So here is my question. What is happening electrically if there is an
impedance mismatch? Is the amp producing distortion if there is an
impedance deviation from 3000 ohms? If so, does having larger wattage
and power supply capabilities ameliorate distortion effects?
How
about negative feedback? In my case, I understand that the Ref 150
uses 14db of negative feedback and as a result, performs like a voltage
source amp. Does that feature help to reduce distortion effects?
I
have not touched on phase angle or sonic coloration issues caused by
impedance mismatches between the amp's output taps (nominally, the 4, 8
or 16 ohm taps) and the speaker's actual impedance at a particular
frequency.
As to sonic coloration, I recall that the output
impedance of the ARC Ref 150 off the 8 ohm taps is around 1 ohm or
less. This results in some sonic coloration, ... but not a lot. In a
Stereophile review of the ARC Ref 150, John Atkinson measured the Ref
150's voltage output variation off the 8 ohm taps to be (+) or (-) .8 db
when presented with a synthetic speaker load.
Btw, are similar issues presented with OTL tube amps?
@bifwynne All amps always make distortion. If the amp's tubes are loaded below 3000 ohms, distortion will rise. If loaded above that, its power will decrease as will its distortion.
The feedback allows the amp to behave as a voltage source. George has it wrong; the amp can make double the power into 4 ohms as it does into 8 because voltage sources do that (this is by definition). The deal is, the 4 ohm power is the maximum power for which the amp is rated and you have to be on the 4 ohm tap. If the impedance then rises to 8 ohms, the amp will make 1/2 of its output power. Its a bit confusing, because tube amps accomplish the task of being a voltage source in a way that is opposite of how solid state amps do it.
The issues are the same with an OTL, but of course no transformer is (usually) involved. Instead the tubes see the load directly.
