CLASS A AMPLIFIERS

Charlot

To keep it simple - the benefit of the Class A amplifier is in it's sonic product! This is one of those things that is ineffable and must simply be heard and compared.
I have been listening to Class A amplification since the late 1990's and have no complaints. In 2005, I built a 1 watt SET that currently supplies my sonic entertainment.

Keep in mind that transistors as well as tubes can run in Class A. In fact, transistors in Class A come pretty close to doing tube-like stuff sonically.

Hope this helps.

Studio1

Spear11,

It depends on the amplifier; the regulation of its voltage and its current output capacity.

We've been discussing amps that "double down" - those that will double their power
if the load impedance is halved. If we let V be the RMS voltage; then we can use
equations for power that look like the DC equations - but the use of the RMS values
make them applicable for AC power.

For a voltage source, the power P = V^2 / R; or P*R = V^2 = a constant if V is strictly
regulated. If the amp is rated at 200 watts at 8 ohms, then V^2 = 1600 volt^2. For
your 3 ohm speakers, P * (3 ohms) = 1600 volt^2.

Therefore, P = 533.3 watts.

Now this also presupposes that the amp has the current reserves to fulfill this. For
200 watts at 8 ohms; the current is given by P=(I^2)R; so that the current I = 5 amps.
For 533.3 watts at 3 ohms, the current will be 13.33 amps.

IF [ big IF ] the amp has the current reservers to output 13.3 amps, and the voltage is regulated to be the same irrespective of load impedance; then this hypothetical amp
can put 533.3 watts into the 3 ohm load.

Dr. Gregory Greenman
Physicist

The Pass XA.5 series is single-ended, class A, and doubles down going from 8 ohms to 4 ohms.

>> 01-19-06: Aball
>> No. The sonic benefit is that the entire signal is
>> swung by a transistor (or several in parallel) instead
>> of individual halves of the signal being split up by
>> two different transistors. Since there is no "handing
>> off" of the signal to another transistor, there is
>> potentially less distortion.

I hate to say this Aball - what you have explained above is single-ended operation & not class-A operation!
it just so happens that many/all single-ended tube & s.s. amps are class-A.
For class-A operation the transistor is biased along the load line in such a way that it always has max current flowing thru it whether a music signal is input into it or not. hence the heat dissipation.
s.s class-A amps can be single-ended (Aleph series) or can be push-pull (almost every other model).
In push-pull you will have P & N type transistors but it is not necessary. For example the Plinius SA-250 has N type push & N-type pull. Slightly higher output impedance i.e. lower damping factor but all N types can be matched better.
I'm sure that you know all of this as you are trained as a EE, I think? Probably wrote your post in a hurry or while cramming for an exam the next day?
FWIW.