What are the difference between CLASS A and PURE

Thank you to all of you.
It’s been a wild ride for my stereo, my wallet and me in the last 3 months.
Everything start with the born of my new baby boy when my wife told me Paulo you need to sale some stereos and speakers that you are not using we need the room. So I did decide that was a great opportunity to reduce quantity but up-grade in quality. So here we go in my 3 month roller coster.
I did change everything except for my speakers Martin Logan Aerius I and my CD player a Marantz 67SE.
I had a Sony Preamplifier a Sony MD and a Parasound HCA-1000A power amplifier, then two HCA-1000A running my Speakers bi-amp.
Then I bought an Audio Research SP-9 preamplifier and an Audio Research D-90 power amplifier to replace my sony and my two parasounds and bought a turntable.
However the D-90 power amp works but on the shipping was bang by UPS, so the insurance from UPS is paying me back. Same thing with the first turntable I bought.
So I bought a New Turntable two weeks ego and yesterday I bought a B&K 4420 power amplifier and a Audio Research D-200 and I’m planning to keep them till I decide which one I will keep. (Probably will keep the Audio Research because should sound better and second I love the looks on Audio Research). Neither one arrives home yet. Probably in a week from now I will be able to compare them.
Paulo Ramirez

Class A and Pure Class A are mainly the same thing, switvhng A to AB amps ae always indcated in the specifications sheet, some examples of class A amps are Gryphon Anthileon or the DM100.

Class A amps are energy savings enemies, but sound the best IMHO.

Fernando

Think of Pure Class A and Class B as defining the endpoints of a spectrum. The zone between them is Class AB, and AB1 and AB2 are simply defined points on the spectrum.

Consider amplification of a sine wave. The entire output stage on a Pure Class A amp conducts on all 360 degrees of the waveform. The topology may be single ended or push-pull.

A pure Class B amp must be push-pull. Each half of the output stage conducts for exactly 180 degrees of the waveform before the other half takes over for the remaining 180 degrees.

A Class AB amp must be push-pull. Each half of the output stage conducts for more than 180 degrees of the waveform. The limiting case of this is that both halves of the output stage conduct for 360 degrees, or pure Class A operation.

Depending on design parameters, an amp's class of operation may vary with signal level, so that the output stage operates in Class A for relatively small signals but smoothly moves into AB operation at higher signal levels. The stronger the signal and corresponding power output, the further into Class AB the amp operates.

Raul,

I have some Yamaha amplifiers (M-80 and M-40) that have "Class A" switches on them.

Normally, the amps operate in class AB mode with output of up to 250wpc (for the M-80). But, if you engage the "Class A" switch, the amp will operate in Class A mode to approximately 30wpc (for the M-80), then automatically go to AB mode for >30wpc.

The downside is, of course, the amps run much hotter with the "Class A" switch engaged.