Subwoofer hum when using expensive cable

[Gundud]

Hi!

My subwoofer (PB 2000 Pro ) is connected to Minidsp.

So far I have tested 3 cables:

1. Diy cable with all the expensive material = hum.
2. Ready to use cable $5 (Vention/Ugreen) = hum.
3. Cheap $2 RCA cable (5 meters) with very thick rubber = no hum.

The thing is, the cheap RCA is uggly, its blue and thick and its dual rca, so i dont use the other connector.

Can somebody educate me on what would be the difference from this 3 cable that cause hum? The hum is quite loud.

 

[Doodski]

Hi!

My subwoofer (PB 2000 Pro ) is connected to Minidsp.

So far I have tested 3 cables:

1. Diy cable with all the expensive material = hum.
2. Ready to use cable $5 (Vention/Ugreen) = hum.
3. Cheap $2 RCA cable (5 meters) with very thick rubber = no hum.

The thing is, the cheap RCA is uggly, its blue and thick and its dual rca, so i dont use the other connector.

Can somebody educate me on what would be the difference from this 3 cable that cause hum? The hum is quite loud.

It appears you may have 2 bad cables. Do you have a multimeter to measure them and determine if any are, "open?"

 

[Cars-N-Cans]

I would also check the resistance of the shield as well. Put one lead on each of the outer shield conductors at each end of the cable and measure the resistance. If its more than about 0.5 ohms from end-to-end then fields around the wires can start to introduce hum on the shield conductor. Also if there are any breaks in the shielding or its something cheap like just a few strands of copper going around the center conductor that will do it as well. Since RCA's are unbalanced, any sort of voltage differences along the cable will be amplified along with the signal (e.g. hum and the like). It could also be do to a ground loop as well if there is substantial current circulating, it can introduce hum from the voltage drop along the shield conductor. But see what the shield ohms out to be in the cables that don't work to see if there are any immediate clues there.

 

[Speedskater]

Most budget DMM/Ohm meters do poorly at resistances of less than 1 Ohm. So touch the two probes together. Note the value. The end-to-end shield value should be only slightly greater than that value.

 

[Spkrdctr]

As a non-answer to your post, I recommend the cheapest wire you can find. Seems you system does not like fancy stuff. Might be a beer system instead of a champaign system. Ok, I will let myself out now.......

 

[DonH56]

I wonder if the ground is broken in the cheap cable... Ground loops can be tricky; sometimes, the lowest-resistance cable causes worse hum, where the cheap cable's higher resistance is just enough to prevent a loop, but in this case like the others I suspect a problem with the other cables (or connection when plugging them in).

 

[wwenze]

With RCA you can easily disconnect the ground leaving just the signal, that gives you some ideas for testing.

 

[Gundud]

I wonder if the ground is broken in the cheap cable... Ground loops can be tricky; sometimes, the lowest-resistance cable causes worse hum, where the cheap cable's higher resistance is just enough to prevent a loop, but in this case like the others I suspect a problem with the other cables (or connection when plugging them in).

This is what I suspected too. My initial thought is there is no grounding on the cheap cable. I don't want to cut it open since this is currently my no-hum cable, but the other cable have 3 wire inside, I suspect the super cheap one only have 2?

 

[Gundud]

It appears you may have 2 bad cables. Do you have a multimeter to measure them and determine if any are, "open?"

I do have multimeter but the cheap one. What do you mean with open? If its continuity then the multimeter beep and showing 002 value.

Most budget DMM/Ohm meters do poorly at resistances of less than 1 Ohm. So touch the two probes together. Note the value. The end-to-end shield value should be only slightly greater than that value.

Touching the two probe together, resistances is 02.7 (selector is on 200, other selector value are 2k, 20k, 200k, 2M, 200M). The cable core resistances is 04.2 (on 200 selector)