Preamp output impedance, Amp input impedance and drive ratio? Pass Labs XA25

@chauncey 

As others have mentioned, gain is key- especially with the Pass XA25 because it has a very low 20db gain.  

A higher gain preamp will get the most out of it in terms of sound that has contrast and separation and not just monotone.  

I used the XA25 with my Cary Audio SLP-05 (23db gain) and had amazing results. 

The Cary SLP-98L is a lower cost option that has 20db gain and sweet sounding 6SN7 tubes.  Get yourself some 50’s NOS Sylvania and you’re set.  

As for output impedance, it has 440ohms and the magic ratio is 10:1, so you would want a power amp input impedance of minimum 4400 ohms.  Since the XA25 has 47,000 ohms input impedance you are covered.  

Pick the best sounding preamp. With that input impedance you’re good to go. 

Good call pointing out XA25’s gain - 20dB is a bit on the low side, though perhaps this should be expected to match its lower power output. I know it can push up to ~80 Watts/ch in class AB - but that’s still low-ish for a modern standalone SS amp.

Still, 20dB is sufficient with most active preamps; you’ll just need to get used to pushing the volume dial a bit higher than you would otherwise. With today’s digital sources, most systems have a surplus of gain. However it can be a problem if you have a weak phono stage, or hook up an tape deck with anemic output. 

Some of the lower power tube amps can have relatively high gains (especially some vintage models), which is likely a contributing factor (not the only one) to the old "tubes watts" myth. I had an Eico HF-87, vintage EL34 amp good for 35 Watts/ch, with a whopping gain of 33dB (gain pots at max) - this is more typically what you’d expect with 300+ Watts/ch amps. Of course it used a 12AX7 tube for its input (lots of gain).