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Hi,

I am new to the audio world and having a problem connecting the equipment.

I am trying to connect my laptop via 3.5mm jack to my audio mixer which has a RCA input.

The mixer i have is a Yamaha MG10. I am connecting with a 3.5mm to RCA cable.

The problem is that when I play the audio on my PC, there is a major hum/static in the sound.

Am I using the wrong kind of cable? Do I need an interface to get this working?

Thanks a bunch
 

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My brother in law is doing it with the same cable as you are using and he as no hum issue. I did have some hum issue in the past with 3,5mm jack to rca cable and the cable ended up being defective. I was connecting a PC logitech z-2300 sound system to my TV audio out. That was like 8-9 years ago. Once I got a better cable I had no more issue.

Can you try your cable with other component to see if you still have hum? Just fyi my cable was doing a really loud hum/popping noise when I was pushing on the tips of the 3,5mm jack connector with my thumb like if it was internally shorting. Maybe you can try this with yours.
 

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The hum is usually the cause of a ground loop and is very common with PCs. Is the PC and the mixer plugged into the same power outlet? Sadly many PCs use cheep parts for the audio side of things and noise is a side effect. You usually wont hear it with headphones but once you attach it to an external power source like a mixer or even PC speakers this will be amplified.
 

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Try running an extension cord to the mixer so that its fed from the same outlet. Another fix can be to remove the ground from one or the other however this is not a safe practice and is not ideal.
 

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The problem is (most likely) electrical noise from the laptop's psu (power supply).

This is a very common problem. I encounter it quite a lot from people plugging laptops into audio mixers. As mentioned above, it is a type of ground-loop problem, but it is caused by the psu creating noise on its output relative to ground. Plug it into something else that has a ground connection and the noise voltage flows as noise current through the cable screen, inducing and here directly adding noise to your audio feed.

The simple way to check this is to run your laptop with no psu plugged-in. If the noise disappears, then it is created by the psu's switch-mode circuits. The easy way for us to stop this is to run the signal through a pair of balancers or DI-boxes (direct-injection -a multi-purpose box for dc and earth-loop isolation, impedance matching, level attenuation, etc), but good ones are about £110 each. The easy way for you is to either run the laptop off battery-only, or to go to Radio Shack and get a class2 laptop PSU (usually multi-voltage, multi-connector). The class 2 bit means it is "double-insulated" and electrically isolated from the mains supply.

In a class1 psu it needs to be connected to ground for safety -and the noise is then given a reference point, an anchor if you like and a leverge point to create its interference from. It's like the birds on the overhead cables not being electrocuted because they are not grounded either. A class 2 psu has safer design and construction to remove the need for a ground connection, look for the "square-inside-a-square" symbol and you'll know it won't cause the inteference. Incidentally, anything grounding the laptops ground-plane (including some USB devices) can cause this problem.

If you still get noise with the psu removed (and no other USB things plugged in) then you problem might lie elsewhere...


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