Class A vs A/B

[SlagJones]

Is there a tonal difference between class A and class A/B tube amps? Any other significant advantages or disadvantages between them?

[copper1281734000]

There is a difference in tone between them, but I don't know it. When I buy amps, I just find one that sounds good. Class A or A/b really means nothing if the amp sounds good (or bad).

[layboomo]

Go here http://www.aikenamps.com/ and look at "The Last Word on Class A"......probably more than you want to know about amp classes.

[SlagJones]

An interesting read and you are right much more than I wanted to know.

I was simply looking for anecdotal comments like "Class A sounds dirtier to me when you crank it up" or whatever.

Any real world opinions out there?

Of course I wouldn't base a purchase on what I haven't heard with my own ears, really just posting out of curiosity and seeing if anyone had any comments on the subject. Thanks.

[SlagJones]

An interesting read and you are right much more than I wanted to know.

I was simply looking for anecdotal comments like "Class A sounds dirtier to me when you crank it up" or whatever.

Any real world opinions out there?

Of course I wouldn't base a purchase on what I haven't heard with my own ears, really just posting out of curiosity and seeing if anyone had any comments on the subject. Thanks.

[m-theory]

Class A will have more even order harmonics, which translates into a "sweeter distortion." A/B would have more "swirl" or thickness/complexity to the distortion.

[copper1281734000]

If you want a VERY complex answer to what class A is there's a whole page of it on the mesa boogie website. Here's a link:

 

http://www.mesaboogie.com/US/Smith/ClassA-WebVersion.htm

 

It's probably a little more information than you want, but If you're interested (and have enough time on your hands) then read it. I don't have an attention span long enough to read it so I haven't, but some people might find it interesting.

[cGil]

Single Ended power amps generate gobs of even order harmonics. Generally, cathode bias is thought to equate to class A operation, but the VJr has plate voltage and bias that brings it closer to class AB than class A. So get past the "class" BS that feeds the hype machine written by clueless non-technical newbs, and put more focus on things like SE or P-P, and cathode bias or fixed bias. A fixed bias pulls the control grid to a negative potential and gets max power out of the tube. In the case of the el84 in SE configuration, about 7watts.

 

Push Pull power amps are more efficient, getting 15 to 18 watts in cathode bias, and 20 to 22 watts fixed bias. Regardless, when balanced they self cancel heater hum and rectifier noise, as well as even order harmonics, leaving behind odd order harmonics. But even "matched" tubes will drift, thereby allowing some of the even order harmonics to sneak back in. The more out of balance the power tubes, the quicker they'll distort, so unless you're looking for max clean headroom, tube matching in a properly designed push pull amp isn't really so necessary as they'd have us believe. Amps are really very flexible and forgiving.

 

Gil...

[layboomo]

Single Ended power amps generate gobs of even order harmonics. Generally' date=' cathode bias is thought to equate to class A operation, but the VJr has plate voltage and bias that brings it closer to class AB than class A. So get past the "class" BS that feeds the hype machine written by clueless non-technical newbs, and put more focus on things like SE or P-P, and cathode bias or fixed bias. A fixed bias pulls the control grid to a negative potential and gets max power out of the tube. In the case of the el84 in SE configuration, about 7watts.

 

Push Pull power amps are more efficient, getting 15 to 18 watts in cathode bias, and 20 to 22 watts fixed bias. Regardless, when balanced they self cancel heater hum and rectifier noise, as well as even order harmonics, leaving behind odd order harmonics. But even "matched" tubes will drift, thereby allowing some of the even order harmonics to sneak back in. The more out of balance the power tubes, the quicker they'll distort, so unless you're looking for max clean headroom, tube matching in a properly designed push pull amp isn't really so necessary as they'd have us believe. Amps are really very flexible and forgiving.

 

Gil...[/quote']

 

Very well stated as usual Gil!