how to stop speakers from humming

[deoblo85]

I biult a jukebox and powered with a amp but im getting a humming noise from my speakers and all my plugs are hooked up right.The more i turn the speakers up the more they hum can any one help

[BobA]

There could be several sources for the hum.   

1. What are you using to power your amp?   Is it good clean power source?   Does it have adequate capacity?

2. Do you have a single ground point for your audio system?   Ground loops or poor grounds can cause a hum.

What type of amp and speakers are you using and what are you using to power them?

[deoblo85]

The power supply is good what would be the proper way to ground it its in a wood cabinet ive never had this problem be for.Is there something i can buy to correct this problem i put the same amp in my other jukebox and there's no hum.It's a crown 402 amp with 12"yamaha speakers.

[BobA]

Ok so you have a pro amp with its own PS.    The hum is probably from a ground loop or impedance mismatch on the input to the amp.   What are you using to feed the amps inputs? What outputs are you using on your PC and what cable arrangement is being used?   Your amp is looking for a high impedance input so your PC output should be the line out.

Added link re groundloop:
http://www.epanorama.net/documents/groundloop/

[deoblo85]

here's pics much simpler to explain

[BobA]

Is your PC and the amp plugged into the same 120V circuit?

Is the output of your PC audio a line level (non amplified, high impedance) or a amplified output?

What are the 2 identical cables that go into what looks to be your AC power distribution for your juke?

[deoblo85]

first - yes

second - i have no idea its just a speaker jack for the pc , how could you tell?

third - neutrik speakon speaker cables they go to my speakers,they come out of the amp with banana plugs into the neutrik speakon plugs

[BobA]

You would have to check your MBoard manual to see what type of output the speaker jack provides. 

[richms]

Grounded amp, grounded power supply and a mo-bo not in a case will cause a ground loop.

Also, make sure that all the other mixer inputs are down.

But then you need to get a ground on the motherboard, since you are not putting it on a backplane you would need to run a cable from the case of the PSU to a mounting screw of the motherboard, best to one near the audio plugs.

Whats happening is that the powersupply will have some noise between the black leads on the motherboard side and ground on the AC side which is coming thru the amp.

Otherwise see if there are balanced inputs on the amp since that should get around the problem but I don't know if that amp has them or not, and just putting RCAs into balanced doesn't always work too well anyway.

[deoblo85]

Thank's i'll try grounding the motherboard and see what happens 

[deoblo85]

That was it i grounded the motherboard and grounded the amp to the motherboard and the sound went away Thanks........ richms  and thanks boba for helping.

[kizer]

Ok, I must ask. How did you ground the amp and the mother board together? My luck I would blow up my PC.

[richms]

When I did mine, I just put a ring terminal under one of the mounting screws near to the audio jacks, and bent it up so that the connection came off perpendicular to the board so it didn't hit anything.

I wouldnt risk a spade terminal sinceit may work loose and hit something.

[deoblo85]

just ran a ground wire from the power supply ground to one of the motherboard screws and the amp ground to a mother board screw next to the other one (it worked perfect)