Are There Any Inherent Advantages to Class A amps?

"A Class A amp can't switch to Class A/B--it doesn't have
the second "mirror-image" amplifier chain to handle the
opposite polarity. An amp that is Class A only has a single
chain--and it is biased so that it conducts during 100% of
the cycle--both positive and negative."

Morbius, that's not correct. You're confusing 'single-ended' with 'class a'. The first is a circuit-design principle wherein one output device does indeed handle both swings of the alternating-current signal. The 2nd deals with how much bias current is pushed continously thru the output device(s). Every solidstate class-A amp I know of (and that's not many) is push/pull and NOT single-ended.

These are 2 different design considerations.

Jeffreybehr,

You are incorrect my friend, a single ended amp is just a Class A amp with a single (as opposed to multiple) devices in the output stage per channel. Class A amps BY DEFINITION amplify through 360 of the duty cycle. Class A amps ARE NOT push pull!!!

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

Class-A Output device(s) conduct through 360 degrees of input cycle (never switch off) - A single output device is possible. The device conducts for the entire waveform in Figure 1
Class-B Output devices conduct for 180 degrees (1/2 of input cycle) - for audio, two output devices in "push-pull" must be used (see Class-AB)
Class-AB Halfway (or partway) between the above two examples (181 to 200 degrees typical) - also requires push-pull operation for audio. The conduction for each output device is shown in Figure 1.
Class-C Output device(s) conduct for less than 180 degrees (100 to 150 degrees typical) - Radio Frequencies only - cannot be used for audio! ** This is the sound heard when one of the output devices goes open circuit in an audio amp! See Figure 1, showing the time the output device conducts (single-ended operation is assumed, and yes this does work for RF)
Class-D Quasi-digital amplification. Uses pulse-width-modulation of a high frequency (square wave) carrier to reproduce the audio signal - because of frequency limitations (and the fact that they nearly all seem to sound disgusting), many are only suitable for industrial control of motors and loud but crappy sub-woofers (this may change if transistors with an infinite bandwidth become available soon - yeah, right!) All Class-D amps have a major limitation in the output filter, whose response is highly dependent on the load impedance.

Well, we seem to be splitting hairs here.

I was specifically addressing Morbius's comment, which is still incorrect in that class-A amps can indeed be push/pull as are all the solidstate class-A-biased amps I've ever seen (and, as I said, that's not many, as I do not study everything this crazy industry markets).

So I'll agree that the output devices of push/pull class-A-biased amps do indeed conduct the entire waveform if you'll agree that Morbius's statement is incorrect.

Jeffrey,

We are NOT splitting hairs - go back and read Steve's post -
where he states, "Class A amps BY DEFINITION amplify
through 360 of the duty cycle. Class A amps ARE NOT
push pull!!!"

A true Class A amp does not have two "mirror-image"
amplifier chains - one for the positive half of the wave,
and one for the negative half of the wave - as is found in
push/pull.

In a true Class A amp, a single amplifier chain is biased
to conduct through all 360 degrees of the waveform.

Dr. Gregory Greenman

Please help me out here. There seem to be lots of conflicting definitions of class A. The references Tripper cites clearly indicate that class A can be a push pull design. Virtually everything I've read in the past here on the Gon also support that. I'm wondering if the definition that Stevechan cites is also consistent with that: The definition for class A reads that "a single output device is possible" -- I would interpret that as "possible", not "required". If someone elects to provide the bias for 360 operation but also elects push-pull, then it may still be class A. The definition for class B indicates that "push pull must be used". That is true. It must be used in class B designs for the full wave form -- and depending on bias, the full wave form may not be reproduced at some volumes even with push pull. I don't believe the definitions are at odds. The definitions per Steve allow for push-pull in A but insist on push-pull for B. That is consistent with the definitions supplied by Tripper. I may be missing something -- besides my mind, which I know is gone ;-)