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 tech help as would like to get to the bottom of it quickly!!

[placey]

the hum you're hearing is almost certainly to be from your wiring up - only the very rubbishest amplifiers hum when cabled up correctly these days.

rather than taking the remote on from the switched live try taking it straight from the battery +ve terminal via a switch - make sure it's fused with the smallest fuse you can find as it shouldn't draw any real current - and run it all loose to start with. if this works you can mount the switch somewhere convenient - say in a spare switch hole above the head unit.

take a look at the ice article section 9 on cabling - you need to run your power cable well away from the signal cables to avoid interference - drivers side if you're running from bonnet to boot. your earth is also crucial - route this away from your power cable. your remote on lead and music signal cable need to run down the passengers side of the car - this is due to the factory loom placement so none of this is really negotiable. if all this is good and you still have a noise then we need to consider earth loops first then suppression.

i assume in all of this you're running your amp fed by a headunit pre-out? it's not speaker or 'high level' fed is it?

paul

[austinsom]

Hi Paul,

Thanks for the info. The wiring was already in the car when I bought it, and all runs down the transmission tunnel under the carpet.

I hooked all this up and like I said was fine until I started the car. I'm not the most technically minded of people, but am considering looking at the connector block on the radio, as I don't think the remote on, actually connects where it should, so I may try that first.

It is fed by the pre-outs on the back of the head unit, and as I'm only driving a couple of cheap speakers I bought a budget amp. Could that be the problem? It's an splX if that means anything?!

Cheers,

Greg

[placey]

all runs down the transmission tunnel under the carpet.

this could be the problem. try routing your music signal cable away from the power cable.

also can you post more details? e.g. where is the amp? what (gauge) cable is connected to the +ve? what cable to the -ve? and where does that terminate? what head unit is it? which colour wire have you connected the amp remote to? any other details too...

an splx amplifier should be fine if wired in correctly.

if you try routing all the cables well away from each other and the switch idea above and it still doesn't fix your hum one suggestion is that you take out your seats and carpet and bolt in your drivers seat and run it in to your local ice dealer - the installer there should have it sorted in less than an hour - i.e. less than Ԛ£30 as he won't have to de-trim the car to get to the cabling.

alternatively pull it all out and start from scratch - me or others on here can talk you through it wire by wire. it's surprisingly easy and you'll know how it's done for the future.

pity you're not nearer....

paul

[austinsom]

Thanks for the info Paul. Good to know I can get the help required for my slowly increasing skills!!

If I took the +ve off the amp, and attached it to the remote switch on, would that light the amp up? Might be worth trying that first!!

Also what would happen if I wired the speakers wrong, as I thought that may be the prob, but from memory when I did it before nothing happened!

The amp is located on the boot floor at the back on the passenger side, I believe the cable is 18AWG, although it was all already installed when I bought the car. The -ve is connected to the screw on the jack holder, the cable is too short to reach anything else.

The head unit is a Kenwood KRC 394, which I am seriously considering replacing. The amp remote is connected to a red wire, which in turn also has another red and a seperate white wire connected to it. If it can't be remedied I will take the amp out and just live with the front speakers, as I don't fancy taking all the carpet and seats out. Unfortunately working 6 days a week I don't usually have time to work on the car

If I were to go the ICE installer route I would just take it as is, and wait for the bill

Or, if it really comes down to it, I'll buy some more speaker wire and just run them from the head unit!! I had no troubles last time with that, and the only reason I used the amp is that the wiring was already in place!

Thanks again,

Greg

[Dom]

If you do decide you want professional help my flatmate could do it for you as a nice cheap cash job, could you get to Swindon?

[placey]

greg

kenwood use very standard wire colouring for their head units - so behind your krc-394 you should have the following wires joined together: (whether inside a multi-pin plug or not is irrelevant - they just need to be joined together sturdily)

car side - what it is - kenwood side
grey/red - permanent live - yellow
violet - switched live via ignition - red
brown - earth or -ve - black

some people connect the yellow and red wires of the head unit together and then join them to the positive battery terminal so that the head unit can be used independently of the ignition - sounds as though something like that has been done with yours. if you can identify the car loom grey/red and violet wires it's well worth joining them to the kenwood loom as they should be. a multi-meter or fiddling about with a wire and bulb help identify what's going on with current if in any doubt.

as for the amp remote it needs to be connected to the blue/white wire in the kenwood loom. who knows what wire colour the previous installer used to travel the cabin length with.

the only white wire i can think of in the e30 setup is one of the 2 wires (red and white) for the electric aerial. i can't remember which way round these are - but one is a permanent live and the other is the on-signal switch - now i'm guessing that the white cable is the aerial trigger cable and this has been joined to the remote terminal of the amp. if you're running just the one amp then why does this branch off to another red wire as well? it's worth tracing these wires back to find out where they're from. anyways - if you want your aerial to go up and down when you switch the head unit on and off you'll need to connect the trigger wire to the blue/white kenwood wire too - as that kenwood model does not appear to have a separate aerial trigger wire.

i reckon you're well advised to trace back the power cable (+ve) to the amp too and find out where that starts. really this needs to be straight from the battery via 2 fuses - 1 at each end. i wouldn't run an amp from anything else say for example a cigarette lighter - it can draw too much current for too thin a wire.

if you follow all this closely, carefully and make sure it's all fine i reckon you'll be home and dry.

just to answer your sepecific questions - the amp needs 12v at both +ve and remote terminals before it'll switch on. (earthed of course) you won't do any harm bridging the +ve and remote for tesing purposes.

speakers are difficult to wire up incorrectly - just put speaker +ve to amp +ve and speaker -ve to amp -ve. don't connect the speaker -ve to the car earth.

shout us the results!

if you're about for any of the meets this summer i'll quite happily pack some tools and spend a couple of happy hours going through it all....

[Hightower]

I've had the same problem witn my old car, it turned out to be a poor earth on the amplifier, make sure you got good connections on poitive and negative terminals, see if that helps, if not i'll go through some paperwork and see what other faults cause this problem.
Dont be alarmed, I'm a qualified mechanic and I.C.E installer.

[Jos]

The noise is the alternator on the engine. You can filter it off the power cable by putting a reasonable sized capacitor accross the +ve and -ve terminals on your amplifer. Although I have never had to do this. Stiffening capacitors do a nice job of this although are a little overkill.

Run your -ve back to the battery aswell, lots of people just whack it onto the chassis in the boot, it's not really good enough.

Don't run power cables and signal cables together, although its not a huge issue in cars.


Also 18AWG is a little small, it only has a current capacity of about 15amps, most amplifers are a lot more than that. Look at the fuse on the amplifer and see what size it is. You need power cable rated to at least that.

Something around 10AWG would be fine for 1-2 amplifers, it can handle about 50amps or so.

Make sure you put a fuse at the battery end on the +ve rated to the same or less than the cable. If you get a short on the power cable connected to the battery, the cable will melt, possibly catching fire and/or blowing a hole in the bodywork. You don't really need another fuse at the amp end.

[huggybear]

Its most probably a problem with one of your earth connections
try this page for more info

http://www.termpro.com/articles/noise.html

[austinsom]

Cheers for all the info guys! After trying all the tips I still had the noise, so have just run wire from the head unit to the speakers as I just want some sound from the back, not too bothered how it gets there!!

Maybe one day I will put an amp back in!

Thanks again!

Greg