Thanks Bruce; I've learned a new word today :-)
As I indicated, the MC205, as well as the MC solid state amplifiers that use autoformers (which the MC205 does not use), have negligibly small output impedances. The MC205 is spec'd as having a damping factor of 140, corresponding to an output impedance of 8/140 = 0.06 ohms. So it will act as a voltage source with respect to the interaction of its output impedance with the speaker's impedance vs. frequency variations.
Which means that for a given signal level at the input to the amplifier it will output twice as much power at frequencies for which the speaker's impedance is 4 ohms as it would deliver at frequencies for which the speaker's impedance is 8 ohms, and half as much power into 16 ohms as into 8 ohms.
PROVIDED, however, that the maximum limits of its power capability are not exceeded. What will NOT double into 4 ohms, compared to 8 ohms, is the MAXIMUM amount of power it can put out. And I suspect that if the rear panel switch were set to 8 ohms and the impedance of the speaker is close to 4 ohms in most of the bass region, its MAXIMUM power capability into that 4 ohms would be significantly LESS than the 200W it could deliver into 8 ohms at that setting.
Basically, what the switch is apparently doing is optimizing internal voltage, current, and thermal operating conditions for whichever of the two load impedances is selected, such that a maximum of 200W can be delivered into either impedance.
Best,
-- Al
As I indicated, the MC205, as well as the MC solid state amplifiers that use autoformers (which the MC205 does not use), have negligibly small output impedances. The MC205 is spec'd as having a damping factor of 140, corresponding to an output impedance of 8/140 = 0.06 ohms. So it will act as a voltage source with respect to the interaction of its output impedance with the speaker's impedance vs. frequency variations.
Which means that for a given signal level at the input to the amplifier it will output twice as much power at frequencies for which the speaker's impedance is 4 ohms as it would deliver at frequencies for which the speaker's impedance is 8 ohms, and half as much power into 16 ohms as into 8 ohms.
PROVIDED, however, that the maximum limits of its power capability are not exceeded. What will NOT double into 4 ohms, compared to 8 ohms, is the MAXIMUM amount of power it can put out. And I suspect that if the rear panel switch were set to 8 ohms and the impedance of the speaker is close to 4 ohms in most of the bass region, its MAXIMUM power capability into that 4 ohms would be significantly LESS than the 200W it could deliver into 8 ohms at that setting.
Basically, what the switch is apparently doing is optimizing internal voltage, current, and thermal operating conditions for whichever of the two load impedances is selected, such that a maximum of 200W can be delivered into either impedance.
Best,
-- Al