From a few away there is an audible hum from my power amplifier, it is not a constant volume, it constantly cycles from barely audible in a gradual crescendo to audible from the listening position then a decrescendo back to barely audible roughly every thirty seconds.
The power amplifier is a NAP200 (non-DR) that is quite old but serviced relatively recently in 2022.
I am about to order an ifi DC Power Blocker but based on what I have described is anyone able to advise whether this is likely interference from the mains or a problem with the amplifier itself?
The analogue out signal cable is several inches away from any power cables, pre & power amp are plugged into a 13A 6 Way Unswitched Socket RFI Filtered PDU but I don’t believe it has any DC blocking or ground loop eliminating capability.
I had a similar experience with my 200 and CB HiCap, both serviced by Class A, so in tip top condition. They both had a rising and falling hum sometimes quite mechanical sounding. We had an electrician in to inspect the house wiring as we rent our small holding and new rules cover this type of inspection, work was done on putting new earths on pipes etc and the report indicated that work has been done on the earthing/grounding of the main fuse box.
To cut a long story short once this had been done we experienced none of the hum that we had before and the 200 and HiCap have remained silent to this day. Supply or mains quality issue perhaps.
It sounds like a case of asymmetric mains, or so called DC on the mains… so a DC blocker will likely help.
If the transformer hum is really loud and sounds clattery it might be transformer needs replacing or checking… but I think that is very unlikely… and most likely the DC blocker is the way to go.
Asymmetric mains can be caused by phase load imbalance at your substation, local transformer, or certain devices in your house that extract load on only one half of the mains cycle with respect to Earth. These can be hairdryers, washing machines, tumble dryers, and similar.
It may be you have poor relatively high impedance wiring and consumer box/fuse board in the house that exacerbates asymmetric loading… but again that feels unlikely, unless very old… and would like result in less than optimal sounding hifi anyway. Do your lights flicker (easier to see with filament bulbs) when you switch on a big load, or switch on a big amp with a large transformer.
So, I have just renovated the house and it has had a complete rewire including meter and consumer unit replacement (the place had lead sheath wiring and spurs everywhere when I moved in). That being said I have not received the electrical safety certificate or anything to indicate the installation has been tested just yet. The upstairs lights does flicker now you mention it but the others do not.
For now I’ll order the DC blocker and chase up the electrician for the electrical installation test & inspection certificate, hopefully there are no faults and the DC blocker removes the hum.
Your replies have just reminded me to check something actually…
edit - there was an earth cable left unattached at one point but I’ve just checked the consumer unit and gave the earthing cables a gentle tug, all seems to be attached fine. There are separate circuit breakers for the mains in each room, garage, lights, heat/smoke/C0 detectors. Sticker on it says it was tested in September 2024 so I’m going to rule out dodgy household wiring for the moment. Although the light flickering is puzzling
I successfully eliminated most of the hum from my system using two ATL DC Blockers. I have one feeding the mains block supplying the Preamps and sources. The other one supplies the 3 250s.
The ATL products are well made and reasonably priced because you buy direct from the maker. I have no connection with ATL other than as a satisfied customer.
@Chaff describes it as …… it is not a constant volume, it constantly cycles from barely audible in a gradual crescendo to audible from the listening position then a decrescendo back to barely audible roughly every thirty seconds.
That is very strange, yes it might be an asymmetric wave form (DC Offset) but the cyclic timing indicates it’s not typical random pollution such as a half wave rectifier on a hairdryer or motor speed control. Something is causing that and it should be traceable, it’s not right and I would be concerned.
As you’ve just had electrical work done, I would ask the electrician to come back and investigate.
DC blocker hasn’t turned up yet however I am more sure now it relates to a mains interference issue.
I noticed the variation in the noise from the amplifier this evening sounded in sync with the electrical whirring I can hear from the kitchen with the amp muted. I assume my AEG dishwasher has an interference capacitor because they are available as spares on the AEG website. My theory now is the sounds from the amp are due to a combination of distortions from my appliances etc. Really hoping the DC blocker does the trick! I’ll post the result.
To my mind it’s always best to solve problems like this at source rather than buying extra hardware to mitigate them further down the line. Power conditioners often take something away from the sound quality as well as just reducing hum etc.
Electrical noise emissions from appliances are regulated by law, so if you tell a manufacturer that their device is causing problem interference with other devices they may agree to repair or replace them: or if out of warranty maybe worth getting it fixed anyway.
Chris, is that relevant for asymmetric mains? Efficient transformers will saturate … therefore buzz. Mains should not be asymeyric.
Sure some manufacturers incorporate DC mains blockers, but for symeyric mains they impact performance, so a third part accessory is surely fine for those affected is surely fine, unless you expect Naim to sell DC blockers.
Well, I am pleased to report this evening it sounds like a win for this little gadget, noise is reduced to the level I have to put my ear against the amp chassis to hear it now.
I agree, it is always better to solve the problem then just mask the symptoms ideally, in the meantime though the ifi DC Blocker + seems have to have done the trick.
Hi, which DC blocker do you think is the best to reduce hum of power supplies and power amp?
something that works fine and does not impact sound
few options, I will put the information I have:
IFI DC blocker (normal or +) is little, nice, but you need 1 per device
ATL
Toroidy (powerful, 1 for the whole system)
Audiolab
thanks!
I can only recommend the DC Blocker+ from my experience fitted to just the offending piece of equipment. I purchased the DC+ to fit to my power amp (it has a higher rating than the DC Blocker). This removed the humming noise emanating from my power amp. The whole system is already plugged into a an audiophile power strip.
I did not fit one to my source (Nac-272) because there was no need, it sounded clean via headphones and the hum came from the power amp itself, even with everything but the power cable disconnected.
I think the general consensus seems to be don’t fit them if you don’t need to, this is to minimize cost and any negative effects on sound quality (I don’t know what those effects are because for me it sounded much better with the hum removed to notice any more subtle changes).
I previously used two of the original iFI DC Blockers on my two NAP 250 power amps that used to hum like they were going out of fashion.
They worked very well and removed virtually all the hum, only being able to hear it with your ear right next to the chassis. The other good point was that it made no difference to the SQ whatsoever.
When I had my XS3, I had transformer hum quite loudly, especially when hairdryers etc were being used.
I got an ATL and it worked brilliantly. Amp dead silent and no SQ issues.
I no longer use Naim amps but still have my ATL in my spares cupboard.
