Does that power calculation hold true if the amp is single ended and not push pull? I know it is class A, but it is not a PP design.
I thought the Pass manual said the amp could do the same power into any load (at least for the X series).
The amp is spec'd at 30W into 8 ohms, and 60W into 4 and 2 ohms. Stereophile measured a bit more than 32W into 8 ohms, 55W into 4 ohms, and 39W into 2 ohms.
What
the manual says is constant is not power delivery, but power draw. See the second paragraph on page 10, which says that "the power draw of this system is constant regardless of the music playing through the amplifier."
From that we can infer that the power draw will be the same with a 16 ohm load as with an 8 ohm load, because if the music waveform is zero volts no current or power will be drawn by either load. Therefore the amp's internal voltage rails, and the amp's output voltage swing capability, will not increase as a result of reduced current demand by the 16 ohm load. That is why I mentioned the fact that the amp is pure Class A.
The low output impedance (typical of solid state amps, of course) means that the amp behaves essentially as a voltage source, within the limits of its current capability. The fact that it can nearly double power into 4 ohms relative to 8 ohms confirms, as might be expected, that its 8 ohm power delivery is limited by voltage swing capability, not by current capability. Its 16 ohm power delivery will be limited by that same voltage swing capability.
Therefore based on P = (Esquared)/R, the maximum power that can be delivered into 16 ohms will be very close to 1/2 of what can be delivered into 8 ohms.
The fact that the amp is single-ended rather than push-pull does not change any of that.
Best regards,
-- Al
