Popping JBL subwoofer when system is off


New member
Username: Larston

Post Number: 1
Registered: May-05
I've had this JBL sub for a little over two years. It has always worked flawlessly with great sound. About 6 months ago, it started popping when the system is off. It's quite a shock when the house jumps at 3:00 in the morning! Sometimes I'll hear it start to buzz or sound like static about 5 minutes before the pop happens. I'll hear a steady, very quiet noise for a few minutes, then it'll go quiet for a couple minutes, then BOOM! It may do this every other day for a couple days, then I may not hear it again for a couple weeks.

The box is connected to the sub out port on my Sony E-series amp with shielded coax. As I said, I didn't hear this for about a year and a half after it was initially hooked it up, so installation doesn't seem to be the issue. Any ideas what the problem could be?

Bronze Member
Username: Thx_3417

Bournemouth, Dorset United Kingdom

Post Number: 63
Registered: May-05
Well it can't be square waving not if its not in use, this is strange could be the amplifier something funny with maybe a dry joint on the PCB printed circuit board.

Or an electronic gremlin, in the electrical wiring or it could be,

A poltergeist, no I'm not kidding around you mentioned the time 3 am in the morning now something is not right hear, though I'm sure you will find the funny, buy the way I'm running the JBL 4645 THX approved cinema sub bass for 7 years and it's a force to be reckoned with.

Jedi Blasters Lightsabers, JBL


Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 3818
Registered: May-04

Two possibilities:

First, a problem which is causing the auto on circuit to activate. Unless this sub is unlike other powered subs on the market, it uses a sensing device to detect when to come on and when to go into standby. You need to determine whether the sub is receiving a signal that is causing it to turn on and off independently. Unplugging the input cable from the receiver at the sub end will determine whether there is a signal from the receiver. This will cause a loud buzz as the ground is made and broken first on an RCA plug. So unplug the sub from the wall before you plug and unplug the sub. My guess would be this is not the cause of the problem. If that's the case, proceed to the next possibility. If this proves to be the cause, you will need to determine whether the sub or the receiver is at fault. You can probably accomplish this by switching to the high level inputs on your sub.

Second, the power supply capacitors are the storage devices in the system. They will carry and hold large amounts of voltage for long periods while the sub is in standby mode or even unplugged from the wall outlet. If the sub still makes this noise when the cable from the receiver is unplugged, you have a bad capacitor or a portion of the system (probably in the standby mode switching) which is causing a capacitor to discharge on its own. Since these capacitors carrying potentially lethal levels of voltage, if this appears to be the case, the sub needs to go into the repair shop. DO NOT ATTEMPT ANY REPAIRS YOURSELF. If you are not familiar with the inside of a power amplifier, you can end up dead. And just in case you ignore my advice about this, when you stick your hand inside the sub's power supply, have someone standing by with a 2X4 to knock you off the supply capacitor when it grabs hold of you.

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