Quote:
Originally Posted by Charles
I think it's important to match the tap to the impedance of the speaker listed in the specifications. This is what McIntosh recommends. Most amps are built around one "tap". Some amps have no 2 ohm specification for output. It's all about current and stress on the amp caused by the amps inability to supply the necessary current to produce the watts. Asking an amp to supply current for which it cannot easily supply places stress on the amp and the sound quality will suffer. No two Mac amps are the same in this regard. The smaller the Mac amp the more you need to pay attention to careful impedance matching.
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Were speakers actually 2, 4, or 8 ohms this would be a good rule of thumb. However, since we are talking impedance, not simple resistance, and since loudspeakers vary in impedance with frequency, you cannot count on the speakers manufacturer's stated impedance to be the best tap choice. The tube configuration/transformer windings are not the same amp model to amp model, amp manufacturer to amp manufacturer. So some speakers end up on different taps than "spec sheets" would suggest because those "wrong" settings are actually the correct settings, both technically and sonically.
VAC has a nice technical paper ( Can I link a white paper Ivan?) that helps to explain to the layman why the "which tap" answer is variable and not so cut and dried.