hum when rear speaker rca is connected

[cmotavalli]

I have been trying to find out why I hear a hum from all my speakers when pressing on my brakes. If I disconnect the rear speakers RCA from my amp the hum goes away. I have now plugged in a ground loop isolator which is masking the problem but I am wondering what is causing it. I tried swapping the front and rear speaker rca from the amp and the sound comes back. Could it be the amps grounding, the rear speakers RCA, or a connection within the rear speakers themselves? Getting behind the radio to run new rca cables to test is not easy and if it could be the amps ground would rather try that first.

Thanks

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[jrdnhsnbrg 10+ year member]

Try moving the RCAs to the other side of the car maybe? Run them down the middle?

 

[keep_hope_alive Premium Member]

a broken RCA (internal) can cause this. or it can be internal to the amp. verify if the hum is in all speakers or just the speakers assigned to the "rear" RCA?

 

[jrdnhsnbrg 10+ year member]

a broken RCA (internal) can cause this. or it can be internal to the amp. verify if the hum is in all speakers or just the speakers assigned to the "rear" RCA?

He said it only happens when he hits the brakes, is the amount of current carried by the wires to the taillights enough to cause interference in the RCAs? If the RCAs are ran directly next to the taillight wiring it might be able to cause interference.

 

[cmotavalli]

The noise is only when I hit the breaks and is in all speakers not just the rear ones. I will try to rerun the rca's but the rca running the front speakers isnt causing a hum even though it is run with the rear rca all the way to the trunk.

 

[jrdnhsnbrg 10+ year member]

Try new RCA's when you run them, too.

 

[keep_hope_alive Premium Member]

the brakes (and other things) can add noise on the ground system, and that noise can be amplified when you have ungrounded signals (since the amp and vehicle share the same ground plane.

if it is in all speakers but only when you use the "rear" RCA's, but not when you use the "front" RCA's then that points to an RCA with a broken internal lead, likely a broken connection to the shield.

i use a 2-piece head shell RCA's so i can look at and repair connections. the cheaper molded RCA head shells are not repairable.