What are the difference between CLASS A and PURE

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.