Ahhh. okay.
Just for chuckles and grins ... Measure the AC mains with your DVM on DC volts. A variac shouldn't hum or growl unless your current approaches or exceeds the maximum rating. Not the old ones anyway. I've seen some new ones that are rated for intermittent duty, smaller cores. That means they are rated much lower continuous. We used to buy them for their continuous ratings.
Just for chuckles and grins ... Measure the AC mains with your DVM on DC volts. A variac shouldn't hum or growl unless your current approaches or exceeds the maximum rating. Not the old ones anyway. I've seen some new ones that are rated for intermittent duty, smaller cores. That means they are rated much lower continuous. We used to buy them for their continuous ratings.
It hums while idling also. Not loud but noticable and it does not change with a load. It's brand new. Uniteck STG-1000W. Probably chinese, build quality is good but nevertheless it hums...
Again a link to good guy in Australia : https://sound-au.com/articles/xfmr-dc.htm
There he explains all in details including safety percussion, so no need to repeat, you can search here on same subject too. Just be aware that DC in mains might appear and disappear , but if this is the root cause, hum will do the same.
I know this guy, very good information, just read it. I understand now that a small DC voltage can create saturation, mainly in bigger torrodial trannies and cause problems. Indeed I have experienced it once in a while, this intermittent temporary hum from a transformer and I understand now how that is possible. Good read.
Hum in my variac is not intermittent, so I doubt DC is the cause -only if DC voltage would be permanent. I suspect that the variac transformer itself has some loose laminations or whatever that buzzes. I will not build a DC blocker, by the way, but instead I am more leaning towards using my off-grid system strictly for audio again, as stated in previous posts. I have to install some additional wiring across the home but that is no hassle. The inverter has it's own safety features and circuit breaker as well as earthing, so it is safe anyway. I went this route before and it sounded a little better as well and should be able to listen for >10 hours until the batteries have to be recharged (solar power or charger via mains) and during daytime when the sun shines even longer.
Then you are fully isolated from household mains and no voltage swings anymore and no humming variac... and possibly even saving the earth (grin).
Hum in my variac is not intermittent, so I doubt DC is the cause -only if DC voltage would be permanent. I suspect that the variac transformer itself has some loose laminations or whatever that buzzes. I will not build a DC blocker, by the way, but instead I am more leaning towards using my off-grid system strictly for audio again, as stated in previous posts. I have to install some additional wiring across the home but that is no hassle. The inverter has it's own safety features and circuit breaker as well as earthing, so it is safe anyway. I went this route before and it sounded a little better as well and should be able to listen for >10 hours until the batteries have to be recharged (solar power or charger via mains) and during daytime when the sun shines even longer.
Then you are fully isolated from household mains and no voltage swings anymore and no humming variac... and possibly even saving the earth (grin).
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Sounds like a plan.
You can consider extra HF filter after inverter, built in ones are just good to meet code. Inverter will eliminate overvoltage and DC issues, but brings in switching noise...
You can consider extra HF filter after inverter, built in ones are just good to meet code. Inverter will eliminate overvoltage and DC issues, but brings in switching noise...