P.S: Here are examples of what I was referring to, about the output impedances of some PrimaLuna amps:
From Stereophile’s review of the DiaLogue Premium power amp:
From their review of the ProLogue Premium power amp:
But on the other hand, from their review of the DiaLogue Premium HP integrated amp:
I can't say which of these models would sound best with your Cornwall IIIs. But what I can say is that given the very wide variation of the speaker's impedance over the frequency range these three amps will sound significantly different with those speakers.
Regards,
-- Al
From Stereophile’s review of the DiaLogue Premium power amp:
The output impedance varied widely, from an extraordinarily high 15 ohms with EL34s and 14 ohms with KT120s from the 16 ohm tap, both tubes in Ultralinear mode, to 2.4 ohms with EL34s and 2.15 ohms with KT120s, both tubes in Triode mode, from the 4 ohm tap. The output impedance from the 8 ohm tap was lowest with both tubes in Triode mode, at 4.6 ohms (EL34s) and 3.9 ohms (KT120s). Changing to Ultralinear mode raised these impedances to 7.9 and 7.4 ohms, respectively.
With these high output impedances, the DiaLogue Premium’s frequency response will be altered to a significant extent by the Ohm’s law interaction between these impedances and the manner in which the loudspeaker’s impedance changes with frequency.
From their review of the ProLogue Premium power amp:
The output impedance from both output taps was significantly higher than that of the ProLogue Premium integrated amplifier. From the 8 ohm tap, I measured 9.2 ohms at 20Hz, 8.75 ohms at 1kHz, and 8.45 ohms at 20kHz; from the 4 ohm tap, the respective impedances were 4.7, 4.5, and 4.35 ohms. As result, the variations in frequency response with our standard simulated loudspeaker were extreme, reaching ±3.1dB from the 8 ohm tap (fig.1, gray trace), and with a large drop in level each time the load impedance was halved (cyan, magenta, and green traces). As expected, these variations were smaller from the 4 ohm tap (fig.2), but the matching between channels was excellent from both taps.
But on the other hand, from their review of the DiaLogue Premium HP integrated amp:
The output impedance depended on frequency, the transformer tap, and the mode of operation. The lowest impedance was from the 4 ohm tap in triode mode, at 1.1 ohms from 20Hz to 1kHz, rising to 1.33 ohms at 20kHz. Ultralinear mode slightly increased both of these impedances, by 0.1 ohm, while the 8 ohm tap almost doubled them. Even so, these impedances are significantly lower than with other PrimaLuna amplifiers I have measured, and the modulation of the amplifier’s frequency response by the interaction of its output impedance with that of the loudspeaker was relatively mild.
I can't say which of these models would sound best with your Cornwall IIIs. But what I can say is that given the very wide variation of the speaker's impedance over the frequency range these three amps will sound significantly different with those speakers.
Regards,
-- Al