Another point of interest worthy of mention is that the D11 II has an impedance selector switch in the back, (my AU-G77X also has one), whereas the regular D11, does not.
The first thought that comes to mind is why would the D11 II, with its very large toroidal transformer, extra wattage (130 vs 120 on D11) and so forth, need an 8/4 ohm selector switch, but not the D11? (or choose any other model, say, why doesnt a 9090DB need one?)
Well, it just so happens that there is some Information about this in the latest issue of The Sensible Sound magazine, page 19-20, to be exact. The reasons why as written in the mag are in regard to current-day Yamaha receivers, but the same idea applies to vintage amps as well, I believe.
The writer states that the main reason for the switch has to do with the model being able to pass the rigorous UL (Underwriter Labs) thermal test Certification. The point is that the amp CAN probably drive low impedance speaker loads ok, but having the switch there will make sure that the amp runs cooler into lowZ loads, because when the switch is set to 4 ohms, the voltage to the amp's power supply will be reduced, (approximately 10 to 25%). And thus, you can see there is a tradeoff: lower operating temperature vs reduced max power delivery.
The writer states that an amp with such a switch, CAN be left in its 8 ohm position (for max power delivery) when driving 6 or 4 ohm loads and everything should be fine, unless the speakers youre using are really very inefficient and the listening room is very large, thus putting more demand on the amp, in which case, you can switch it back to the 4 ohm setting if you find that the amp is getting very hot at the 8 ohm setting.
I find this is useful Info to be aware of, however, the D11 II's internal heat sinking system looks to be quite good to me, so I still dont see why an impedance selector switch is on there.
B/F
