On or Off

Official manual:

https://www.passlabs.com/wp-content/uploads/2020/12/XP-22_om.pdf

"Leave it on or turn it off: The product is designed to be left on all the time. The
exception to this might be a case where the preamp will not be used for an extended time - in that case it can be turned off.""

I always left my Pass pre on unless I was was leaving for more then a few days or a chance weather could cause a power outage or surge.

i have a pass amp also.  the manual is not specific about leaving the front panel switch on in addition to the rear switch.  

i do leave the rear switch on but turn off the front panel switch after listening.  

On!

Mike

I reently bought a used Pass Labs XP-17 phono preamp.  It too only has an on/off switch on the back.  I called Pass Labs and was told to leave it on all the time.

On for better sound 

I leave my Pass pre and Ayre phono on but switch off the Pass amp but try to give it at least 30 minutes warmup.

Pass always sounds better off to me. 

🤣

Just a joke people.  Commentary about readers who only read the headline and not the OP.

You have an on/off switch? Wow! My XP-15 phono stage doesn't. The only way to turn it off is to unplug it. I'm guessing it's meant to be left on.