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Mains hum issue


Hi all,

Hope you can assist. I am getting the various bits on a cab I received up and running and am having the following problem....

I wired the cabs LED controller up and it's working fine, but when it's powered on there is a horrible mains hum coming out of the speakers. When it's disconnected, no hum, so the rest of the cab is fine and no earthing issues. I was just wondering why adding a small controller board is causing the hum. The power connector is a simple two wire job.

Cab powers up, monitors and PC in it, plus other non-controller LED lights fine, no hum. Power board up. hum.

I've attached a photo of the controller and the audio amp for ref.

HELP!  :laugh:


Is your audio power supply separate?

Some audiophiles go to great lengths to isolate grounds and remove/avoid interference. If you can power the amp from a separate power brick that will help. You can isolate the audio signal grounds with audio baluns, which often come in pairs.

Those power input wires might be acting as antennas, collecting interference.

Using an AC line filter might help. They are pretty cheap and easy to install on the main power input.

How is the LED controller powered exactly? It is also possible to build a simple USB or low voltage line noise filter with 2-3 capacitors and a ferrite bead. For example,

Again, it might help if you can power the LED controller separately from PC/amp/etc.

Are the LEDs actually connected to the board when you get the hum?  If so then disconnect the LEDs and try again and see if it hums.  The photo looked like you have the LEDs plugged in.  If so they can generate a lot of interference.  The LEDs that you are running without a controller are dumb LEDs and do not have high frequency data being set to them.  I use what we call "smart pixels" in my Christmas show where each pixel has a WS2811 chip.  I believe they run off of 800 kHz data.  Even though my controllers are nowhere near my garage and are on a different circuit I cannot use my garage remote control while my pixels are powered up.  The high frequency data causes interference and the remote stops working.  I'm not the only one in the hobby that's experienced this.  We always get new guys that are asking about it cause their wife is pissed when she can't get the garage to open.  At first we thought it was the cheap Chinese power supplies we were using but switching to quality Meanwell supplies never fixed the issue.

It's likely that by plugging in the LED device you're connecting the chassis of the audio box to the ground somehow. There are some pretty lengthy papers about this in audio land but basically you want a 'ground loop isolator'.
Think of it like this: You have your audio amplifier with a power supply and then an amp circuit. The amp circuit itself should be "floating in mid air" and never connected to the ground. You might notice the humming effect if you sometimes touch your car stereo with your hand and get a bit of a hum or 'better reception'. High quality receivers go to great lengths to insulate the amp from the ground.
You're then connecting that amp to the speakers, which are mounting in a box, floating in mid air, via the +/- speaker wires, who are also floating entirely in mid air.
If you were to connect the speaker chassis to an earth ground and the amp to an earth ground then their respective distance from each other would result in a humming sound equivalent to 'how out of phase' their respective electromagnetic fields were (because you have basically attempted to use the negative speaker wire as both a ground for power and for audio).

In order to avoid this, you can either 1) Make all your components hover in mid air (very difficult to do.) or 2) Make quite certain that there is no grounding connection that is shared between the speakers and the receiver (still very difficult to do, but slightly more attainable).

First thing to try is hook up all the audio by itself and see if there is any discernable humming. If not, plug in the power cord to your LED system with the ground/neutral connected to a different outlet. If the humming stops, then look for a power outlet based ground loop isolator. If it continues, then you likely have some other low voltage ground wire that is interconnecting the two chassis together and you would have to systematically isolate those from each other. There are available some inexpensive ground loop isolators that help with this issue between components so if it turns out that you have an audio interconnect between your LED system and your AMP that is likely your culprit (and the most logical place to insulate the ground). These would put a transformer in line to interrupt the ground.

Thanks guys, some great advice there, will get stuck in!


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