Hi Kalali,
As I had mentioned a theoretically ideal voltage source has an output impedance of zero. A real world amplifier cannot have an output impedance of zero, but what allows any amplifier to act as a good approximation of an ideal voltage source is an output impedance that is close enough to zero to be an essentially negligible fraction of the impedance of the speaker.
As you realize nearly all solid state amplifiers do not have output transformers or output autoformers, and consequently do not have multiple output taps. And their rated maximum power capability into 4 ohms will, in almost all high quality designs, be considerably more than their maximum rated power capability into 8 ohms. But while that fact is an **indication** that the amp will act as a voltage source (when operated within the limits of its maximum voltage, current, power, and thermal capabilities), it is not the **reason** the amp will act as a voltage source. The reason is the amp’s very low effective output impedance.
And the McIntosh solid state amplifiers which have output autoformers have effective output impedances that are low enough to be essentially in solid state territory, as opposed to tube amp territory. While as you realize they do not provide the increase in maximum rated power capability for low impedances that is typical of solid state amps. And as I indicated earlier the reason they don’t is that their maximum power ratings are based on the assumption that an 8 ohm load will be connected to the 8 ohm tap, a 4 ohm load will be connected to the 4 ohm tap, and a 2 ohm load will be connected to the 2 ohm tap (with the taps presumably designed such that the output stage of the amp that is "ahead" of the autoformer will see a load impedance that is the same or very similar in each of those three cases, that apparently being the design philosophy McIntosh has chosen for these amplifiers). But what matters with respect to the voltage source question is how the amp will behave when a load impedance that varies as a function of frequency is connected to **one** of those taps. And that behavior depends on the relation between load impedance and amplifier output impedance, as long as the amp is operated within its capabilities.
Also, as I indicated the higher the amp’s damping factor is the lower its effective output impedance will be. The specs you cited for your amp indicate a somewhat lower damping factor for the 8 and 4 ohm taps than I’ve seen for most solid state McIntosh amps that have output autoformers (which as I indicated are usually spec’d at ">40"). But even in the case of your amp’s 8 ohm specified damping factor of only 16, that corresponds to an output impedance of 8/16 = 0.5 ohms. Which is lower than the output impedance of the great majority of high quality tube amps, and is only slightly higher than the output impedance of many solid state amps, and is a small fraction of the impedance of an 8 ohm speaker.
Ergo, while your amp does not approximate a pure voltage source quite as closely as most other solid state amps, or quite as closely as some other McIntosh amps which incorporate autoformers, it still comes pretty close. And as I said, no amplifier can act as a theoretically perfect voltage source. All a real world amplifier can do is to closely approximate one.
Regards,
-- Al
