Axiom Home Page Forums General Discussion Technical Questions Humming from EP350

Hey everyone. So i have had my Vassallo Series system for about a year and a half now. I recently moved into a new apartment, and first thing i did was get my system up and running. I finally got around to getting the sub added on as i wasnt sure how the neighbors would react. When i plugged the subwoofer in, there was a really annoying hum from the subwoofer. I believe that this is the infamous ground loop issue. I had purchased a subwoofer cable, and the ground loop isolator/filter from axiom as i had the same issue in the old house. However, it is not working for me here, and the hum continues. Just to give some specifics:

Onkyo TX-SR604
Vassallo wood series m3's, 2 qs8's, and the ep350 v2

Axiom subwoofer cable

Axiom Ground loop isolator plugged in the following fashion: cable line to splitter. splitter to internet modem, and splitter to isolator then to cable box.

fios tv service with motorola set-top-box

phillips 37" 720p LCD

All speakers are setup with o2 free speaker wire, using the axiom banana plugs

the subwoofer is plugged directly into the wall on a completely seperate circuit than the rest of the equipment.

any suggestions on what i should do? thanks in advance for all of the help!!

Kokil, welcome. I'd suggest disconnecting the sub cable to see if the EP350 hums when plugged in and turned on without any audio connection to the rest of the system. If it does, then it isn't a ground loop and maybe the sub amp was damaged during the move. If there's no hum when the sub cable isn't connected, then a ground loop appears to be the problem. The cable line wouldn't appear to be the source because of the isolator being used, but to double-check, disconnect the cable TV line temporarily. Assuming that the TV cable isn't guilty, a loop may run between the different circuits for the sub and the other audio equipment. Try to at least temporarily plug everything at the same outlet. To be continued presumably.

I ran into the same problem.Never had any humming until we had our cable provider install a digital phone modem.They installed another splitter on our cable line and didnt ground it.I ran a ground wire from the original splitter to the new one and the hum went away.

Darcy

Gents, thanks for the suggestions. I asked my boss for a work from home day specifically for this, so i will be testing the theories, and hopefully resolving the issue. I see that the cable splitter isnt grounded, so i will do my best to ground that. also, i am going to take everything else out of the equation and just have sub and receiver plugged into one power strip to test this correctly. I will have an answer for you all shortly.

So i took the suggestions given. Before destroying my setup, i plugged the sub into the same power strip as the rest of the equipment. What do you know, the hum is gone. Now my only issue is that i wanted the sub to be sitting on this side of the room, but i will have to modify my setup to make it work. Thanks for the suggestions gents, glad to see that your expertise was able to help resolve this so quickly.

There are electricians on this forum, and they can help more than I can, but if it were me, I would put it back where you had it with a cheater plug.

The problem isn't your setup, it's a problem in the new apartment with not having a common ground.

So there's a ground differential between the two different outlets (probably due to them being on different circuits). You've got (at least) three different ground planes going on. The mains ground of the receiver, the cable ground and the mains ground on the sub. The shields of the signal cables are trying to force them all onto the same ground plane, and creating the hum.

If you want to keep your sub in the old position, using a sub cable that breaks the shield is a good option. That is... the centre pin (positive/signal wire) is connected at both ends, but the shield (negative/drain wire) is connected only at the receiver. If you're good at all with a soldering iron, you can make one. That allows the sub to happily work on it's own ground plane. This is pretty normal in professional audio where you'll have wildly different ground planes across a huge arena or stadium.

I would not suggest a cheater plug. That removes the safety ground, and leaves the shield as the only source to ground in the case of electrical shock. It could (it's a long shot, though) kill you.

Bren R.

See? I knew others would be more helpful than me.

It's a curse I'm used to living with....

The cheater plug is a good idea to test for ground differential, but as a permanent fixture - not so good.

Because I dislike being shocked or electrocuted.

Bren R.

I didn't stop to think that the cable could be modified.

If it was a house and not an apartment, I would have recommended a professional, permanent fix!

I wasn't bird-dogging you on it, Mark, just trying to be funny.

Bren R.

Oh, I didn't take it wrong...just feeling a little guilty in that I made a recommendation that might have fried a fellow Axiom Forum member. Now, if this was AVS......

I ran into the same problem recently. Turned on the EP350V3, and voila, humming. Quickly narrowed it down to my cable provider. Unplugged the incoming cable and no hum. Called my cable provider and explained the problem. The lady on the other end (call service in Atlantic Canada) didn't have a clue. An electrician friend of mine recommended a new power bar with the cable in/out feature. Works like a charm however the cable company is still at fault! Was tempted to try a video isolation transformer from Axiom.

A cheaper alternative (albeit uglier) is just using a 75 ohm-300 ohm transformer connected to a 300 ohm-75 ohm transformer.



These two hooked up to each other. Spades screwed into the screw lugs, plug coax into each f-type connector.

Bren R.

Wrap that combination in some duct tape and yer all set.

I would say electrical tape, but yes. I once had to do something similar when I ran out of hum buckers... only it had to switch the f-connectors to BNC at each end as well. Was much better than the 60 Hz crawl through the source and only had to last the one night.

Bren R.

I HATE when that happens.

I ALWAYS keep a few extra hum buckers on hand. You never really appreciate them until your hum needs to be bucked.



OK- - I'll stop

I have a pair of humbuckers in my Gibson but I would never try to use them to solve this situation.

Don't buck too hard during the humming or you might get tooth marks.

How much hum could a humbucker buck if a humbucker could buck hum?

Okay Kokil, continued(if you're still reading this). So the problem was in fact that the sub amplifier was grounded at two different points and their electrical potential was different enough to cause a hum current to flow between them. If you want to keep the sub in your preferred spot(without running an extension cord)there're at least two solutions: break the ground which runs through the sub power cord by using a "cheater plug"; or break the ground which runs through the shield of the sub cable to the other equipment. If you use the cheater plug the sub isn't grounded through its power cord but is still grounded, as Bren mentioned, through the shield on the sub cable. This is considered to be a less reliable ground and there's a fairly remote danger involved, but the call is yours.

If you want to keep the ground through the sub power cord and cut the one through the sub connecting cable, besides performing surgery on the cable, you might pick up a ground loop isolator such as this one at RadioShack to connect between the end of the sub cable and the input on the sub. You'd also need an RCA plug-to-plug coupler such as this one to connect the cable plug to the isolator plug.

Hi BrenR and all,

This suggestion is fine if you're on conventional cable. But this will not pass High Definition digital cable signals (5 MHz to 1.5 GHz) without degradation. The Axiom cable ground-isolation transformer will pass all HD signals with no degradation, which is why we introduced it.

http://www.axiomaudio.com/groundisolator.html

I did abunch of tests with various models until we found one that passed all the HD signals untainted. Note, this transformer and other isolation types cannot be used with satellite dish receivers.

Regards,
Alan

True. I keep forgetting that some people get that new-fangled HD stuff.

Bren R.