The story starts about eight months ago, when I noticed that my Naim NAP 250 power amplifiers were beginning to hum. Did some research on this and identified that it was a mechanical hum and not a ground loop hum, no hum coming from the speakers.
It started to get worse and you could hear the hum when sitting down when not being used despite having a decided mains supply to the hi-fi system. I put this down to the mains coming into the house as around us, we have a significant amount of civil engineering going on around us due to new railway infrastructure. Where I live, we have four compounds for the new East West Rail line and within four miles there is a massive compound for the High Speed 2 rail line, plus numerous others in the vicinity. It will be nice when all is completed, I must admit.
Not only is this bringing traffic disruption and increased traffic with associated noise and dirt, but we are experiencing some utility issues. Damaged water mains from the heavy lorries, occasional power cuts, cable strikes to the fibre optic broadband system, etc.
Taking a gamble that it is all the work going on around us causing the issue, I thought that I would try a DC blocker to see if it improves the situation. If not, it can always be returned and then the next step would be to get the amplifiers looked at.
Decided to try the IFI DC Blocker as it is simply installed in line, rather than having another box and additional mains cables, so ordered one to try. It is quite a neat and compact unit.
It has been installed for a couple of days now. I put it on the noisiest 250 and immediately, the hum was reduced. Didn’t cut it out totally, but reduced it so much, that you can’t hear it unless you put your ear right next to the amplifier. The other 250 is still slightly humming, but that was never as bad as the first one, so now I know that it works, I’ll get a second one. The SuperCap, FlatCap and the NAPSCs are all quiet.
As mentioned, it’s been in a couple of days now and there is no apparent detrimental effect to the sound quality, which is a nice relief. One additional benefit I’ve noticed, is that the 250 with the DC Blocker is running a bit cooler than previously. Because my system is powered 24/7, there was always a slight bit of warmth to it if you felt the case, with the noisy one being slightly warmer. Now that one is cooler than the other 250 and I wasn’t expecting that.
Im hoping that this is only a temporary issue and the mains will settle down eventually, when all the work has been done, but this will be a few years yet. Our section is due to be completed by the end of 2023, but the whole line is scheduled to be completed by the end of the decade. However, at the moment the line is not going to be electrified, but could be in the future, that will then bring further issues if they decide to do so.
I will let you know how I get on when the second IFI DC Blocker arrives and has been in use for while.