P5 transformer running hums sometime


The transformer of the P5 I am running produces hum occasionally and I could not find out why. Especially, when my centralized heater is running the same time with P5, I can hear the hum right away.

All the measurements are quite the same as when heater is not running.The P5 readings: 240V, load 30%, 280-300 watts; thd in 1.6-1.8%; thd out 0.1%. Running single sin wave.

Has anyone encountered the same situation? Any idea to reduce the hum? Thank you. I moved it a bit but cannot get rid of the hum. This does not happen often but when heater on, it tends to be quite often. So far my solution is if music on, no heater nor aircon. If aircon/heater then no music cry



That’s probably because of DC on the line. When something like your heater kicks in it can unbalance the transformer going into the home and that can cause DC. Fortunately, the output of the P5 will block DC from going to your equipment so your equipment won’t hum. But still, the P5 has a transformer of its own that can under those circumstances.


Thank you very much, Paul. Just add some information in case:

  • I tested with the heater. I switched on the heater and after 1 minute, P5 started to hum. After 5 mins, I switched the heater off and the hum was gone. When heater on: in 236.2, out 239.9; thd 2.2%, power 293w, current 1.65A, thd out: 0.1%, load 32%, freq: 50hz

When heater off: in 240.4, out 240.2, thd in 2.1%, power 294w, current 1.65A, thd out: 0.1%, load 33%, freq: 50.0 hz.