Anyone have any thoughts the previous question about what specs to look at when making sure the amp and preamp tube are compatible?
The usual concern when using a tube preamp together with a solid state power amp is impedance compatibility. Ideally the input impedance of the power amp should be at least ten times greater than the output impedance of the preamp, at the frequency within the audible range for which the output impedance of the preamp is highest. That frequency will usually be 20 Hz, as a result of the impedance rise caused at low frequencies by the output coupling capacitor most tube preamps use.
A factor somewhat less than 10x may or may not be acceptable, depending mainly on how the preamp's output impedance varies as a function of frequency, and on the deep bass extension of the speakers.
I see that the amp's input impedance is 33K. The Little Dot preamp you are considering has a specified nominal output impedance (presumably at mid-range frequencies) of 600 ohms. The corresponding figure for the AES is 560 ohms. I couldn't find a number for the Dared.
It is possible that those figures will rise at deep bass frequencies to levels that would not meet the 10x goal, conceivably causing a slight rolloff of the deepest bass. I suspect that if that were to occur, it would be so slight as to not matter, but if you want to pursue those models see if the manufacturers can tell you what their output impedance is at 20 Hz.
Another factor to consider, especially given the high sensitivity of your speakers, is to avoid preamps having particularly high gain. Otherwise you may wind up having to use the volume control in the preamp too far down in its range, with the DAC's volume control at max (where it ideally should be). The Little Dot seems ok in that respect, its gain being adjustable to 3x (about 10 db). The AES's specified gain of 15 db may be getting into uncomfortable territory.
Regards,
-- Al
