Given the somewhat low input impedance of the Pass amp, specified as 20K single-ended and 30K balanced (those numbers having been essentially confirmed in John Atkinson's measurements), I took a look at the output impedances of the tube preamps listed in the OP for potential incompatibilities.
It should be kept in mind that it is very common for tube preamps to have output impedances at deep bass frequencies that are much higher than their specified output impedances (which are typically at mid-range frequencies). That low frequency rise will occur due to the output coupling capacitor that is used in most (but not all) tube preamps, and will reach a maximum (within the audible range) at 20 Hz.
Chances are that with nearly all tube preamps that will not be of significance to you with your present speakers, because of their somewhat limited deep bass extension. However, it may become a significant factor if you later change speakers, or add a sub that is driven from the preamp's outputs.
Based on my research, I would rule out the Premier 17. From JA's measurements:
Also, the ARC datasheets for all of their models which are listed in the OP recommend a minimum load of 20K (although without indicating whether that applies to their unbalanced outputs, their balanced outputs, or both). So you should be ok with any of those models, but without a great deal of margin.
Regarding the statement by Mr. Pass that is quoted above, while I certainly would not question any statement he might make, when he says "the amp doesn't care about source impedance" I would point out that that does not necessarily mean that the preamp doesn't care about load impedance.
Regards,
-- Al
It should be kept in mind that it is very common for tube preamps to have output impedances at deep bass frequencies that are much higher than their specified output impedances (which are typically at mid-range frequencies). That low frequency rise will occur due to the output coupling capacitor that is used in most (but not all) tube preamps, and will reach a maximum (within the audible range) at 20 Hz.
Chances are that with nearly all tube preamps that will not be of significance to you with your present speakers, because of their somewhat limited deep bass extension. However, it may become a significant factor if you later change speakers, or add a sub that is driven from the preamp's outputs.
Based on my research, I would rule out the Premier 17. From JA's measurements:
The output impedance was below a lowish 800 ohms in the midband and above, but rose to 1.6k ohms at 20Hz, due to the presence of a finite-sized output coupling capacitor. The C-J should therefore be used with a power amplifier having an input impedance of at least 22k ohms if the bass is not to sound a little lean.Also, the Leben preamp models shown at their website (RS38CX, RS-100, and RS-100U) all have specified output impedances in the vicinity of 600 ohms. I couldn't find any data indicating their 20 Hz output impedance, but the 600 ohm figure is high enough to suggest caution. If you want to consider those models, I would ask the manufacturer what their output impedance is at 20 Hz.
Also, the ARC datasheets for all of their models which are listed in the OP recommend a minimum load of 20K (although without indicating whether that applies to their unbalanced outputs, their balanced outputs, or both). So you should be ok with any of those models, but without a great deal of margin.
Regarding the statement by Mr. Pass that is quoted above, while I certainly would not question any statement he might make, when he says "the amp doesn't care about source impedance" I would point out that that does not necessarily mean that the preamp doesn't care about load impedance.
Regards,
-- Al