What is the definition of Class A? - diyAudio
 What is the definition of Class A?
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 17th November 2002, 04:07 PM #1 diyAudio Member     Join Date: Nov 2002 Location: Grenoble, FR What is the definition of Class A? I haven't found anything precise about this what is defining if an amp is class A? are there some equations, ore other requirements? thanks
 17th November 2002, 04:14 PM #2 diyAudio Member   Join Date: Nov 2000 Location: Bangalore, India Transistors conduct current for the full 360 degrees of the cycle in Class A operation. Vivek
 17th November 2002, 04:49 PM #3 diyAudio Member     Join Date: Nov 2002 Location: Grenoble, FR ok but does any relation exist between Vcc and Vds, Vcc and Vg...? I don't clearly understant "conduct for the full 360°"
 17th November 2002, 06:10 PM #4 diyAudio Member     Join Date: Nov 2001 Location: Montreal, Canada The 360 degrees of the sine wave. Class-B would be 180 degrees, half a cyle, while Class-A is the full cycle.
 17th November 2002, 07:17 PM #5 diyAudio Member     Join Date: Nov 2002 Location: Grenoble, FR 360 means a complete phase? So, in a single mosfet amp (like a szekeres like this) It means that -At Vin=0, Vg is at a value where the mosfet conducts -At Vin=max, Vg is still at a value where the mosfet conducts -At Vin=-max (negative peak), always the same... Am I right? What are the maximum peak values of a device's source line output?
 17th November 2002, 10:31 PM #6 diyAudio Member   Join Date: Jul 2001 Location: Orleans, France Yes, you are right. A device (transistor, tube...) which operates in class A is biased so that a current flow anytime across it. This is not the case in class B, because usually positive and negative inputs of the source signal are amplified separately, in symmetric configuration : each of the two devices conducts about half of time. Other classes are unusable for audio, or more complex. Regards, Pierre Lacombe.
 18th November 2002, 10:35 AM #7 diyAudio Member     Join Date: Nov 2002 Location: Netherlands Hi, Simply stated: "Class A amplifiers use one or more transistors that conduct during both the full positive and negative cycles of the signal." However class A is not limited to SS amps. The early Tube ones were all class A. A simple introduction on various classes: http://www.norh.com/docs/amps/

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