I’ll be connecting up a second 555PSDR to my ND555 today and wonder if a particular switch-on sequence is recommended?
Thanks
Graeme
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Apparently not. I switch on analogue first when I remember - but it doesn’t seem to make any difference when I don’t.
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I just switch either on/off within a second or two of each other.
When switching off it does not matter at all the sequence if it is done with a small interval as the latency of these large linear supplies discharging means they are ‘on’ for several seconds anyway when powered-off.
When switching on it is obviously different and it is difficult to call what would work best for optimal safety but I think it does not matter much if you turn them on couple of seconds apart.
I don’t power them together or any Naim item as it can cause a large current spike that is not a good idea and had on the odd occasion when I did it trip my mains circuit, even though it should not, but phase angles at high current can be interpreted by sensors as a problem.
So just power them both on/off close in sequence an it will be fine - in my exprience so far!
DB.
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Would it be possible to stack two PSUs on top of each other? I can‘t place them on separate levels, so stacking would be the only option. Do you dedicate a shelf level for any of the two?
I have separate shelves for each and have also spaced them apart so that the digital one is next to the “noisier” 500 power supply, while the analogue one is next to the fussier 552 PS.
I space mine by a medium level - I heard it as better than a standard level and worth the Fraim cost.
Space can be an issue so not for everyone, just reporting that you can hear it - the bass becomes more open and better defined if you can have a little more space between the two supplies.
Two supplies stacked, if you have to do that, will still be a lot better than one supply - to avoid scuffing by feet put small black bits of paper under the feet or the top PS. 
I have my ND555 on its own Fraim stack alone as I found it improves things a lot - again this takes-up space and Fraim cost but just for information know that there is a lot more to be had from the ND555 source if you have the opportunity ahead to provide more space. Lots more detail resolution and a faster sound that I liked enough not to do without and the extra Fraim costs were a fraction of the second supply cost so I decided to swallow that and have it optimal for my system.
If you run it into an Active system I’d strongly recommend these details - borrow Fraim from Dealer and try then it makes it easier to understand.
But it works fine in a more compact installation - that is how most people hear it demonstrated - but there is more to be had! 
DB.
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As above. No sequence.
Yesterday I powered up my system, one component at a time, after a few days of thunderstorms, and the digital feed 555PS-DR surged and blew a fuse. The first time this has happened in many years of 555PS usage. Happily, it blew the fuse in the PL from the wall into my Musicworks block, so it was much easier to change than all than fiddling about with case fuses.
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I wondered that…thanks for asking
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