Buzzing from speakers with engine running!

[austinsom]

I finally got around to fitting my AMP. It was all wired and fitted in the boot, and as with the last two I had, couldn't get it to light up with the remote on.

Now I knew the amp to be good, as it was factory fresh, so I took the head unit out and checked the remote on wire, no +12v on it. So I removed the wire from there and hooked it upto the switched live for the headunit.

With the accessory position switched on all seemed to be working, the amp was getting power, and there was a crisp clean sound from the speakers. At this point I pushed the head unit back in.

BUT

With the engine running there is a constant hum from the speakers, and as you blip the throttle you get a wurring noise that rises and falls with the engine speed.

Is this likely to be caused by having it hooked to the switched live, or do I need some sort of filter for the amp??

Any help, as always, much appreciated

Cheers,

Greg

I have also CC'd this in ICE as would like to get to the bottom of it quickly!!

[Geeman]

The gain from the AMP is turned up too much. Use the volume on the head unit so that it max's out right at the top, rather than lower down...

I had the same problem. Took it in to get looked at, with the view to getting a supressor put in, but they twiddled with the gains on the AMP and now it's perfect...

HTH

Giles.

[austinsom]

Hi Giles,

Thanks for the reply, but the buzzing is the same whether the gain is all the way up, or all the way down.

It seems to happen when anything electrical in the car is used. I think it could be to do with the switched live. Anyone have any other ideas?

Cheers,

Greg

[Ant]

Check the engine earth strap dude, passenger side going from the sump corner to a stud on the chassis leg

prone to looking OK but being scrap

[austinsom]

Thanks for the tip Ant. As I know nothing about electrics, would that make a difference between having the engine off, and having no buzzing, and having the engine on and having buzzing?

Would it be worth buying a new earth strap anyway?

Cheers,

Greg

[320Touring]

having a good earth is the key to getting good tunes in your car!

amp should be earthed to bare metal pref with a bolt or screw, also check the earth strap as ant suggests.

Make sure all the connections are clean and tidy (no stray strands of wire)

I'd also get the fact that the remote off line doesn t have power checked out-not too keen on running it from the switched live from the stereo...

good luck

[austinsom]

I'll have a look to see how tidy it all is, but I checked with a torch earlier, and nothing is touching the case of the amp.

I have earthed it using the bolt that holds the jack against the car in the boot as that uses a nice big screw, but I may relocate it if I'm told it's not a good idea!!

Would my choice of amp be causing a problem?

I'm just puzzled as to why it happens only with the engine running...

Cheers,

Greg

[alpinachris2]

looking forward to hearing how you solve this problem ,as i have the same thing going on with my car at the minute.

[Jos]

The reason it only happens with the engine running is because when the engine is off the alternator isn't doing anything. It's the bit that is making the noise.

Some cars have a capacitor on the alternator that suppresses this. I dunno if the e30 engines had or not. They basically go across between +12V and ground at the alternator connection. If that's not enough, you could try a large choke (inductor) inline with your amp, or a capacitor across the amp power terminals.

The best way to avoid interference like this is to run your negative back to the battery terminal too, then it isn't using the car body as the return path.

[austinsom]

Solved the problem... Removed the amp, and wired the speakers to the head unit!!

Cheers for all the advice guys!

Greg