Stacking pass labs power units??

Stacking is very bad for sound.

Contact Pass and ask them. They show them stacked on their site, that might just be for the photo op, though.

The control can be placed on top of the power supply but for the best performance
they should be separated a little. Putting the power supply on a lower shelf works great.

From the manual.

...But can you stack two power supplies? 

Two Class A units produce a lot of heat.

Very bad idea.

@chorus the units he is describing are a phono pre and preamp, neither really produces much heat overall. 
 

To the OP, it should be ok to stack the power supplies. But keep them away from the other units. I would keep the phono pre as far from everything as possible. Having said that, stacking the two pre’s won’t hurt anything, but you might find a bit of noise possibly. 

Thanks for the replies and instruction. I'll do as builder3 suggested, and just call Pass on Monday to see what they say.  Thanks again, everyone. 

Why not just try it see for yourself?

True.  I will try it, but wanted other thoughts and will see what pass says.

Will you be running both preamps at the same time?

If not, then I see no problem.

B

The folks at Pass said it was no problem to stack the power supply chassis together and then separately stack the two preamps. So I did this, but found that the two preamps stacked together produces more heat than I'm comfortable with. (not that they were too hot to touch, so I'm not suggesting there was overheating going on, but they were in a middle shelf of a rack and therefore, even though they were "breathing" there was still a roof over their head and warmer than my liking) So they are stacked back on their respective power supplies. I just don't have any extra space to put four separate chassis. Pass gear is designed to stay on all the time and therefore they would be running at the same time.