10 seconds of hum when switching on and off

I’m new to Naim and new to this forum, apologies If I’m covering familiar territory - I have had a search and although a lot of you have experienced hum I can’t find a solution to my problem.

I have a NAC92 and NAP140 (I got the NAP140 yesterday, it looks to be in amazing condition), these are connected using a Naim type third party cable. The NAC is connected to a Sonos Connect with a Naim type third party cable.

With all devices connected, when I switch on power there’s a pop and then about ten seconds of loud hum/fuzz before silence - I can then play music and the system sounds great. When I switch off the system there’s a pop and then another period of hum/fuzz before silence. Oh, also and maybe related, the green illuminated Naim logo on the NAC flickers intermittently and seems to have got dimmer.

So, I’ve tried a few things:
I’ve disconnected the Sonos, there’s still a hum when switching on or off but not as loud.
I’ve disconnected the NAC from the NAP, there’s a very slight hum but this seems okay.

So, I think my problem lies either with the interconnect cables (I can return these and get Naim cables) or with the NAC more difficult to resolve as the item came from eBay.

Am I missing anything? Any advice? Any thoughts?

You should get in contact with a Naim dealer. Most probably your NAPs PSU needs to be services and recapped.

This little pop is quite normal for any component that lacks a Switch-on delay with a relay and maybe in the need of getting the surpressor cap attached to the on-off switch changed. But the intermittend hum and bulbs or background lightning beeing dimmed with not interaction by you indicates a PSU issue that needs to be investigated ans solved by a NAIM service

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My systems do the same and are serviced.

Up to a point, it’s normal when you have a pre-amp being powered by the power amp, particularly when switching off as the pre-amp switches off faster than the main caps in the power amp discharge. However, if you get a loud buzz for longer and longer when switching on it may well indicate that a service is due, or indeed, overdue…

As a third party cable is connecting the 92 and 90, anything could be going on. They should be connected with a Naim Snaic 4.

Very true. I would replace with a proper genuine SNAIC ASAP.

I would concur with HH and Richard on this. Since you are using a Naim power amp to power your Naim preamp (a rather neat arrangement I’ve taken advantage of myself in the past, as it saves a box and, therefore, space), your cable between pre- and power- amps will be handling both signal and power. With a Naim Snaic 4, you know you’d have a cable which is wired correctly to do the job.