Isolation transformer and Noise filter

Does Naim system need isolation transformer or noise filter or both? Currently I just plug the system into wall socket (~220v, grounded). Anyone has any experience please advise.
Many thanks


I cannot offer any advice but I’m also very interested in purchasing a 1:1 isolating transformer. I imagine a 3kv isolating transformer plugged into the home somewhere will greatly reduce the DC offset problem that causes Naim transformers to hum. Has anybody used such a device?

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Isolating transformers are not uncommon. The preference bing for non filtering ones. But they themselves can take on the hum so best installed on a dedicated circuit located in a garage or basement.

The guidance on devices such as these or filters is pretty straightfoward.

  • If you don’t have an audible problem, don’t use them.
  • If you do have mains problem, don’t blindly get a filter etc. Accurately determine what specific mains issue you have.
  • If it is cost effective for an electrician to address the root cause of the problem, do that rather than using a filter.
  • If you’ve accurately root caused the problem and cannot reasonably address it with an electrician, buy a device, such as a filter or isolating transformer, specific to that problem.

Conditions are rightly frowned on in situations where they aren’t obviously needed. Balanced transformers on the other hand, as long as simple non conditioning, shouldn’t negatively affect anything. But better to get in-line ones rated for the full power of the circuit than small plug-in units. Equitech are well known.


Hi, what do you mean by ‘if you don’t have an audible problem’

I have a mechanical hum from the transformers. Is that what you mean?

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Indeed. A mains problem could manifest in different ways. Physical humming from a transformer or noise from speakers. Really depends.

For a humming transformer, likely to be DC offset and an isolating transformer would fix thst. But they’re expensive and need fitting by an electrician. So first I’d measure the DC offset on your mains to confirm that’s the issue before spending.

Hi, I was under the impression that they just need to be plugged in on the circuit. Obviously I need to do more research.

Incoming and therefore upstream I installed many years ago a mechanical energy stabilizer 220/240 v. Since then never a problem …

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Some types of item can just be plugged in.

But not an isolating transformer. That needs to sit in the circuit not simply on the curcuit.

Again, can’t stress enough, do thorough root cause analysis and then find the solution. A hum is a symptom, not a cause. You don’t buy a solution that claims to fix hum. You buy a solution that fixes the specific cause of your hum.

And what if root cause analysis shows DC on the incoming electrical signal to the house?

This isn’t what I’ve determined but it is my best guess atm. Because I have switched off every other breaker on the fuse board. Disconnected all the plugs and I still have the hum.

If the hum changes tone & volume or is not present at some times per day, then it’s most likely DC offset. If it’s an unchanging constant, then it’s probably the transformer that is naturally humming.

I have my own DC blocking filter, but the traffo’s still all hum to some extent, but only audible in dead quiet.

An electrician can diagnose that for you rather than guessing. A multimeter in DC mode will give an indication but an electrician can give a much better assessment.

If that’s the cause, an isolating transformer on the circuit the hifi lives on would be the way to go. So for example, if the hifi lives on a specific 20A 240v circuit, you’d get a 20A 240v isolating transformer to connect to that and the rest of the circuit to the transformer. There’d be no direct connection between mains coming out of the breaker box and the wall sockets anymore. It is absolutely not a DIY job. They are big. And they themselves often hum (since the effect of DC offset moves from the Naim boxes to the isolating transformer).

Yet again, I stress, get the root cause accurately assessed. If the cause isn’t offset, you’ll have wasted loads of time and money.

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That’s great advice. Thanks

An isolation transformer like that one (used on boats or for medical purpose) could do the job. There is even a version that provides up to 7 kWatts and it is rather small. More then enough for any HiFi system.


There are balanced transformers that can be just plugged into a regular wall socket. They may well stop your Naim boxes from humming. The problem is that this transformer may hum instead (although possibly less loudly), simply transferring the problem to a different box, which may not be a great solution if it needs to be in the same room as the HiFi.
If you’re interested, try contacting Airlink, who make a range of transformers, both plug-in and hard-wired. They’re very helpful guys to deal with.

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Worth taking a look at Airlink Transformers for their range of BPS (Balanced Power Supplies).

We use one of their 5kVA ones to good effect, though they do 1.5-3kVA ones that can be plugged into a domestic wall socket.

For details, do a search on Balanced Power Supplies or BPS, as there are many threads about them.

Best regards, BF

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