What the H*ll is this noise?

[Jack Hammer]

I am helping my friend move and when we plugged her subwoofer in, it makes a noise that sounds like very loud grumbly buzzing hum. The sound is 100% from the sub. As soon as we plug it into any outlet (tried several) with or without an interconnect and regardless of the volume or Xover setting, it makes a noise similar to touching the end of the interconnect with your finger and shorting the rca jack, but much, much louder.

Is her sub shot? or is there something we can do?

Thanks

Jack

Oh yeah, its an Infinity BU-80. She says it made the sound at some point before the move but she doesn't remember if she just left it off or if something was done to it.

 

[Wid]

Sounds like a ground loop.

 

[Jack Hammer]

Sounds like a ground loop.

That was my initial reaction. Except this is more of a really loud barking(?) noise as opposed to steady hum. We tried different outlets on different circuits and the sub makes the noise as soon as you plug it in, regardless of the volume setting or Xover setting. I'm thinking maybe the amp is fried, or something?

Jack

 

[Seth=L]

Does the sub work with a source fed to it? What it sounds like to me is that you are getting pure AC noise. If the sub does not pick up a signal from a source I would say it has serious problem. Could be a leaking cap. How long did you have the sub plugged in while it was doing this?

 

[markw]

My gut feeling is that something in the sub amp and is slowly dying and shows it's displeasure only at times. Unless you know someone who can troublshoot these amps down to the component level, I'd say get it serviced if it's worth it.

Beyond that, I'm outta bullets.

 

[Jack Hammer]

Does the sub work with a source fed to it? What it sounds like to me is that you are getting pure AC noise. If the sub does not pick up a signal from a source I would say it has serious problem. Could be a leaking cap. How long did you have the sub plugged in while it was doing this?

As soon as I plugged it in it started to make that noise. It was loud enough to startle me and cause the sub to visibly shake. I didn't even have the sub plugged all the way into the outlet before I pulled the power cord out. I got the same results regardless of where I plugged it in (this was all with the interconnect not attached).

She said she thinks the sub made that sound a few years back but doesn't recall what came of it. She's not even sure if the sub was even being used at her old place. It may have been sitting there unplugged for the last few years. Now I'm trying to be psychic about it.

Jack

 

[mtrycrafts]

As soon as I plugged it in it started to make that noise. It was loud enough to startle me and cause the sub to visibly shake. I didn't even have the sub plugged all the way into the outlet before I pulled the power cord out. I got the same results regardless of where I plugged it in (this was all with the interconnect not attached).

She said she thinks the sub made that sound a few years back but doesn't recall what came of it. She's not even sure if the sub was even being used at her old place. It may have been sitting there unplugged for the last few years. Now I'm trying to be psychic about it.

Jack

Sounds more than a ground loop issue at that volume level. Try to plug it in with nothing else connected, insert 2 RCA cables, probably before you plug the AC in, and short the ends of both RCA, individually. Use a wire or alligator clip.
It sounds as though it is getting a signal input in the amp from someplace, at a pretty good level. Maybe a cap to ground has failed?

Probably time for another sub a better one?

 

[Seth=L]

When the IC blew in my M&K I replaced the fuses thinking the circuits were fine. When I placed new fuses in the unit it hummed very loud with AC noise, visible cone movement NOT GOOD!!!! Though this may not be the case with said subwoofer, just that anything is possible.

 

[Jack Hammer]

We decided it's blown and not worth taking in for repair. Her mains will be fine set to large for now. The funny thing is it bothers me more than it bothers her. Her attitude is "if it doesn't work, just throw it out, no big loss." I'm like, But it's your SUB!

Jack

 

[Seth=L]

Take it and salvage what you can I guess.

 

[Intradio]

Loud Noise

Sounds like the electrolytic filter capacitor in the sub amp power supply has died. The chemical electrolite does tend to dry out over time especially if the unit is not used, resulting in AC leakage.

I would estimate approx $15 - $20 for a new one but it must be soldered into the board correctly. Any electronics service shop can do it but the labour cost will far exceed the part cost.

Good Luck
Int.