I’ve recently added a TT to my system. I have now have four sources: TT, radio, streamer, and TV. These feed into a 52. Switching between sources before I added the TT was noiseless, now there is loud pop as I change inputs from TT to any of the others.
Can anyone explain this please?
Authentic vinyl. That is the only explanation. Or maybe there is now a load on the phono output so, why not pop!
Has the TT got a separate phono stage amp, or does the cartridge output go direct to the 52? If tge former, tgat is the cause, if not the reason.
You now have an input on your 52 connected & enabled, which is several orders of magnitude more sensitive, than any other. Add another order of magnitude for a Moving Coil cart, vs a Moving Magnet. (You don’t say what your Turntable consists of…?)
Suggest you look carefully at the earthing/grounding of your Turntable… 
Are you turning volume to zero before turning off, and not increasing until turned on? That is good practice, if not obligatory - but whether that will stop the pop if you don’t leave it on I don’t know. The second pop is probably relays switching after a set time. My present amps (not Naim) have relays isolating the speakers to stop pop at switch on, but when they switch all I hear is a feint click.
@Innocent_Bystander its integrated in the 52. I was surprised that my original cards were still up to scratch. Now you mention it, I recall having to turn the volume down when I last used a TT. Interesting about the relays (see below), I am just curious about the source of the pop. Do you know if the newer Naim pre-amps have such relays, or have they solved the pop by other means?
@IanRobertM it’s an LP12 with a AT VM750SH moving magnet cartridge. Your explanation makes sense, I’m just not technically minded enough to put it into words.
Ah… OK. Well, a Moving Magnet (or high output Moving Coil) cart is a bit less… troublesome than a low output Moving Coil.
Your 52 will have 552N boards fitted - same as I have in my 82 (used with a DV10X). And not at all bad they are - also very neat - no extra boxes… 
I would just suggest you turn Volume down a little, before swapping inputs… 
The relays @Innocent_Bystander refers to , I believe , are for stopping the ‘pop’ or ‘bump’ at power on. Not sure that every Naim power amp has them…?? (@Richard.Dane - ?). My 250 has always had a significant pop or bump at power on (and I was told this was normal - but it sems less so, with modern caps fitted) - while my 140 is more … subdued… 
If you disconnect the TT does it stop doing it?
I’ll check once the rugby is over. Certainly there was no pop before I connected the TT.
Ok - once the TT is unplugged there is no thump when changing inputs.
I just have to remember to turn the volume down. But does the thump do any harm, or is it just annoying?
What position do you have the NDS ground switch set to ?
One other thing to mention (slightly related) is do you have a digital output from the TV available. If so it would be worth using the NDS via an optical cable rather going straight from TV to 52.
If very loud it potentially could damage speakers. Otherwise nothing at rusk of damage . Turning down volume or muting before switching removes speaker risk.
Agreed. The thump is to remind you to turn down the Volume… next time…
TT is LP12. It’s tricky to see where the ground switch is set. Too much spaghetti but I did not change its position when I set up the TT.
Ok, its a LP12… with which Arm…? Is there an earth/ground lead - and is it connected to the terminal below the input on your 52…?
It’s an ittok LVII.
Yes the forked / spade earth cable was attached to the 52.
I would be tempted to check and/or clean that connection.
Have you tried to change, on the back of your NDS, the switch « Floating « to « chassis « , or the contrary ?
I also think you should try changing the signal earth switch position.
Thanks for the suggestion @frenchrooster and @Richard.Dane
Sadly, switching between floating and chassis did not solve the issue. But J J Cale sounded good either way.
I’ll just need to remember to turn the volume down.