Pulsing phono boards

Hi everyone

Ive just fitted a pair of 323/5 phono boards to my Nac72 in the slots connected to the bnc phono inputs. They’re not connected to a turntable yet just sat in the slots’ but when I turned on the 72/140 the speakers started pulsing. Not nice.

Do I remember something about link wires having to be cut or connected or is that nothing to do with the problem?

Many thanks for looking.


Motor boating would indicate that you have a NAC72 that still has the link wires intact on the phono/aux input.


Thank you Richard

I take it they are the 2 wires on the base pcb and that they need cutting?

Also, could you suggest how I connect the RCA leads from my Rega Planar 6 to the BNC connectors on the 72?


Here’s the official advice sheet from Naim on this.


Your Rega is best fitted with BNC plugs. However 50ohm adapters will get you up and running temporarily.


So ideally cut the rca plugs of the rega leads and replace them with bnc items?. I make cables at work so this would be OK for me to do as long as I had some kind of diagram/pinout for them?

Many thanks for the advice.


Simple. BNC’s are quite similar to Phono’s. Core of the wire to the pin, screen to outer.

Something like this…

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Thanks Ian

How do you know which one is chanel 1 and 2?


Ah… Naim meets the real world… lols.

Are your Rega leads ID’ed in any way…? Red is almost always the Right channel. So plug the Red lead into which ever Channel your Right Hand speaker is connected to - which is … usually Naim Channel 2… Simples… :grin:

PS. You have fitted 323 boards - which are designed for Low Output Moving Coils carts - ?

Thanks for the info Ian. Yes I have a rega ania, which I think is right for the 323 boards. They didn’t have an ident as to whether they were S or K though. Just 323/5 printed on the boards.


The resistor value gives it away as to whether they’re K (560 ohms) or S (470 ohms).

Thanks Richard

Should I aim for 75 ohm bnc conectors with the RG179 size for the cable?

You’ll need 50 ohm BNCs.

Be careful before you go removing the RCA’s. You need to check the construction of the cable. It may not have a braided shield, the conductors might not be copper.

I have a turntable with Van Den Hul D502 tone arm cable, no braiding and the conductors are Silver and Linear Structured Carbon.

I’m usually pretty gung-ho when it comes to getting out the soldering iron, but the Tiffany RCA’s are not going anywhere. :innocent:

It’s a good point; not all interconnects can take BNCs easily. I don’t know about the Rega ones.

Alternatively you could ask Naim or your Naim dealer to convert one of the BNC equipped inputs on your NAC72 to RCA phonos.

On my own Rega RP10 I left the locking RCAs in place and connect them to the WBT Next Gen RCA Phono sockets on the Superline.

Main thing is to avoid having to use adaptors.

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Again, thanks for the input (no pun intended) These things usually start out seeming straight forward and then by increments, get more complex…


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Very true… So many things, follow this pattern… not just Naim HiFi… :face_with_monocle:

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