SBT, Nait and 50Hz hum

[Nickargenta]

So recently I've started getting 50Hz hum through my Nait 5 when my SBT is connected. The hum is independent of the volume control and hasn't got any worse since it started. It's a low enough level that I can turn the volume up a bit higher than normal and still enjoy my music, but the fact that the system was fine previously concerns me a bit. The SBT is using the analogue outputs.

Here's what I've tried so far:

1. Swapping the SBT to a different input on the amp makes no difference.

2. Swapping the interconnect to a different one makes no difference.

3. Swapping to a different power outlet makes no difference (though I suspect it is on the same spur anyway - I have limited options here).

4. The hum is present when all other sources are disconnected.

5. The hum isn't there when all other sources are connected and the SBT is taken out the system.

6. Plugging the SBT into a mate's system (Cambridge something) there's no hum.

7. The SBT is fine standalone through a pair of headphones.

I haven't got an external DAC I can try between the SBT and the Nait.

The fact that the SBT is fine through my mate's amp suggests that it's the Nait at fault, but why doesn't it happen with any other source? Noisy SMPS? What am I missing?

 

[idem]

Analyse what did you change in your house prior to getting hum from amplifier - it could be new fridge, etc, something that is always switched on, then switch it off and see... Some people leave TV on standby, others leave phone charger plugged in and socket on, so it could be anything electrical. I found that heater control gizmo can give hum in my house - nothing I can do about it in the winter...
Best of luck in finding it.

 

[JTC]

I've not experienced this myself with Nait 2 and SBT, so there's no incompatibility there. Could be a degree of DC on your incoming mains?

 

[AussiePete]

I had this same problem with a Nait2 and nothing would solve it until I made up a lead with just the ground pin of an RF coax plug connected, and plugged it into the aerial out of the STB (seeing as my connection to the tv is component) and connected the other end to the Nait earth post. Now it's as quiet as a mouse.
I hope this helps,
Pete

 

[lennyw]

Is it connected via ethernet or wifi?

I had this problem caused by (I think) poor earthing on the ethernet. I wired the spare port on the ethernet to the phono-earth of the nait3 which got rid of it.

 

[Nickargenta]

Thanks for the responses. I should have added that there've been no new appliances arrive or old ones depart. Switching them all off individually has had no effect either.

The SBT is connected via wi-fi so that's not it either.

Not sure what aerial out you're referring to Pete.

In any case, the Nait is sufficiently old that it might be worth getting it serviced anyway.

 

[hifi-dog]

i have a similiar issue with the wall wart feeding my rega tt psu - it makes trannies buzz at times, guess its the whole switched mode psu's thang....