3.5mm Cable Hum and Static

[DW1961]

I had two 3.5mm cables bad at the same time.


The first cable was creating static over my speakers when moved slightly. The cable connects the DAC to the AMP's AUX port.  (It wasn't the wire going into the jack itself. I tested for that by immobilizing the jack pin and manipulating only the wire.)

 So I replaced the 3.5mm cable with a new one, and didn't have the static issue. However, when there was no input from the DAC plugged into my amp, I got low frequency humming sound from the speakers.

So, I unplugged the 3.5mm cable from the DAC leaving only the cable itself plugged into the amp, and the hum was still there. When I unplugged the cable from the amp's 3.5mm jack, the hum stopped.

I performed the same tests with a 3rd cable, everything was silent.


What would cause a cable and a cable jack to create static when lightly touch or moved a little or cause hum simply by being plugged in to an amp's 3.5mm AUX port? Is there  any easy way to test cables for that sort of defect?

[JustMeHere]

Sounds like a ground loop.  All of your power for all of your audio gear should come from the same wall outlet.

[Benta]

Sounds more like really cheap, low quality unshielded cables to me.

[DW1961]

Sounds like a ground loop.  All of your power for all of your audio gear should come from the same wall outlet.

It is.

[DW1961]

Sounds more like really cheap, low quality unshielded cables to me.

One of them had no hum, but produced the static when moved a little while plugged into the jack. Maybe the jack pin just wasn't manufactured with the correct tolerances?

How would you go about testing for poor shielding?

[DW1961]

Sounds more like really cheap, low quality unshielded cables to me.

Hey Benta,

I actually had another one of those 3.5mm cables that looked exactly the same as the one that produces that low hum when plugged into the back of my amp's 3.5mm jack. Both came from some audio products. Anyway, this new cable that came with an audio product looked EXACTLY the same as the one that produces hum. Sure enough, I plugged it into my amp's 3.5mm jack, and got the same low hum sound. If the problem were ground loop, then wouldn't it persist no matter what cable? I think these cables are just cheapass bad cables. Other 3.5mm cables I plug in don't make the noise.

[Benta]

If you have an open-end 3.5 mm jack cable hanging out of a amplifier input, you can expect a bit of hum. You'll need to short the open jack to see where the problem is. Wrap some tin foil around the jack to see if it gets better.

[DW1961]

If you have an open-end 3.5 mm jack cable hanging out of a amplifier input, you can expect a bit of hum. You'll need to short the open jack to see where the problem is. Wrap some tin foil around the jack to see if it gets better.

I just tested it. After wrapping the jack pin in foil, it went dead silent.

The problem is that even when plugged into the amp and another device, such as a DAC, it hums.

I just received an Amazon basics 3.5mm cable and plugged in with nothing on the other end, and it produced zero noise. My other 3.5mm cables don't make noise when plugged into the amp with nothing on the other end, either.

Also, when I touch the open end of the noisy cable, while plugged into the amp, the hum get 10x louder. Touching the end of the Amazon Basics 3.5mm cable pin does nothing.

So, what's up with these 2 humming cables that go silent upon grounding the bare pin?

[magic]

Some audio cables use coaxial constructions where the signal wire(s) are hidden inside grounded shield and don't pick up mains electric field in the first place.
Other cables use simple three-wire construction and they do pick up electric fields. Shorting the terminals shunts the picked up signal to ground and kills hum.

If a cable makes noises when moved, it typically means it's broken inside and makes intermittent contact.

[DW1961]

Some audio cables use coaxial constructions where the signal wire(s) are hidden inside grounded shield and don't pick up mains electric field in the first place.
Other cables use simple three-wire construction and they do pick up electric fields. Shorting the terminals shunts the picked up signal to ground and kills hum.

If a cable makes noises when moved, it typically means it's broken inside and makes intermittent contact.

Except when plugged into the amp the hum doesn't go away. Is that just the way the simple three wire cables are?