[plonter]

Hi all. my question is as stated in the subject, what is exactly class operation in amps (...are there any other gear that uses this definitions?)
i mean..class A,B,AB,D, etc..? i never fully got it.

thanks.

 

[ksween93]

The only one I can really give you a definitive answer for is class A. To my simple, limited understanding, class A amps run an electrical current at 100% power through the entire circuit as long as the amp is on. So if you have the amp on and no music is playing, it will use just as much electricity and run just as hot as when you are playing music at full blast. They're really only used in lower power applications (like headphone amps) because as you could imagine, they're pretty inefficient as far a power. But it seems that quite alot of amps are class A. Mine is and it works great.

There's plenty more info at Wikipedia. Electronic amplifier - Wikipedia, the free encyclopedia

 

[plonter]

Quote:

Originally Posted by ksween93 /img/forum/go_quote.gif The only one I can really give you a definitive answer for is class A. To my simple, limited understanding, class A amps run an electrical current at 100% power through the entire circuit as long as the amp is on. So if you have the amp on and no music is playing, it will use just as much electricity and run just as hot as when you are playing music at full blast. They're really only used in lower power applications (like headphone amps) because as you could imagine, they're pretty inefficient as far a power. But it seems that quite alot of amps are class A. Mine is and it works great. There's plenty more info at Wikipedia. Electronic amplifier - Wikipedia, the free encyclopedia

thanks for the info mate, and the link is great...just what i needed.
actually i looked on the internet and couldn't find anything. maybe i should have typed "electronic amplifier" on wiki.

now...i understood the efficiency part of it, but will a class A amp will yield more quality than a class B one?
if class B uses only 50% of the input signal(didn't really got it though...50%??) and class A uses 100% than would class A be better soundwise?

 

[jcx]

I'm afraid you're going to need to find a few more references to get a clearer picture, poor presentation, many unstated assumptins - both the wikipedia and the Rane site assume Class A "Single Ended" - for which practical implementations can be lower than 20% efficient

There is also the possibility of "Push-Pull" Class A where the power in the two active output devices is only a little higher than the max required by load - push pull Class A also can have the highly desirable property of drawing constant current from the power supply over the complete operating range

Class A output circuits can give higher quality amplification because the output devices are never switched off so their distortion characteristics are much lower order (smoother relation between drive and output V)

For Headphone power levels (typically <1W) the low efficiency of Class A is of little concern for desktop amps, for battery power most people are unwilling to carry the large power supply needed for full Class A operation

 

[plonter]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif Class A output circuits can give higher quality amplification because the output devices are never switched off so their distortion characteristics are much lower order (smoother relation between drive and output V)

thanks, but i still don't undrstand...what do you mean by "never switched off"? or should i ask...if in class B,C,D etc. , output devices are beeing switched off,than how can i listen to music through them? the amp doesn't just turn off or something...so what does that mean?

doesn't the output stage need always to be on?

 

[slackman]

As far as I understand it, this is not thesame "off" as hitting the off switch of the amp

Sound is a wave-form in electrical current through the amp.
If I'm correct push-pull uses 2 amps per channel. One amp only amplifies one part of the waveform, lets say the + part (the actual electric sound wave is cycling between + and -) where the original wave has for instance a maximum + part of +1 this amp will make this +1 into a +4 for instance. It doesn't touch the - (minus) part of the waveform, so as soon as the minus part of the waveform comes in it switches off (so for a 1Khz sine it switches on and off 1000 times per second).
The other amp per channel is the used exactly thesame but for the - (minus) part of the electrical soundwave (and switches off when the wave becomes + again).
I beleive one of the reasons this amp design often has higher distortion is because in practice the 2 amplified wave halves per channel do not match up / glue together again as perfectly as the original signal.

A true class A amp however amplifies both the + and the - parts of the wave and never "turns off".

Someone correct me if I'm horribly wrong but I read some about it long long ago and this is how I remember it.

 

[plonter]

Quote:

Originally Posted by slackman /img/forum/go_quote.gif As far as I understand it, this is not thesame "off" as hitting the off switch of the amp Sound is a wave-form in electrical current through the amp. If I'm correct push-pull uses 2 amps per channel. One amp only amplifies one part of the waveform, lets say the + part (the actual electric sound wave is cycling between + and -) where the original wave has for instance a maximum + part of +1 this amp will make this +1 into a +4 for instance. It doesn't touch the - (minus) part of the waveform, so as soon as the minus part of the waveform comes in it switches off (so for a 1Khz sine it switches on and off 1000 times per second). The other amp per channel is the used exactly thesame but for the - (minus) part of the electrical soundwave (and switches off when the wave becomes + again). I beleive one of the reasons this amp design often has higher distortion is because in practice the 2 amplified wave halves per channel do not match up / glue together again as perfectly as the original signal. A true class A amp however amplifies both the + and the - parts of the wave and never "turns off". Someone correct me if I'm horribly wrong but I read some about it long long ago and this is how I remember it.

thanks slackman, i think i got the principal of it.