Having only recently taken a genuine intereste in Hi Fi, I've taken a similar route to a number of other newbies and read quite a few magazines.

In descriptions of Amps I've read about Class A, Class AB and even something towards the end of the alphabet when discussing digital output.

Can anyone explain what the difference is?

Apologies for my ignorance.

Hi Patrick, wasn't sure myself TBO but i've stumbled across an in-depth article on the web:

"A class A amplifier is defined as one which is biased to a point where plate current in all the output devices flows for the entire 360 degrees of an input cycle, at the full, unclipped output of the amplifier.  This is typically done by biasing the output stage halfway between cutoff and saturation, with the plate load impedance to an appropriate value that gives maximum undistorted output power.  This is the least efficient method of amplification, because the output devices are dissipating maximum power with no input signal.

A class B amplifier is one in which the grid bias in all output tubes  is set at cutoff, i.e., no plate current flows in the absence of an input signal.  Plate current only flows when a signal is present, and only flows for exactly half, or 180 degrees, of the input cycle."

Does that make sense to you?? It's a bit over my head!

I agree with you Nick, it all sounds very good but I don't really know what it means. Anybody fancy translating it for us?

Hi Guys, I think this is what it means

Class A: Positive and Negative cycles run together, very pure sound but the amp runs very hot as I'ts always on even when not playing music. Normally Produces less power as well.

Class B Positive and Negative run on seperate circuits, it runs cooler but the sound isn't as pure.

The easy way to hear some of the differnce is to listen to a Marantz PM7200 or 7200KI that has a class A/B button allowing you to change modes. Class A is supposed to be very sweet and Class B is a party Animal.

hi folks.pure class A also removes 2 nasties in your amp.cross over and switching distortion.in a class B the output transistors switch on and off,and switch between left and right.class A a constant voltage is used.even at idle your class A IS STILL WORKING HARD.about 75-80% of your power is wasted as excess heat.now for the good bit.a midrange to die for,the bass.ask my neighbors in the other 7 flats about the bass.low power! im using 25 watts per channel.with a Linn Kollector on 35 its amusing.{line level)phono on 50 is well shall we say,i,ve had people drop mugs of tea! it,s all down to the amps power supply.some are better than others.ie sugden,musical fidelity,budget,rotel,cambridge,nad.ps you dont have to spend a fortune.go back,go back in time.use the classifieds and save a fortune....i/k..

Hi Ian
I agree with Ian about using the clasifieds I'm running an Arcam CD 82, Linn Kolektor and 2 LK85s into Ruark Prelude 2s, all either second hand or ex-dem, the lot cost me about £1500. And there's some lovely second-hand kit out there on ebay and hififorsale.com

Mark