Noisy electricity supply in music studio (possibly from air-conditioner?)

[sir_sauce]

Hi all,

Thought I'd ask for help in this forum as part of my efforts to get to the bottom of this annoying issue.
I run a small home studio, in a room with a air conditioning unit. Brand is Gree, it uses an inverter and rated at12000 BTU I believe.

Whenever the AC is cooling, it seems to be emitting harmonics into the electricity supply, which can

1) Be heard just by being in the room
2) Be heard clearly through headphone/speaker outputs of some (but not all) of the studio's music equipment

Check out this video describing the problem.

I observed these nasty harmonics to be starting just below 5KHz, and continuing up to 15KHz. Below you can see them showing up in a recording of the noisefloor. I also have a step-down transformer going from 230V to 120V (I am in Malta where the mains voltage is around 230V) which is causing a hum around 50Hz. It's a mild annoyance but much less of an issue than the high end harmonics - those make it nearly impossible to focus and get into the zone.

There is an archived thread on this forum here, where the OP had a similar problem to me which turned out to be caused by inadequate grounding. I've had an electrician come round and check the earthing on my plugs. He found no issues, except that the resistance was just slightly higher than average (~70 Ohms if I recall correctly). Perhaps someone can confirm whether this is OK.

The noise gets even louder when I turn on an analog synthesizer. Not only can the harmonics be heard in headphones/speakers, but they can also be heard when speakers are off and headphones unplugged, like a "phantom" in the electricity supply.

Through testing I have observed some interesting things that could potentially help get to the bottom of this saga... Following a friend's suggestion, I plugged in ALL intruments + equipment + speakers (except air conditioner of course) into the same wall outlet, using multisocket extensions where necessary. His idea was to "avoid any ground loops". I noticed that it significantly reduces the harmonics showing up in the headphones & speakers. If I take the speakers and plug them into a different wall socket, boom - the harmonics are back in the speakers and headphones at full volume. So while I have a way of combatting the noise in speakers and headphones, the "phantom" noise in the electricity supply can still be heard loud and clear, especially when that analog synthelsizer is on.

I'm considering trying a "power conditioner" such as this one, as there are reviews saying it eliminated noise in various scenarios. However, if possible I would like to understand the cause of this issue before throwing money at it. Your thoughts, comments and feedback would be greatly appreciated guys.

Kind regards,
Sir Sauce

 

[sir_sauce]

You should have only one ground rod. If you have one at the generator/solar panel/wind turbine/battery pack and one connected to your home's breaker box, then you'll likely have a ground loop that always maintains a true sine wave and a buzz/hum at 60Hz.

If you have a wide array of noise frequencies that can be caused by an inverter that can't generate a pure sine wave as you load it, then you must deal with harmonics and the filtering built into normal appliances and sound systems can't quite handle filtering the range of frequencies generated and passed through to your audio system.

Lastly, if you have a non-true sine wave from your inverter and multiple grounds, you'll have to address the second ground rod. You should only have one ground rod connected to a bus-bar close to the breaker box and all cables run to the bus-bar (no daisy-chaining of solar panel ground to your back yard outlet and back yard outlet to breaker box - run one wire from the solar panel to the breaker box bus bar).

Quick update from my end - the power conditioner arrived and unfortunately doesn't help my case at all.

In the meantime, electrician has been round and is proposing splitting the circuit on the ground floor (where the studio is) into 3 separate circuits. One for the garage, another for the studio, and one solely for the air conditioner. At the moment these are all being fed from the same circuit. He seems confident separating the circuits as described would eliminate the problem of harmonics coming through the audio equipment whenever the air conditioner is working.

Of course if the problem is due to some kind of radio/electromagnetic interference from the air conditioner then splitting circuits will most likely not do much. But as part of my testing, I had plugged my audio equipment into a power outlet on the 2nd floor (probably on a different circuit than ground floor) using a very long power extension, and the air conditioner noise went away. So I think that confirms the problem is NOT radio/electromagnetic interference. Otherwise, there would have still been noise induced, given the audio equipment had not been physically moved and was still in close proximity to the air conditioner.