Finding myself at an unusual loose end I had the idea to measure the DC voltage present at the wall socket that feeds my equipment.
The DC voltage measured on my true RMS multimeter set on auto range DC volts, was 0.024 volts.
Out of curiosity I turned the microwave oven on and the voltage dropped to 0.016 volts. I obtained the same reading when I switched a hair dryer on.
When I measured the voltage on the output of my DC blocker it was 0.060 volts.
When I turned the DC blocker off the reading was -0.054 volts.
Conclusion, I have no idea. Other than to my simplistic mind I have no need of a DC Blocker.
I purchased one as the transformers where humming quite loudly for several months, but it has just dawned on me the humming had stopped.
Yes, it’s not actually DC.
(in simplistic terms) it’s the voltage difference between the 2 halves of an unbalanced (asymmetrical) full (360 degree) AC sine wave.
The problem with a multimeter is, because it’s a sine wave offset, not actual DC current, a multimeter can only really indicate it’s presence not it’s value. A multimeter has a preset range of sampling frequencies (cheaper ones might even be fixed at one) so the margin for error in measuring something they simply aren’t designed to measure is enormous.
Don’t go sticking an oscilloscope on your mains either! If you don’t have high voltage isolating probes, that can be lethal. It will certainly destroy the scope.
Screenshots from my cheepo hand held scope.
The sinewave is flat topped, probably my neighbours PV cells.
The rms is shown as 223 volts but when measured with a true RMS mm it is 240 volts.
The sinewave does not poluted to my eye sight.
I will park the idea of a DC blocker for the slight hum on the transformers in the Naim gear.
I can’t really see on that screen without a scale. I might not be used to that layout being different from my screen. But you’d see offset if it exists as asymmetrical amplitude. Like +120v over -110v to give 230v (which would be a massive exaggeration).
