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RE: Class A power in A/B amp question

"Yes, Class A power will also double when resistance is halved."
He's right - but there's another case to consider. The amp will produce a maximum of 4 watts into eight ohms before moving away from class A operation, but in some cases, such as dynamic or sliding bias arrangements that some amps use, the 4 ohm class A to class B switchover could be at a higher - or lower - voltage / power level.

AND since most of use don't use audio amplifiers to drive resistors, and prefer to drive speakers - the impedance of the speaker will matter. Impedance is a vector quantity, not a scalar like resistance. That is to say, a scalar quantity like resistance has only one characteristic value- the magnitude of resistance. A vector quantity like impedance has both magnitude AND phase angle (and they vary with frequency.) So you'd need to know both of these values at the frequency of interest to predict the Ohm's law current/voltage/power interaction with the amplifier. Makes it more complex, and makes answering the "if 4 watts at 8 ohms how many watts at 4 ohms" a bit more complex, because in addition to 8 or 4 ohms we need to know phase angle to calculate the power.

For those to whom vector quantities are not immediately intuitive, here's an analogy from weather. Temperature - when it comes to a weather report - is a scalar value. It's 35
Science doesn't care what you believe.



Edits: 03/10/19 03/10/19

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