse.

This kind of amp is called a push / pull class A/B amp. It gives you much more power than class A. Consider a Champ. It’s a single-ended, cathode-biased, class A amp with a single 6V6 output valve. It produces about 5 Watts. A tweed Deluxe is also cathode biased, but it is a push-pull class AB amp with two 6V6s. It produces 15 Watts. So it produces not double the power, but triple.

Note well, I’ve not explained push / pull or single ended here. Push pull does not mean class A/B. You can have a class A push pull amp (apparently: I can’t think of one off the top of my head). The thing that determines the class of operation is the bias point. I’ve only explained the bias point.

 

[kysrsoze]

A or A/B likely doesn't mean a damned thing, soundwise. Either one is great if you like the sound of it. A lot of companies brag about their amp being Class A, when it really isn't. But it might sound awesome. It's just a different architecture, and the preamp gives you most of your tone anyway.

I think the same arguments are made about SS vw. tube rectifiers, and fixed vs. C cathode bias. I guess there's some merit to the rectifier comparison. But as far as biasing goes, I'd rather lose 2% of my tone than have to bother with that mathematical equation. Hell, I'll roll a tube before I figure out the bias level... A lot more effective too.

 

[Thumpalumpacus]

My Valveking can go between the two modes. AB puts out more wattage, and to my ears, has a tighter bass, with more thump and a faster response when distorted. The Class A side of things has a softer response, but the trade-off is mushier bottom-end when distorted. It's what I keep it in most of the time, as 1) it sounds more vintage to my ears, and 2) the sweet spot seems broader. I don't play much metal anyway.

I cannot tell much of a difference between the two modes when playing clean tones.

 

[JakeM]

Nauc, ss amps are not rated the same as tube amps. Tubes are measured in RMS not PEAK power, Peak power is the maximum output at full volume. SS amps are generally measured in peak power .

jake

to find peak power from rms, divide the wattage by 0.741

 

[Standard 64]

Consider an output valve (tube). It’s got a big DC current flowing across it. That current is modulated – goes up and down – in response to the signal voltage on the control grid. The up-and-down of the current is what eventually drives the speakers.

This valve has got a maximum and minimum current. The max is when full current is flowing and regardless of how positive we try to make the grid, the current doesn’t increase. The minimum is when we drop the grid voltage so low that the current stops. This is called cut off.

The signal that controls it all is an oscillating voltage. It comes ultimately from the guitar string. It swings positive and negative in time with the note you pluck, causing the current in the valve to go up and down in time with it.

Biasing is about deciding where you set the grid voltage when there’s no signal. If you’ve got one valve, it would make sense to set that bias point about halfway between maximum current and cutoff. So when there’s no signal on the grid, about half of max current is flowing. Then as the signal is introduced, the current goes up and down in time with the signal. On the up-stroke it goes above the bias point, and on the down stroke it goes below the bias point. If the signal is big enough the valve will reach max current on the up-stroke, and go into cut off on the down-stroke. When it does this it is distorting.

The definition of class A is that the valve is biased so that in normal operation (i.e., clean operation), the valve never goes into cut off.

The one-valve amp I’ve just described is a single-ended class A amp, like a Champ.

Class A/B works by splitting the signal voltage. One half stays as it is, but the other half is inverted. It is made 180 degrees out of phase. This job is done by the phase inverter, and thus the name.

The positive half of the signal is sent to one valve, and the negative to the other. However, these valves are biased in class A/B, so the bias point is not halfway between max and cut off. It’s much closer to cut off. The idea is is that when the signal goes on the up-stroke, it has plenty of headroom before it gets to max current. But while one valve is on the up-stroke, the second out of phase valve is on the down stroke. It rapidly hits cut off. On the down stroke, the process is repeated in reverse.

This kind of amp is called a push / pull class A/B amp. It gives you much more power than class A. Consider a Champ. It’s a single-ended, cathode-biased, class A amp with a single 6V6 output valve. It produces about 5 Watts. A tweed Deluxe is also cathode biased, but it is a push-pull class AB amp with two 6V6s. It produces 15 Watts. So it produces not double the power, but triple.

Note well, I’ve not explained push / pull or single ended here. Push pull does not mean class A/B. You can have a class A push pull amp (apparently: I can’t think of one off the top of my head). The thing that determines the class of operation is the bias point. I’ve only explained the bias point.

No offense,I guess if your a builder your responses makes sense,but for some of the average Joes,maybe simplify it a little?Thanks.

 

[Splattle101]

No offense,I guess if your a builder your responses makes sense,but for some of the average Joes,maybe simplify it a little?Thanks.

That IS the simple version.

 

[Standard 64]

That IS the simple version.

ha!!!!

 

[b-squared]

Here's an article from Randall Smith (Mesa Boogie) explaining some of it...it's for guitar players.

BB

Class A - Exposed and Explained by Randall Smith

 

[Koop]

Here's an article from Randall Smith (Mesa Boogie) explaining some of it...it's for guitar players.

BB

Class A - Exposed and Explained by Randall Smith

Excellent article. Thanks for the link.

 

[Mick51]

Great summary, Spattle101. Thank you!

 

[VTchemist]

That IS the simple version.

Agreed. The explanation was the simple one. And it was a good one too.