200DR - pulsing hum

I have a 200DR power amp (2015 build). It is always left switched on (with the rest of the system). I have phases of listening a lot and then nothing for several weeks, so it has had regular use but I am not making it work every day.

I have noticed that it has started to emit a regular pulsing hum. This is not the usual constant low hum that is often reported - it regularly and continuously pulses on and off with a frequency of around 2 seconds. It is just about audible sitting 3 metres away in a quiet room.

It is difficult to describe and therefore difficult to convey exactly what it sounds like, but any ideas what might be the cause? Perhaps it just needs a service. What is the recommended service interval for a 200DR?

I have not noticed any drop in performance of the system as a whole but that may not be easily discernible if it is a gradual deterioration. But certainly it is all still working and sounding great.

Thanks!

It may be something in your home putting DC on the mains. Have you added anything recently?

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BINGO.

Thank you! Great suggestion.

The culprit is… an electric blanket my wife wanted for Xmas. (Not like you have on a bed - it’s a fleecey blanket you have over you while sitting on the sofa.) It’s made in China and although not cheap £ it seems cheap quality.

My wife loves it so I can’t send it back! So the next question is: would something like that be harming my Naim system (and all other electronics around the house)? Or is it a benign (albeit irritating) side effect?

Thanks again.

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I don’t think it causes SQ issues or damage. It’s the ‘cheap’ way the power is regulated on the electric blanket.

Anyhow, at least you know what the cause is. :slightly_smiling_face:

Electric blankets are notorious for getting the toroidal transformers buzzing away. I don’t think they’ll come to any harm though.

Same goes for hair straighteners.

It’s good to hear that you have been able to diagnose the problem easily.

I would suggest that you conduct a little experiment. I’m guessing that the HiFi is on the same ring circuit as the offending blanket. If so, try running an extension lead from a different circuit, perhaps in the kitchen. Does this reduce or eliminate the noise? If so, it may of course be domestically unacceptable to use this arrangement permanently, but it could indicate that having a dedicated mains circuit installed for the HiFi would solve the problem if you haven’t already done so. It might also give you a bit of a sound quality uplift for a relatively small (in Naim terms) cost.

What’s wrong with a good old-fashioned hot water bottle? :stuck_out_tongue:

Some of us haven’t got enough left for that.

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