Temporarily breaking the supply earth while connected to the amp also stops the hum.Īll plugs are three pin and connected to grounded sockets. I'll test with a longer cable along a similar route to the usual signal cable and update later. The iPod was connected with a short cable. If I feed a signal from a battery powered iPod, there is no hum. Initially, I got a worse hum but when I shorted out the loose end, this went away. I have tried disconnecting the signal cable at the amp end. My initial concern was that there was a fault within the sub. I tested by disconnecting the at the sub end. The hum is stopped if the signal cable is disconnected. This earth loop is much larger and picks up a significant hum which I would like to eliminate.įurther evidence that the problem is an earth loop: The mains for this sub is close to the sub and hence not close to amp. I tried a 5m cable with a 2m extension but it was not noticeably better. 7m would be sufficient but that is not a commonly available length. It is not actually that far but the cable needs to go around the wall and not across the floor. The second sub is further away and is connected with a 10m RCA cable. Update, I now know that the amp is not directly earthed but it may be through one of the other devices. There will be an earth loop but it is short and it does not add a significant amount of noise. Its mains connection is into the same power strip as the amplifier. One is close to the amplifier connected with a 1m RCA cable. I have an A/V system with two active sub-woofers.
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