Mains filter

Posted by: HansW on 15 September 2003

The transformers in my Naim power amps and power supplies emit an annoying amount of humm.

I have understood that this may, at least in part, be caused by computers, fridges etc polluting the mains. Rather than filtering the mains for the Naim system I would like to try to put some kind og filter on the mains for the PC's etc.

Looking/asking around in a couple of stores for a suitable product, the only thing I have found is surge/spike protection devices.

Will these do the trick?

Is there another, preferably cheap, product I should look out for (isn't it really only some kind of low-pass filter I need)?

Is this a bad idea all together?

Any help or suggestions would be helpfull.


Best regards
Posted on: 15 September 2003 by Tuan
before you go off and start buying filters, try power down all electrical equipment except the Naim gear and identify which equipment cause the humming from the Naim amp (or power supply). This will tell you how many filters do you need and if the problem can be cured this way. I do have this problem sometime but it goes away (depending on how badly poluted the electrical supply is) by itself without changing anything at all. The best way is to have a dedicated line for your HiFi (a dedicated line runs from the master switch box to the room where the hifi is located).
Posted on: 15 September 2003 by Mr_Sukebe
Hans,

Do you have anything but a CD player attached to your Naim amp? If so, try unplugging it and see what happens.

In addition, I found that connecting up a sub via high level outputs created hum on my amp.
Posted on: 15 September 2003 by Jo Sharp
Try a search for transformer hum - this has been covered before.

One theory is that toroidal transformers are susceptible to a DC component on the mains - this can be removed by using a large isolating transformer but they are not cheap at the VA rating needed for power amps.

The problems might also be caused by machinery/equipment elsewhere in your neighbourhood.... does it go away in the evening when local factories or offices have closed down? Not much can be done about this sadly.

Jo
Posted on: 16 September 2003 by HansW
You are right Tuan, it is a good idea to confirm what the problem is before solving it. I will take your advice.

Mr Sukabe, plugging and unplugging 5the LP12 doesn´t have any effect on thr problem.

Fredrik and Jo, I have already installed a seperate spur which hasn't helped significantly.

Hans