amplifier classes

[{ antonio }]

right now i am studying for a class.  and i figurred that everyone here might be able to answer this question.  

i wanted to know if anyone knows the difference between the classes of amplifiers.

i understand the efficiency portion of them (ie class a is only 25% efficient)

but what are the physical differences.  (ie what schematics or basic cookbook designs are used to define each of them.

any help and links are  greatly appreciated.  thanks. :wink:

[toneman]

tried googling??

tb

[jjs]

You could try the "tech info" section on www.aikenamps.com. Many information there.

[Kaiowas]

http://sound.westhost.com/class-a.htm

This speaks mostly about Class A, but it also has some info about the others and some comparisons

[niftydog]

try good ol' tpub.com!

Class A amps are single transistors, biased in the middle between cut-off and saturation.  Collector current flows for 360 degrees.

Class B amps are usually two transistors in a "push-pull" configuration, both biased at cut-off.  Collector current flows for 180 degrees in each transistor, making up the full cycle.

Class C amps are single transistors, reverse biased, and only conduct for less than 180 degrees.   They use resonant circuits to "recreate" the sine wave.  Normally used for RF amps and oscillators.

Don't ask me about class D... haven't sat down and looked into them yet.  There's heaps of others, but they're variations on the above.

[csj]

shalom antonio,

As a very bare minimum consider this...

How a device conducts current throughout the input signal's voltage cycle determines it's class of operation. In effect it's actually a ratio between the
the device's (tube or transistor) current at idle and its peak current.

Class A ops allow for the signal to be driven completely through its 360 degree cycle without ever dipping down to the cut off point (the place where conduction stops). These devices conduct constantly; more or less depending on the point of the signal cycle.

The other classes beyond this (and there are many) all vary by setting different points on the signal curve at which to stop the device from conducting.

The classes may be mixed e.g. class AB
or modified e.g. class A2... etc.

This is just a start for a somewhat complex subject...

Good luck on your test.

[Paul Marossy]

Most tube amps are either Class A (supposedly Vox AC30 and similar amps) or Class AB (Fender, Mesa Boogie, Marshall and tons of others)

Then there is sub-classes like AB1, etc.

Here's a little page on that: http://www.zwengelamps.com/classes.html

[Brian Marshall]

Class D amps are either off or on, and nowhere inbetween.  You can use PWM at a high frequency, and a low pass filter to recreate audio.

Brian