Good forum for diagnosing amp whine?

[GarethRS]

Hi all,

Can anyone recomend a good forum that they use for car av stuff? I have amp whine and have recently tried running a ground wire from the hu to the amp with no effect.

Was thinking of avforums?

Many thanks

[Silversea]

Try www.Talkaudio.co.uk

[no_RS]

When you connected the amp earth to the head unit earth, did you remove any local earth at the amplifier end? Is the amplifier bolted to the car chassis? If so it is worth removing it from the chassis as this is also an earth connection and may help deal with the problem.

[GarethRS]

Hi,

Yes, i removed the existing amp ground lead. I have a saloon and I have mounted my amp under the rear shelf on a piece of MDF, so it's not connected to ground via the chassis either.

I have removed the existing Bose amp and utilized the wiring, so it is using the existing wiring, I find it odd I should get this issue. I also noticed the other day, that I get a slight "whine" when I just turn on the ignition and dont start the engine.

[teknobod]

The amp should be earthed to the car body with as short a lead as possible. Use a suitable guage cable and don't be tempted to use an existing bolt to clamp it under. We always used to clean the paint down to bare metal where the amp would be earthed and use a body bolt.

One thing to check is whether the whine is induced in the amp or in the signal cables to the amp. Remove the RCA input cables and power up the amp. Do you still get any whine?

Just noticed that you've use the existing wiring which may make identifying the problem harder? What brand of amp have you installed, and what power rating is it?

Andy

[GarethRS]

Hi Andy,

I have not tried earthing it to the body yet, i will give that a go.

I have been tempted to running some new rca leads, but i'm reluctant as the existing wires are actually quite a good quality and guage, but may buy some and try just running them through the cabin first.

The amp is a Jbl gto 6000 I brought secondhand. I would be surprised if it was causing the problem, but I wouldn't rule it out. Authough, as already said, i'm using the existing wiring, power and rca as the bose, so i'm surprised to be having an issue.

Thanks for your help.

[teknobod]

Tbh, when fitting something as 'beefy' as that, although I know it will be a right royal PITA, I would suggest totally rewiring. The reason I asked about the amp brand was some of the budget amps can suffer from whine that it is very difficult to totally eliminate. The JBL unit should be ok.

I haven't seen the stock wiring for the Bose amp but I suspect that it will not be adequate to supply the required power to the JBL.

I know that you didn't have any problems with the Bose setup as far as the whine, but the only way to truly eliminate the wiring would be to run dedicated power and signal cables for the JBL (and run them separately - best practice). Just as an aside, are you using the stock head unit? Are you using the standard speakers? I have seen problems before when trying to mate aftermarket amps to stock head units.

Andy

[GarethRS]

Hi Andy,

I'm running a Kenwood dnx 5240bt hu and infinity reference speakers.

Ok, here's my plan;

As the battery is in the boot of the RS6, I can run a new fused large gauge power and earth from the battery to the amp. Then run new RCA leads to the HU along with a suitable sized ground. I was going to leave the exist HU power and amp switch (the blue wire). Was thinking it maybe better to buy a reel of RCA cable and make my own leads. I'm fairly able with a soldering iron and I could make the leads the correct length.

Please correct me if I'm wrong.

Thanks again

[teknobod]

Hi Andy,

As the battery is in the boot of the RS6

That makes the job a whole lot easier!

I would definitely run a fused cable from the battery for power, but not the earth. Make the earth cable as short as possible and connect to the car body using a separate bolt ( As I said before not under an existing bolt such as seat mountings which seems to be a favourite!)

If you can make up RCA leads, it is much better to have them the correct length so you're not having to coil up any excess (Use good quality cable) and do not run it near any power cables which will most certainly be in one or both sill channels with the battery being in the boot.
Down the centre of the car is usually a good idea. You could use the existing wire for the amp switching as it is only a low current switch, but if this is also shared for the antenna booster, you may be better running a new wire (you'll be running new RCA's from the head unit so just run it with them). Finally, I would also run new speaker cables if you haven't already done so.

To save yourself a lot grief, before running the RCA's, connect power and earth to the amp with the speakers connected, and bridge a small fused cable from the +ve power terminal to the amp switching terminal to turn on the amp. Make sure that you don't have any whine through the speakers at this point (check with key on too, plus engine running to be sure). If everything is still ok, then continue with installing the RCA's.

You shouldn't need to run a separate ground between amp and head unit, as they should both already be grounded. One other thing to check now I've had chance to think about it. Make sure that the head unit has its own dedicated earth. I've seen problems before where the head unit loses it's dedicated earth but still manages to take an earth through the mounting brackets or from the aerial cable shield which can also introduce problems!

Once this is all done, Robert is indeed your mother's brother as they say.
Enjoy the fruits of all your hard work, I'm sure you'll find it was worthwhile doing it properly.


Andy

[GarethRS]

Hi Andy,

Whats your opinion on RCA cables. Just been looking on the Maplin web site. I've heard two schools of thought. One is to use good screened cable with the screen as the ground or -, another thought is to use twin core screened. Been looking at the latter.

Also, I'd rather not replace the speaker wire as that would be a real pain in the bottom as I will have to remove all the door panels. Do you think this high level outputs could cause "whine".

Many thanks for your help

[no_RS]

For the RCA cable I would use the first option, the twin core screened cable implies the amp input is for a balanced signal which it is not. The speaker wires probably do not need changing unless you are running a high power amp, as to whether the high level output is causing the whine. I doubt it as it doesn't take much noise at the input to create the problem, suggest you disconnect the input RCA's (at the amp) and power/enable the amp and listen, no noise means the problem is related to the RCA's input.

The whine you are experiencing, does the pitch change with engine rev's or is a steady pitch, have you tried turning off any accessories you may have on?

[GarethRS]

Hi ya,

Yes, it does change pitch when the engine rev's rise and fall, but I did notice it slighly with the ignition on and engine not running.

I will have a play with the rca leads. I suspect them to be honest, but I find it difficult to understand why the problem didn't exist on the Bose setup as it the same wiring.

I plan to pop to Maplin's this week and wil pick up the necessary to make some RCA leads.

thx

[teknobod]

The speaker wires probably do not need changing unless you are running a high power amp

Have you looked at the spec's on the JBL amp he's fitted?

Class : AB
Max Power : 1100W
RMS Power @ 4Ohms : 4X50W + 2x75W
RMS Power @ 2Ohms : 4X75W + 2x125W
RMS Bridged : 2x150W + 250W
Freq. Response : 10Hz - 40kHz
THD : 0.1%
S/N Ratio : >92
Bass Boost : +6dB @ 45Hz
Crossover : Ch 1/2, 3/4: Flat/HP; Ch 5/6: Flat/LP
Variable : 30Hz - 320Hz
Slope : 12 dB/oct.
Input sensitivity : 250mV - 4V
Dimensions (WxHxL) : 568 x 55 x 294 mm

I wasn't suggesting changing the speaker cables to eliminate the whine, by the way, which is why I'd previously mentioned disconnecting the signal inputs.

Some OE installations also share speaker negatives between left/right or front/rear which can upset aftermarket amps.

Gareth, I would agree with no_rs re the RCA's.

Andy

[GarethRS]

Hi,

I did an experiment today.

I unplugged the rca cables from the amp, no noise either when the engine was running or just the ignition on (apart from a hiss)

Connected the rca's back into the amp and unplugged from the HU, lots of noise and 100% more whine with engine on or off.

I have ordered 12 meters of cable and connectors from Maplin today, so i'll see when happens after I have installed that.

thanks.

[no_RS]

One check worth making is to measure the resistance using a multimeter between the outer RCA connection on the amp and the amp body, measure both amps to see if they are the same. My suspicion is that ground noise is getting coupled into the input of the amp due to different circuits in the amp and wiring changes.

When the BOSE amp was fitted, how did this get power, was it powered directly from the battery or via the loom. If it was powered via the loom can you power the new amp using the same wiring/connections that the BOSE amp used and see if that is quiet then try making one change at a time to see to what affect it has. The car manufacturers spend a lot of time making sure everything works and changes to amps, wiring etc can cause lot of headaches. Electromagnetic compatibility is a real PITA, just ask Toyota (though they will deny it and say it is a sticky throttle).