d15 Hum

[logicology]

I just got my d15 today... LOVE IT.

Only problem is I'm experiencing hum/buzz (sounds like 60hz ground loop). I have a professional recording studio in my house plus HT which are both on isolated clean power.

The buzz is loud enough that auddessey can't calculate correctly. All settings on the sub are the ones Brian posted a while back as "default". Its being fed by a Onkyo SR805.

Any suggestions?

[curtis]

Does it hum when nothing is connected to the rca input? Have you tried a different electrical outlet?

If so, and it still hums in those scenarios, might be an amp issue.

[logicology]

I have tried plugging it into a different outlet but that did not help. It does not buzz when I unplug the rca cable.

[curtis]

I have tried plugging it into a different outlet but that did not help. It does not buzz when I unplug the rca cable.

Not buzzing when the RCA cable is not connected certainly points to a ground loop. How long is the cable run?

[logicology]

I appreciate your help, Curtis.

It is a 25ft subwoofer cable from monoprice.

[curtis]

Is it shielded? Do you have another cable you can try?

[pogiboy]

Mine did too the very first time I hooked it up. It also stopped humming when I unplugged the RCA plugs. I also have the same Monoprice sub cable(PID#2683). Tried everything but could not get rid of it. Then I remembered somebody had this same problem and tried an adapter that change the 3 prong to a 2 prong plug (I think it's called a cheater plug). That worked for me. Now it's extremely quiet, except of course when it's rockin my house.

[logicology]

Ohhh... a cheater plug! Thanks for the tip, I'll give that a try tomorrow!

[RythmikAudio]

Ohhh... a cheater plug! Thanks for the tip, I'll give that a try tomorrow!

I don't recommend cheater plug unless it is the last resort. The cause of ground loop is that there are two ground connections in the system, one is interconnect ground that connects everything together while the other one is the ground pin of wall plugs. Some equipment uses 2 prone power plug. For those, literally there is no wall plug ground connection and those will never have ground loop problem. Higher power equipments almost gurantee to have power plug ground connection for safety reason. I have compiled a set of possible reasons for ground loop (feel free to add):

1) poor ground contact on the RCA cable. Even though RCA jack size is supposed to be standard, some are slightly bigger than others. As for plug, there are nonlocking and locking design. The locking design has a locking mechanism and is what I recommend. The nonlocking design may not fit smaller jacks well once it was used on larger jacks.

2) Length of RCA interconnect. If one needs run long cable, I would recommend XLR. XLR is a standard in PA audio. It is more immune to noise. I am not sure if it is effective in ground loop. Maybe someone can share his experience. The problem with long RCA interconnect (I really would recommend 15' as max and 10' is very comfortable) is the ground resistance between equipments now increases, the result is similar to a poor contact of cable ground. Of course, normally a long cable itself is not a problem. It is when it combines with the fact that the sub is now at a different wall plug and there is some small potential drop between at wall plug ground and other equipment's plug ground which eventually leads to ground loop. In this case, a cheater plug is the only solution.

3) house electricity wiring. If the wall plug of the sub and other equipments are on two circuit breakers, we almost guarantee it will hum. This is the worst scenario. In older houses, sometimes the house owner did the renovation and it may not be done by certified electrician. In that case, you can imagine all sorts of additional problems. In these cases, the only solution is cheater plug. I would recommend to use only wall plugs attached to the same circuit breaker if that is possible at all.

If one does settle with cheater plug, please make sure the inteconect ground is well connected all the time because the interconnect ground connection now will be the equipment to ground path and we need to make that path as lower resistive as possible.

[logicology]

Do you risk damage to the amp by using a cheater plug? Will that effect warranty coverage or anything?