Speakers crackling, popping & banging

[kiloran]

This is the second minor issue with my new 940. Completely stock audio system (radio-cassette, '93 SE)

It would appear that the speakers are live even when the head unit is switched off and the key is out of the ignition. The car starts making random noises, like it's haunted (well, that's what I've told my 10yo ) - the sort of noise you get when you plug headphones in - pops, crackles, bangs. Only happens when they're not being fed from the head unit. First time it happened I thought the car was falling apart it was so loud. Workaround is to tune the head unit to an empty frequency and leave the volume on the lowest setting, they don't do it then. When I insert the key and move it to the position prior to start there's a noticeable hum, a bit like you'd get without the correct aerial suppressor.

What's the likely issue? Dodgy ground? Bare speaker wires shorting somewhere? Is it normal for the speakers to be live if the key's out of the ignition? I'm only concerned about battery drain if the car stands for a while, it's kind of appropriate a 27yo car should be haunted!

[Laird Scooby]

First question is does it have the separate amplifier or is it the integrally amplified head unit?

Before you answer that incorrectly with "It's the standard system so no amplifiers", on many cars Volvo fitted a separate amplifier.

This is a squarish black box with big fins on it, under the dashboard above the accelerator pedal.

It sounds (no pun intended) as if there is some sort of problem with the amplifier unit and it's causing noises as the capacitors inside discharge on power off.

That's my best guess at the moment but ned more nformation to make a better suggestion.

Meanwhile eject that Ghostbusters Soundtrack tape from the deck and call in the exorcist!

[kiloran]

I'll have a look next time I've got the kick panel off to check the HCV, thanks.
Good point re the caps, that would make sense as they'd retain charge after the key is out. Sound system is otherwise very good, very impressed with it given the size and age of the speakers. Nice warm sound and probably going to dust off my cassette library!

[kiloran]

Originally Posted by kiloran

This is the second minor issue with my new 940. Completely stock audio system (radio-cassette, '93 SE)

It would appear that the speakers are live even when the head unit is switched off and the key is out of the ignition. The car starts making random noises, like it's haunted (well, that's what I've told my 10yo ) - the sort of noise you get when you plug headphones in - pops, crackles, bangs. Only happens when they're not being fed from the head unit. First time it happened I thought the car was falling apart it was so loud. Workaround is to tune the head unit to an empty frequency and leave the volume on the lowest setting, they don't do it then. When I insert the key and move it to the position prior to start there's a noticeable hum, a bit like you'd get without the correct aerial suppressor.

What's the likely issue? Dodgy ground? Bare speaker wires shorting somewhere? Is it normal for the speakers to be live if the key's out of the ignition? I'm only concerned about battery drain if the car stands for a while, it's kind of appropriate a 27yo car should be haunted!

For anyone with the same problem it turned out that the amp is permanently on. Haven't diagnosed exactly why because there's a simple workaround - just pull fuse 26 until you need tunes (from the driver's seat that's furthest fuse to the right on the bottom row in the fusebox). With the amp fuse out the dash panel speakers still work in all their tinny glory (but, conveniently, loud enough for sat nav)

[bob12]

Depends on head unit model number which on the front. At '93 with cassette I would assume it still has an amp.

Bob