How do i get rid of electrical hum in my recording set-up?

I think of this story now when thinking about wiring, tragic. This was a government owned house and was very new and inspected. Just to explain how things can go wrong.

Don't assume things are right, the noise could be a warning things are not right. Even a simple plug in tester like the one below can save a life, I carry one for when I am setting up live shows to check the power points.


Alan.

Martindale-CP501-checker-plug2.jpg
 
All right seeing we are looking at all kinds of causes, I had an induced noise from a power pac plugged into the back of a piggy back plug (or double adaptor) the item with the power pac was fine but the other piece of gear, in this case a Yamaha SPX90, suddenly started to hum and have noise problems.

I also had problems in one of my early studios with the telephone exchange across the road, I was getting induced noise into the mains supply cables, this was extremely hard to get rid off and the only way was to use very good quality cables. It caused real problems whenever a single coil guitar turned up as that picked up the airborne stuff.

Just pointed this out as there is sometimes no simple answer and investigation is needed.

Go back to my answer #8 where I asked if the power point had a good earth, don't assume it does, even the house earth may be bad or non-existent. I did move into a house years ago where someone had broken the main earth cable through the roof between the main switchboard and the main earth point, just left it and did not fix it, a deadly trap for some poor person later. Fixed that and put down a better earth stake and all noise including the stereo in the lounge went away. Check the earth resistance in the house!

Alan.

Very true. In homes these days, we can't assume anything is done to code. Home owners can be the cause of doing something incorrectly, because they didn't want to call in an electrician, because of the cost. Some also assume they can do just as good a job. But, I've seen cutting corners in places that will make you scratch your head. I was asked to install a new light switch in my sister's front bathroom.

I first had to check to see which breaker the switch was on. Her box wasn't even marked. We fixed that issue. Then, I found that that switch had not one, but TWO hot wires coming to it, so if you cut the breaker it was suppose to be on, there was still electricity going to the switch. It wasn't going through the switch, but just sort of pathed into the wiring behind it. That was so strange to find.

Her house was the show house for the area houses, when they were all new. The contractor lived in her house, while he was building all of the others. Being the first one finished, maybe he learned how to do some things with that house. There were other troubling things in there, too.

Her living room was a very high cathedral type ceiling with beams and decorative wooden slats. She got a new roof put on, after a hail storm. They didn't remove the old roof, but just used longer nails to put on the new roof. That's when she noticed that the nails were going through this decorative wooden slats of her ceiling. She had lived in that house for many years and just then she found out there was no insulation in the ceiling of that room and the thickness of the roof there was less than 2 inches. Talk about cutting corners!

So never assume someone else did their job. You could have earth ground wires in your outlets and they could be connected as they should be in the outlet itself. But, if they aren't properly grounded, they are just a mess of green wires going nowhere.
 
Ironically, Martindale had to do a recall on a similar product here in the UK when a few were found to be potentially (no pun intended) dangerous.

I'm not actually sold on the concept that mains wiring is actually the culprit here - my experience suggests that some pieces of equipment have simply awful switch mode PSUs that generate harmonics that decent grounding actually spreads around, plus fear too many devices using the mains circuits to provide communications and internet services using multiplexed data and audio on the mains waveform. Our mains power used to be clean at the point of entry and now it's far dirtier than in the past 50 years or so.
 
The 'yellow' American tester shown above gave me some erroneous indications a while back when I checking some circuits. It is designed with neon lamps and resistors and seems susceptible to capacitively coupled AC and it was showing partially lit lights for a circuit that had an open, but had some AC coupled to it from an adjacent leg. Most times that tester works good, but this was an odd problem.
I bought a solid state tester which has seemed more reliable in identifying wiring problems and it wasn't much more in cost than the yellow type......
Tacklife EST01 Advanced GFCI Outlet Tester
 
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