04-30-15: Rebbi
So it makes me think that when looking for a speaker for this kind of amp, it makes some sense to look at brands that are not only high-efficiency and flat impedance, but also otherwise designed with single ended operation in mind. Again, I don't know the physics and engineering of this, but there must be other factors involved in designing a speaker specifically to be "SET friendly."
Almarg, feel free to chime in here. :-)
I don't know either, Rebbi. And in the absence of empirical inputs from users and/or the manufacturer, I doubt that it could have been predicted based on its published and measured characteristics that the De Capo would have any particular synergy with SETs (within the maximum volume capability of the combo). Although as you realize the De Capo's relatively benign impedance characteristics at least do not exclude the possibility.
Some very speculative guesses, though, as to things that might be contributing factors:
1)Although I haven't seen any frequency response specs or measurements on the Kit1, I would suspect that it has a more limited bandwidth at both ends of the spectrum than most push-pull amps. Perhaps that helps to keep frequencies out of the De Capo that don't have much if any audible significance but that it might not be able to handle comfortably (i.e., without intermodulation or other effects that could result in those frequencies affecting audbily significant frequencies).
2)Perhaps the design of the De Capo is such that it particularly benefits from the enhancement of dynamics that SETs will tend to provide, as Ralph/Atmasphere has explained is a consequence of how their distortion characteristics vary as a function of signal level.
3)As shown in the NRC measurements, the De Capo's impedance has a sharp rise to about 30 ohms in the vicinity of 70 Hz, where a lot of energy is often required. Relative to its rated power capability, a SET will be able to deliver more power into that high impedance than most push-pull amps, especially solid state amps.
As I say, though, those are all just speculative guesses as to what might be contributing factors, and I don't think that this particular synergy (within the maximum volume capability of the combo) could be either ruled out or ruled in "a priori." So I agree with the comment by Charles just above.
Best regards,
-- Al
