Thanks in advance for reading:

I have a new ep350 sub, and seem to have an ever present, rather soft, hum. The hum is present when my receiver is off, with the cable removed from the receiver, and even after the sub has gone in to "sleep" mode. With the sub in sleep mode, I can feel a slight vibration on the heat sink of the sub.

Any ideas where to start with this?

Thanks for your help!

Is the sub plugged into the same AC outlet as the other equipment, or a different one in the room? I had a similar problem when I had my twin 350's plugged into a different outlet for whatever reason.

The sub is plugged in to a different outlet - my sub is behind my screen and my receiver is in a different room.

Do you have cable television service?

I had a hum with my ep 500 that completely went away with the Axiom Ground Isolator

FIOS for TV and Internet but neither is currently present in the theater or connected to the circuits that the receiver or the sub are connected to... =(

Different outlet will do it. You can try a cheater plug (but not for permanent install, according to the electrician hawks around here) to see if that gets rid of the hum.

But why would it hum when the sub is not connected to the receiver and in sleep mode?

It is still plugged into an outlet. Just as a test, do you have a long extension cord you could run over to the same circuit, just to see if you get different results?

This may not be the problem, but the IT person in me likes process of elimination.

I agree, next test will be to run an extension cord. Thanks for the idea!

Josh, since the hum occurs when the sub has no connection to the receiver or anything else in your setup, this isn't a ground loop because there's nothing to form a loop. A hum simply because the sub is plugged in indicates a possibly defective sub amp power supply section. Contact Axiom technical assistance directly for further information and possibly a substitute unit.

About 2 months after owning it, I had a hum, and another issue with my SVS sub where it would "pick" a deep note and play it at VERY high volumes during the day, when it wasn't in use. I tried all sorts of things. I had these two sound issues when it was in sleep mode or not. I would unplug the inputs and have it just plugged into power, and still had the hum. The loud, non-stop, deep note rumble thing would happen randomly, and usually with several days in between incidents. I changed outlets, I used outlets on different circuits, , I used a different power cord, and tried leaving the sub unplugged for a day and then plugged it back in.

The problems continued.

I called SVS and they sent me a new amp (which is how I ended up with an extra SVS amp). Well guess what. It did the exact same thing. I was at my wits end, and then I tried something simple. I plugged the sub into a good surge protector, and all of the problems went away. I then went out and bought a small (but highly rated both technically and in reviews) single plug surge protector that mounted right on the outlet, and again, no problems.

What was to account for the loud deep output was that we were getting a series of power spikes during the day to our part of our neighborhood. Why? Well, my one neighbor whose house goes into the same power "box" that our house does was doing some welding with a welder that he borrowed and started doing it the same time that the problem started. He was using it for some small welding projects that he was working on, so that is why it would only happen every so often. Anyway, he would draw enough juice that when he started to weld, he would turn it on and do a couple of "zaps" which would draw current, and then shut off the welder that the timing seemed to cause a surge at our house. I ended up testing this by running an extension cord from inside our house to his garage and put a surge protector on the end. As soon as he would start to weld, zap-zap-zap, and the surge protector light with go on that there was a surge. Somehow this surge would turn on the sub and "confuse it" to create a deep, but very loud sound. Needless to say, I called the power company and they made some changes (wouldn't say what) and it wasn't an issue. The surge protector also seemed to get rid of the hum, and by the time I even thought about that again, he was done with the welder, and the power company made their changes.

Long story short, try something simple (besides calling Axiom) and just put the sub on a surge protector just to see if it does anything.

Oh, and I am using the original sub amp without issues for several years now (and the "new" amp that SVS sent me is sitting in a box waiting for me to put it to good use).

Update:

Tried just about everything suggested - cheater plug, extension cord, etc.

With nothing plugged in to the input, with all other electronics turned off, using cheater plug, etc - I still have the hum. Will give Axiom a call.

Thanks for the help,

Josh

Welcome Joshmkiv,

I seems there might be a problem with the amp and not a ground loop issue. Let Axiom know of your issue, don't worry, Axioms customer support is top notch and will take good care of you.

Good Luck!