Transformer Hum, how to reduce this

I know the older amps can be a bit noisier but I wondered if there are any tweaks to reduce this ? I dont want to hinder performance with any DC blocking etc. But part of the problem is I have a lot of transformers buzzing away, be great if I could reduce this a little in some way. Any advice and ideas ?

Section in the FAQs should assist.
Try a forum search.

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Turn everything else off in your house (not forgetting things like fridges). Does the humming direct from the boxes reduce very significantly? if yes then turn on one by one, and if the humming increases you have found a culprit. Turn it off and continue turning things on in case more than one. If the humming sometimes suddenly increases or decreases in loudness it is probably DC on the mains, and if not something in your house it would be beyond your control to fix, in which case this:

I think most people report no adverse effect, assuming done properly.

Otherwise I think there’s something in the forum FAQs.

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Deleted, please remove.

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I had mains induced hum here in France. I now have an ATL dc blocker on both my main and study system. Stopped the hum and doesn’t impair sound quality.

Yes thanks I have read this. I will look at a few blockers and try, The other items ‘on’ is a good check but most are 3 floors below

How far below (or above) doesn’t has no relevance: their potential effect on the mains electricity is the same unless your hifi wiring is completely isolated - for which a separate consumer unit might help, though not with cetainty,

IB is as usual right. If this is about your mighty av system, I’d have a dedicated spur anyhow. Probably the most cost effective upgrade you can get.

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Balance transformer will sort it, and bring a nice up lift in darker backgrounds, etc.

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One thing not mentioned but worth checking out is what is the actual input voltage is at your equipment rack. From experience, in some areas of North America the mains voltage can fluctuate significantly from near brown out (low voltage) to near over voltage (high voltage), particularly in more rural areas as opposed to more urban areas. A heavy duty line conditioner / voltage regulator makes a difference in those situations. When I was in such a situation, the low voltage condition (near brown out, drop in voltage from 120V to as low as 108V) there was a significant and very loud hum from some of the toroidal transformers (namely from a SuperCap) in the system that disappeared completely when “normal” voltage was restored.

If you can, monitor your voltage at the system location to see if there is any relation to transformer hum and voltage to the equipment before spending big bucks on solutions that may not address your issues.

Do you notice increased hum from other appliances in your household?

I’m glad there are no doctors here. There is a lot of prescribing cures without diagnosing illness.

You first need to root cause this. Hum has three main causes:

  • over voltage
  • DC offset
  • faulty windings

Audiophiles tend to instantly go to the DC offset issue with an isolating transformer solution. But DC offset isn’t that common. Whereas significant over voltage is.

Root cause it first. Then decide on the solution.


The SCDR for my Superline starts to hum every now and then. When I finish my session I just power down the whole system until the next day and then it’s gone until next time.

I have thought about swapping my SCDRs to see if that makes any difference. Not likely, but you never know.

Are you saying a Supercap is more sensitive than any of the other PSes? e.g. XPS2, 300PS or Hicap2?

Tried a number of DC blockers to no real effect. My best option so far has been an Airlink Balanced Power Transformer. It’s only the 300PS that really hums, the rest is silent. I was thinking of checking the bolts in this as well on the next teardown for cleaning, I also understand that a rubber pad is available to put under the transformer to cut down vibration.


I suspect the frequency of occurrence of overvoltage depends where people live, some regions/countries maybe having significantly less well controlled supply than others. I’m not sure how common or rare DC offset may be, though DC blockers reportedly stopping the hum suggests it may not uncommonly be the cause where hum is a problem.

However, over- or undervoltage are easy to check nowadays with plug-in meters readily available for monitoring energy use, whereas DC offset is less easy to check, so you’re right, checking at the time of humming (and not humming if it varies) makes every sense as an initial part of diagnosis.

Did you glean anything from your poll of members’ mains voltage?

Voltage here can vary across the three phases (France) Main system right now is at 231.4v. Study on a different phase is at 235.7v.
Both have an ATL DC blocker on and both had transformer hum previously. I am not any kind of electrician so I don’t know how these things work, but they do work here. It may be significant that the hum varied during different times of the day.

I didn’t write the summary yet. But yes, there was a clear lean towards a higher percentage of the users in >=220v countries (as a single group) had issues with hum compared to a lower percentage of users in <=125v countries.

My current hypothesis is that the 115v transformer windings (on the same core as 230v) are more tolerant to overvoltage than the 230v windings. I really need to sit down with it and lay it out though. Not in the next couple weeks though. Too much going on.


Not at all. Out of all the Naim equipment I have owned and currently own, I have only had 3 items that had excessive hum: a CB HiCap, an Olive XPS and most recently a SuperCap (nonDR). The first two, retorquing the transformer bolts solved the problem, the Supercap hummed only at low voltage, outside of the voltage range for normal operation.

A common arrangement in Transformers is for there to be 2 sets of winding on the Primary side, which are connected in Parallel for 115V and in Series for 230V.

I expect Naim’s transformers are like this, but I do not know for certain.

Yes, this is why the fact they share the same core (same transformer, different voltage winding configuration) is important to the theory.

I think we’ll need a few years to see how prevailant reported issues with New Classic are though.