If you been on this Forum for a while, you will know there are several reasons for a Naim Power Supply or Amp humming. Here is my story on one particular possible reason.
I’d noticed a Hum on my HiCap and to a lesser extent on my NAP 140 when they came back from service. I couldn’t be sure if it was down to the service, or the fact that I have only recently been focusing on the HiFi since retirement.
Anyway, after reading many articles on the Forum, and eliminating other items on the Ring Main potentially causing this, I came across a possible reason as being Over Voltage, which as the phrase would indicate, the Voltage levels are too high. Now in the UK, the Voltage to your house should be 230V with a tolerance of -6% +10%, giving an upper limit of 253V. A typical supply will vary in voltage throughout the day, and will be at its highest when the substation load is at its lowest, but should never go outside the defined tolerances.
Using a multimeter, I measured 254V in my house. I was then able to look at one of the sets of data from my Solar panels, and I was able to see that during daylight, I was averaging 255Volts. I could also look at stats from a year ago, and saw the same high figures, so it has probably been too high for a while.
I logged a ticket with my Electricity Suppliers, and they said they would be out within 3 hours. To my amazement they were, and confirmed a 254V measurement at my local Substation. Two of them worked in the substation, and found that the substation tapping was set to 4, which was not the standard of 3. They temporarily dropped the voltage to 240V and I noticed a big improvement in the Hum which would have been perfectly acceptable. The graph below shows what happened to the Voltage when they first dropped it. Unfortunately when they completed the work, the hum was mostly back, with a voltage of around 249V.
Over the following days, I monitored it, and it was now averaging 249V with a few instances of just over 253V. Armed with this, I thought I’d try them again as they were so helpful. Again they came out within 3 hours. This next phase took a little longer, but they did remain helpful. To help eliminate, or point the finger at my Solar Panels, they placed a recording meter in my Meter Box, and another in the substation for a couple of weeks. Some of those days, I would turn the Solar Panels off to help diagnostics. Thankfully they found that the values at my house was in line with that at the substation, helping to eliminate the Solar Panels as a cause, and put the focus back on them.
They now had three ways they could fix this:
- Add more load onto the secondary (my local) substation, thereby dropping the voltage overall.
- They could also drop the tappings on the local secondary substation further. Of course if they drop the Voltage, they then need to ensure that the house furthest from the substation doesn’t then get an Under Voltage.
- Bypass the local substation completely, and feed from one serving more households
First they went for option 1) as that was easiest to implement, but this still left peaks above 253V. Finally they went for option 3, which now results in an average of 245Volts. They may revise this at a later date.
(Graph shows the average 249V average then finally coming down to 245V when they implemented option 3)
The all important question, how’s the hum? We…ll, all I can say is that it’s better, but not as good as I would ideally like, so not too surprisingly there may be more than one reason for this particular hum. It must be said that Over Voltage is not a common Hum reason, but I thought worth documenting for others out there.