AR LS 26 and Pass Labs X350.5 Compatible?

The thing that would be nice to know, to give a better feel for this whole impedance gig, is output impedance vs frequency. All too often manufacturer's supply a single figure for output impedance for say, a tube preamp. It's usually at 1 kHz,and it may be 500-1000 ohms typical. However as 99.9% of the tube preamps on the market implement capacitors to block the high voltage DC, and that good sounding caps have to be a finite size, the output impedance for the typical 6922 or 6H30 design can really rise to the k's of ohms in the lower frequencies. It would be rare for a manufacturer to outright tell you its going to be a bad match, and i'm not sure of the LS26 output impedance across frequency, but into 22 kohms, you will have bass issues if the output impedance is in the thousands of k ohms. Again I have no idea what the ARC is; they might have that data at Pass and can therefore make these recommendations. I know that my BAT Vk5i did not have the energy in the lower octaves as a much simpler solid state source did. I think Bat's do rise way up there in the k ohms region around 20 hz...someone please correct me if i'm wrong...this is not going to be an issue if you are driving a BAT amp (100K) or say 50 K, but the amps that fall into the 22kohm input impedance (come to think of it, this figure, since it is impedance implies frequency dependent variation and it can actually be lower than the specified amount, again why it can be a total crap shoot for brand mix and match)...
Generally the use of this single impedance figure is about as useful (useless?) as damping factors measured at one frequency (pretty much the same thing).
All you can do if you are mix and matching amp and preamp is, if you have not heard the combo elsewhere, pick them so that its not hideously out of whack and simply try it. If it floats your boat you will know it.
Good luck!
Dave

I forgot to mention that I have an X250.5 (same input circuits/same drive impedance give or take as the X350.5).

For the record, let me state that these single data points are pretty useless. They are mostly marketing figures. Think about it folks. Impedance is a frequency dependent resistance to current. On the one had too much data can lead to analysis paralysis, but otoh, too little can lead to bad outcomes. I really appreciate the measurements that stereophile presents when they do equipment reviews. They pretty much cover the spectrum. Of course the final proof is in the listening, and no one can predict that.
Audiofeil, unless these folks have the data in question they are also taking a guess (albeit an educated one at that). Don't get me wrong I love pass products and the company is excellent, but it is what it is.

Bob,
I am somewhat troubled by those findings as well, but when you realize the output capacitance it has to be that way. But it seems odd that ~18k for a sota preamp... this should not be the case. To get the most potential from your system specs like this sort of force you to use amps with at least 50K ohms nominal Zin. There is no getting around it.

Bob, that x10 multiplier "rule" is not something I put much faith in. To actually calculate the drop in dB for this kind of case you simply apply the voltage divider principle at a specific frequency. For example if at 20 Hz the output impedance (what the up stream impedance looks like to the downstream element through same ground return) is 4,800 ohms, and the input impedance at that same frequency is 22,000 (it could actually be different, these are frequency dependent) you get a basic voltage drop of 22k/(22k+4.8k); if it is 1 volt pre divison we are talking 1 v x 0.82, or in dB a -1.7 dB loss. Audible? probably not a whole lot, but that is using these figures. Personally I would rather not like to incur these losses when spending this kind of bread. I would hope that after spending thousands of after tax dollars my electronics can stay razor flat between 20 Hz and 20 kHz. My speakers and room interact to mess the rest of it up but nothing is perfect, eh?

Aurelius,
Any news on the ARC/Pass front?