[Huck]

I have a hum coming from my music only  powered subwoofer,with nothing plugged in,only powered up.Here is what I have tried so far with no success:
-plug into a different circuit
-use a 'cheater" cord,3 to 2 prong
-changed out xlr cables
-removed the ground(shield)from pin#1 on the speaker end
-tried a Ebtech Hum-X hum eliminator
I have tried a plug-in circuit tester and all good.
This is a 'pro' type music only subwoofer with xlr's,whereby the signal goes through the sub x-over at 80hz and from there to my powered Yamaha tops.
Not sure now if it's my sub or my house wiring??!!
 Gound loop,I guess?! What next to try?? Thanks,Huck

[SteveFord]

Bad ground inside the sub?

[Odal3]

I had a hum on an external power supply and I got the advice from the forum to check all screws, cables, touching surfaces connected to the transformers, etc. to make sure it was not vibrating. This took care of most of my issue. Try hold a hand with little pressure to the plate amp to see if that changes the sound. It may not be the problem with your sub but worth a try.

[ctviggen]

If there is nothing plugged into the sub, the sub is turned on, and the sub hums, then something is wrong internal to the sub.

[Meguerra]

Try using a cheater plug on the power cord. it eliminates

 the ground pin. This worked for me.

[Huck]

Try using a cheater plug on the power cord. it eliminates

 the ground pin. This worked for me.

I basically tried the same thing,by cutting the ground pin off one side of my 3 prong power cord and no change....these "cheater plugs"are illegal here in Canada,so very hard to find! I changed out all my 4 xlr cables to a different brand and the hum is still there,but has dropped from 48.5 db to 43.5db which is more tolerable. Thanks,Huck

[Phil A]

Using a cheater plug can be dangerous - http://en.wikipedia.org/wiki/Cheater_plug

[Phil A]

Several months ago I replaced a 3-channel amp (for the center and surrounds) that would trip the circuit breaker about half the time (only thing on that circuit but the arc fault breaker was a bit finicky) with a mono block Class D amp for the center channel.  Had a hum.  Rather than rip all the stuff apart I had one of these laying around - http://www.amazon.com/dp/B0002E4YI8/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=321FECHQA1Z6W&coliid=I2I3VNO4OQRS43

Van Alstine also makes -
http://www.avahifi.com/index.php?option=com_content&view=article&id=270&Itemid=239


I had formerly used the Ebtech device in an old house when I had a hum with a subwoofer hooked up and I found using it on the projector (for whatever reason) eliminated the hum.

[Phil A]

Here's another write-up on the dangers of cheater plugs - http://www.ehow.com/info_11373614_three-prong-plug-converter-safety.html

[Huck]

I just took apart my new xlr cables which had lessened the hum from my subwoofer starting at 48.5db with the "old' cables and now with the "new" cables at 43.5db, which I can tolerate for now. Seems that the"new" xlr's have the pin#1(shield)  soldered to the chassis by way of a tiny jumper wire going from the pin#1 to the chassis connector. For sure the soldering job on these xlr's are not the best,but for now,they work! Huck

[Wayner]

Using a cheater plug can be dangerous - http://en.wikipedia.org/wiki/Cheater_plug

If you are going to play your sub on a wet concrete floor.........Remember, your body has to become part of the circuit, and your environment has to be rich in conductivity. How the "nutty professor" got zapped in the Wiki article is a puzzler. All high fidelity equipment does not need a 3-prong plug, (unless it's used against the usual recommended installation environments.....which is indoors on dry floors).

I have 8 amplifiers and none of them have a grounded plug.

Wayner   

[Speedskater]

Some other forums don't permit posts suggesting dangerous practices like cheater plugs.

[Wayner]

I never suggested once on using a "cheater" plug. I said that grounded equipment in a home environment, under normal operating conditions, is simply not necessary.

My 8 amplifiers have no ground, and that is the way they came from the manufacturer. A couple of the amps are relatively new.

Industrial or commercial equipment is a different story. They actually might end up in service outside in the rain or at least in the elements, unlike a typical home (unless your home has a leaky roof.......).

[Wayner]

Back to the hum topic, some hum is not electrical in nature, but rather mechanical. If the transformer in your amp's power plate is loose, things can vibrate and be sympathetic to the 60hz magnetic field. Even steel screws that are loose can vibrate.

Have you checked the polarity of your home's outlet? That could also have the hot and neutral switched.....

Wayner

[Huck]

Back to the hum topic, some hum is not electrical in nature, but rather mechanical. If the transformer in your amp's power plate is loose, things can vibrate and be sympathetic to the 60hz magnetic field. Even steel screws that are loose can vibrate.

Have you checked the polarity of your home's outlet? That could also have the hot and neutral switched.....

Wayner

Thanks...I used one tester similar to this :http://www.homedepot.com/p/Gardner-Bender-120-VAC-Outlet-Tester-1-clam-5-clams-master-GRT-3500/202867894   ...and it checked out o.k..Huck50

[Phil A]

I have a tester similar to that and that will tell you if the receptacle is wired properly.

[Huck]

I am using newer xlr cables that have a jumper wire from the pin#1(shield) to the chassis ground via connector barrel and the hum has dropped about 5 db,which I can live with....the hum is still there,but not near as bad when using these new xlr mic cables.
 One day I will take the sub in to the repair depot and get it checked out,or I will just send in the whole amp module,which would be easier than lugging around a 60lb sub.Thanks,Huck

[Wayner]

Did you ever think that you just have a shitty sub-woofer? The power supply board could be a bad design for example and you could beat your head against the wall for ever trying to find gremlins and it could be just the sub.

Don't mean to insult your equipment, but it is something that could be on the list, no?

XLR connector not wired correctly or XLR connector on sub not wired correctly?

Like pins 2 and 3 switched? Not sure on that one. What kind of preamp are you using that has XLR outs for LFE?

Also, is the sub's power cord plugged into the same spot as the preamp or main amp?

Wayner

[Huck]

RCF subs are not cheap,but it's possible something is going on inside,as the hum was there from day 1 (2010) My dealer tried swapping out a control board,but no luck....he just loosened the board and the hum basically stopped....that was until I changed out my RCF tops 2 months ago for some Yamaha's,maybe cheaper electronics inside these....I dunno,but I will most likely ship the RCF amp module to the authorized repair spot 2 hours away,for a check-up. Huck

[Speedskater]

I am using newer xlr cables that have a jumper wire from the pin#1(shield) to the chassis ground via connector barrel and the hum has dropped about 5 db,which I can live with.....Thanks,Huck

Inside a chassis the pin#1(shield) should only be connected to the chassis (with a very short jumper) but not connected to the circuit common(Ground). Yes the circuit common(Ground) is also connected to the chassis but that's a different story. In pro audio the XLR shell/barrel is not connected to the shield, but the reason is that with all the long extension interconnect cables the shell could contact metal at a different potential.
Once again the XLR pin#1 is a shield it's not part of the audio circuit ground.