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Hum from phono input

snaphappybob

snaphappybob

pfm Member
Was about to listen to a record and was unable to due to a loud hum from the right speaker.
I have narrowed it down to either the turntable or the phono input as it does not happen on any other input. Was working fine but just wondered whether anyone has had this issue and how they resolved it.
System comprises Naim Nac52 with phono boards and a project debut carbon turntable. The turntable is very much a secondary source but I would like it to at the very least function.
Suggestions?
Cheers
Rob
 
First thing would be to swap L/R from the TT to phono to show whether it’s the TT or phono at fault.

Obviously turn everything off while doing this.
 
No homeplugs in the house so can’t be that. Just tried swapping the connectors on the turntable and the hum stays on the right side so that narrows it down to the pre amp. I suspect that it is the right channel phono card that is at fault just don’t fancy disassembling the whole system to check the card. Obviously I’ll have to when I get the chance unless there’s any other suggestions.
 
Ok, so it's not the TT or tonearm leads.

May suggest you swap the phono boards over.
  • If it moves channel it's the phono board.
  • If it persists on the right channel it could be the part of the SuperCap which powers the phono boards.
 
Can’t swap the boards over as they are specific to each channel. It’s been fine till a couple of days ago. Bought the phono boards s/h a couple months ago but can’t blame the seller.
 
snaphappybob said:
Can’t swap the boards over as they are specific to each channel. It’s been fine till a couple of days ago. Bought the phono boards s/h a couple months ago but can’t blame the seller.
Click to expand...
The NA522 cards each have four connections to the pre-amp; in, ground, out, and 24V. Suggest reseating the Rch phono card, as a poor ground connection here will be your most likely cause of hum on that input/channel only.

When seating these cards, make certain that all four pins protruding from the NAC PCB are engaged with the corresponding sockets on the phono card before pushing home. When you look at the underside of an NA5xx card, it is easy to imagine two sockets down one end missing the mark, and subsequently 'creeping'.
 
Craig B said:
The NA522 cards each have four connections to the pre-amp; in, ground, out, and 24V. Suggest reseating the Rch phono card, as a poor ground connection here will be your most likely cause of hum on that input/channel only.

When seating these cards, make certain that all four pins protruding from the NAC PCB are engaged with the corresponding sockets on the phono card before pushing home. When you look at the underside of an NA5xx card, it is easy to imagine two sockets down one end missing the mark, and subsequently 'creeping'.
Click to expand...
Hi Craig
When I tried to swap them round I made sure they were properly seated, think ther must be a fault with one of them.
 
snaphappybob said:
Hi Craig
When I tried to swap them round I made sure they were properly seated, think ther must be a fault with one of them.
Click to expand...
Perhaps they are both coming due for a recap then.

According to the boffins on here, it is the tants and the 47uF electrolytics that eventually go off, the rest typically last forever. See here...

Also, as they would be 'under the solder gun' anyway, consider dropping the input loading cap value while you (or someone) are (is) at it, as per MJS's suggestion here...
 
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