Help with a JBL L8400P - Loud electrical hum

[Kees77]

Hello

I recently purchased a JBL L8400P sub and have mixed feelings. It is very accurate and delivers clean, crisp bass but I wish it was louder compared to my other speakers. I have to max the volume on both the LFE channel and sub just to get it at the same volume as the front loud speakers. Is this normal? My dad's 12" PSB is much louder at half volume and it was a cheaper sub.

Second issue (the real issue) is that I hear a loud electrical hum when it is on and off. When it's on stand/by (red light) it emits a loud electrical sound kind of like overhead power lines if you ever stood near one. It does not stop when the sub turns on either. Is it a defect? Anyone else have this sub and problem? Please help.

 

[AVRat]

Sounds like you have a ground loop issue. Search the site to find other helpful posts.

 

[Kees77]

Thanks for your reply. I did read those posts but think my issue is different. My issue occurs at all receptacles with or without the COAX attached. My other subwoofer (12" Audio Profile) does not have any problem like this in the same location. The noise also got worse over the last 4 days in the JBL. It would have always been an issue if it was a ground fault. The weird thing is I re-attached my old sub (250W) and it sounds way better/louder than my new 600W RMS JBL. I wish I saved the $500.

Do you think the AMP is bad since it emits the noise. The noise is quite loud and over powers regular TV viewing. It is not a deep low it is an electrical current noise.

Can anyone suggest something? I don't want to drive back to Buffalo to fix this. Thanks.

 

[mtrycrafts]

Hello

I recently purchased a JBL L8400P sub and have mixed feelings. It is very accurate and delivers clean, crisp bass but I wish it was louder compared to my other speakers. I have to max the volume on both the LFE channel and sub just to get it at the same volume as the front loud speakers. Is this normal? My dad's 12" PSB is much louder at half volume and it was a cheaper sub.

Second issue (the real issue) is that I hear a loud electrical hum when it is on and off. When it's on stand/by (red light) it emits a loud electrical sound kind of like overhead power lines if you ever stood near one. It does not stop when the sub turns on either. Is it a defect? Anyone else have this sub and problem? Please help.

Disconnect the interconnect to the sub. Does it still hum?
Do you have a cable TV connected to the audio system directly or indirectly through the TV. If so, disconnect it at the wall and if you have a cable box, disconnect at the cable box, both video and audio cables from the box. Still hums?

As to your volume issue, no that is not normal what you are experiencing. Perhaps you need to connect the sub with a Y splitter so both the left and right ch input is activated?

 

[mtrycrafts]

Thanks for your reply. I did read those posts but think my issue is different. My issue occurs at all receptacles with or without the COAX attached. My other subwoofer (12" Audio Profile) does not have any problem like this in the same location. The noise also got worse over the last 4 days in the JBL. It would have always been an issue if it was a ground fault. The weird thing is I re-attached my old sub (250W) and it sounds way better/louder than my new 600W RMS JBL. I wish I saved the $500.

Do you think the AMP is bad since it emits the noise. The noise is quite loud and over powers regular TV viewing. It is not a deep low it is an electrical current noise.

Can anyone suggest something? I don't want to drive back to Buffalo to fix this. Thanks.

If you have the hum even when the coax is disconnected, you have a problem. Is the power cord a 3 prong cord or 2?
If it is under warranty, call JBL for a resolution and an exchange. Be sure to tell them it hums with no interconnects attached.

 

[Kees77]

Hello

The cord is a 2 prong and the ebay store will fix it. It is a 150 mile trip for me to drop it off though. I also plan to tell them it was not loud. It seemed weird that everything was maxed just to get it level to the 6 surround speakers. I had high hopes for this sub.

 

[TLS Guy]

Hello

The cord is a 2 prong and the ebay store will fix it. It is a 150 mile trip for me to drop it off though. I also plan to tell them it was not loud. It seemed weird that everything was maxed just to get it level to the 6 surround speakers. I had high hopes for this sub.

You sub has a loose mains transformer core.

 

[Kees77]

You sub has a loose mains transformer core.

Thanks for your reply. I've also noticed that it chirps when it turns on from stand by. It also goes away when unplugged for 2+ hours but comes back after being on for a few minutes.

Should I attempt to open it up and make sure all the connections are tight? I don't want to void the warranty but would like to avoid 6 hours of driving.

Cheers

 

[TLS Guy]

Thanks for your reply. I've also noticed that it chirps when it turns on from stand by. It also goes away when unplugged for 2+ hours but comes back after being on for a few minutes.

Should I attempt to open it up and make sure all the connections are tight? I don't want to void the warranty but would like to avoid 6 hours of driving.

Cheers

If it does this for 2 hours after it's unplugged, you may have a cap building pressure and leaking. This is rare, but the way standards are dropping in China at the moment, anything is possible. Just return it for another. Stay out of the case.

 

[Kees77]

Thanks for all you input. They are doing the paperwork to get me a new unit rather than fix the current one. I hope it treats me well.

Cheers

 

[mtrycrafts]

Thanks for all you input. They are doing the paperwork to get me a new unit rather than fix the current one. I hope it treats me well.

Cheers

Yes, let us know when the new one is connected if you still have issues or it fixed it.