Axiom Home Page Forums General Discussion Technical Questions Humming coming from subwoofer

Can anyone help me out here? I have a sub that's about 5 years old. I bought it used, but optically and technically it's in good shape. However, no matter where I plug it in, it hums. It's not that loud, but noticeable. It even hums when I unplug the input from the receiver. It has a standby mode when plugged in but not turned on, and it even hums then. I've ruled out a ground loop problem, by bypassing the ground part of the plug.

I've also tried plugging it in in various outlets, but with no change. Is it possible that the transformer inside the amp is simply this loud?

The brand is Elac. A german company. This little 8" sub cost about $550 new, and Elac is a respected company here, so I don't think it's just a piece of crap. I wonder what the deal is.

I would appreciate any input.

Thanks!

As it is humming with nothing connected I would say it is a problem with the amp and it is picking up noise coming off it`s own tranformer or power supply.

Are you still living in Germany, or are you back in the states now? Maybe it is a voltage issue, but I'm guessing it would not work at all then.

I see Elac took the Rubiks cube sub to market......

http://www.geekalerts.com/rubiks-cube-subwoofer-from-elac/

Yes, well with the receiver connected, it hums too. It's just not noticeable until there's a pause in the music....

The noise doesn't come from the transformer itself, but rather from the speaker.

Usually if it only hums with the receiver connected to it then it could be traced to a ground loop back to the receiver but it still makes noise with nothing connected which is why I say it is the amp which really is the only other possible choice.

What Jay is saying is that since it hums when nothing is connected except the power cable (you've ruled everything out), then it is the amp. The noise you hear from the subwoofer driver is from the internal amp.

Barkeep, as Jay and Randy have pointed out, if it hums even when no other connection other than the power cord exists, it can't be a ground loop hum because there's no connection to form a loop. That points clearly to the internal sub amp itself and since it isn't a mechanical hum from vibrations in the transformer, but an electronic hum coming from the driver, there appears to be a fault in the power supply section. The rectifier and filter capacitors do the job of converting AC from the wall outlet into clean DC to be used by the amplification section. It's likely that the rectifier or a capacitor is going bad and needs to be replaced if the hum is too annoying.

Hmm, that's a new and interesting perspective. Thanks. Now if I only knew which component(s) to change out. There are two big caps at 6800 uF, and some other components. Here's a pic. Is there any way to test the components to see which one(s) need to be replaced?

Are you familiar with working with circuit boards?

Actually, I studied electrical engineering, but specialized in automation. So I do have a bit of experience with circuits, but not really any with amplifier circuits.

Can anyone point out to me what the rectifier and filter capacitors are? I'm curious to try and fix it myself before I have to sell it as somewhat defect.

Well, you already correctly identified the two 6800 uF capacitors(which are the most likely suspects)in a previous post. The rectifier is a grouping of usually four diodes(which aren't clear). But no, there isn't any simple way of determining without diagnostic equipment which are failing.

Thanks for your answer JohnK. So you think that the 6800uF caps are responsible for the annoying humming. Are they part of the rectifier circuit? Or do they have a different function?

Thanks!

they are capacitors which store power. I think my Odyssey amps had a total of 120000 uF capacitance so when you need power it is there..

The rectifier and capacitors perform different functions in the power supply section of the amplifier, but the net result is to provide clean, smooth DC instead of the incoming AC. The rectifier changes the AC which fluctuates between about +/- 170 volts(in N. America)to either a plus or minus DC output which fluctuates from max to zero. The capacitors take this fluctuating DC and store the pulses, then release them in a smooth DC to the amplification section. The result should be inaudible hum and noise when they're operating properly.

Is it common that the smoothing capacitors go kaput on amps that aren't that old yet? I could imagine that happening on a 20 yr old amp, but this one is still relatively new and at least optically in great shape. I wonder if there's another way for the caps to go downhill other than just aging?

Think of it like buying a Ford, new or old they're still $#@## lol
Sorry, if I offended anyone , " Who's driven or bought a Ford lately."

Well, you DO have a way about you, don't you?

No, I've never owned a Ford.... and not for any particular reason.

At least Ford is still owned by Ford and not the government

I've owned 2 Fords. One was the best car I've ever had. The other was the worst car I've ever had.