AR LS 26 and Pass Labs X350.5 Compatible?

Aurelius, I have a Audio Research Ref3 and had it paired up with PASS X-600.5's and that was a great combo driving Eggleston Andra 2's.

One thing to consider is that the Pass amps have a relatively low input impedance while the ARC gear has a pretty high output impedance. Though I cant verify this, I had the nagging feeling that my Ref 3 and XA160 was not a good combo because of this mismatch. I have since changed my pre and amp to ones with a higher ratio of output Z and input Z. I am now very happy with the sound though I cant be sure if it is because of the impedances.

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

The LS-26 output impedance (700 balanced, 300 single ended) will have no problem driving the Pass X.5 series which are 22K balanced and 11K single ended.

Listen to the folks at Pass who know their products better than the guessitmators here.

I am using an ARC LS26 with a Pass Labs X250.5 amp and it is a great combination. I also tried the REF3 and that sounds even better, as expected. I tried using the Aesthetix Calypso with the Pass and that was not a good combination. It worked but did not have the magic of of ARC/Pass combination.