Good forum for diagnosing amp whine?

[teknobod]

Hi,

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).

I think that pretty much identifies the problem Gareth. Sorted!

Andy

[PetrolDave]

Sounds like a ground loop to me - try connecting the RCA inners and not the outers.

[GarethRS]

Sounds like a ground loop to me - try connecting the RCA inners and not the outers.

Tried that, with only one rca connected, no difference.

I've now run the new rca leads front to back and a single power for the amp switch to save me cutting the HU plug. I hope to terminate the leads tomorrow and plug them them in to see what happens. Fingers crossed.

I was thinking like I do, the stand cables have a shared ground, i.e there are only five multi cored wires. Maybe this is the problem and the bose amp is wired different. I will hopefully find out tomorrow.

[PetrolDave]

I was thinking like I do, the stand cables have a shared ground, i.e there are only five multi cored wires. Maybe this is the problem and the bose amp is wired different. I will hopefully find out tomorrow.

The line out from Audi head units is 5 wires - 4 signal plus a common audio ground.

[GarethRS]

Guys,

I have run the cables using double insulated cable and I soldered the RCA connectors on this afternoon. I hope to get into the garage tonight when my kids are in bed to hook it all up and see if it works.

[teknobod]

Don't use the factory speaker wires if they are a shared signal earth. (I think I may have mentioned this in an earlier post!) Could damage the amp depending on the output configuration.

Andy

[GarethRS]

Hi all,

Well, changing the RCA leads did not fix my issue, it's reduced, but still there, grrr.

Ok, i'll summerise what I have;

Kenwood DNX5140bt HU (also used my old Alpine and OEM RNS-D)
New RCA cables from front and rear
JBL GTO6000 amp
Existing speaker wires (did buzz them out end to end so I know which one is which and no common ground)
Infinity 6510cs speakers with crossover

I have now wired the Amp to the chassis using a new bolt and making sure all the paint is removed.

Without changing the speaker wire (i'd be staggard if that was the issue, but wont rule it out, it's just a pain in the xxx to change), the only thing I could think of left is to ground the HU to the chassis.

It could be an Amp fault, anyone seen this before?

Many thanks

[teknobod]

I don't think it's an amp fault gareth because removing the RCA's would not have made any difference.

As has been said earlier, you're either picking up some noise induced into the RCA cables or the problem is at the head unit end, although I rather suspect this not to be the case if 3 different head units all exhibit the same problem. (Unless of course the H/U earth is not good)

I'm scratching my head a bit on this one. Let me have a think about the setup. (With the amp powered up and no RCA's connected, there's definitely no noise?)

Andy

[GarethRS]

Hi Andy,

I've just been down to my car in my works carpark to have a try.

Ok, this is what I did;

1. Pulled out HU onto my lap (thinking, before I pull the rca's, i'll start it up and try)
2. Start engine and listen - nothing, no whine.
3. Hmm, push HU back into dash, still no whine.
4. Pulled RCA's, nothing, replaced RCA's nothing.
5. Had a play with the ground connections, established I had 3. (FM antenna, chassis and wiring [the black one lead])

When I drove to work this morning, I definitely had whine.

I'm wondering if I have a doggy HU ground. Doesn't explain why on the old RCA's I got whine when I removed them from the HU apart from that lead had a common, grounded conenction for all channels. That wiring is still there, so I could try it again.

Plot thickens...

[T2FOO]

Do you have a hands-free car kit?

I had a problem like that, on my old S4, it went away when I changed from a Nokia kit to a Parrott.

[GarethRS]

Hi, no hands free kits any more, just in HU built in Parrott.

Today I have run a new earth to the HU from the chassis, whine still there, grrr.

[teknobod]

Gareth,

Just a quick reply to say that I've not forgotten about this but I'm snowed under with work at the moment.

I will come back to you when I get chance to thik about it some more.

Andy

[GarethRS]

Hi Andy,

I haven't been using my car as I've dusted my bike off and been using that.
Many thanks for your continued help.

Gareth

[GarethRS]

Hi guys,

Sorry to rake up an old thread, but i've not been using my car until today.

I've just had a further play and have found the following;

Whine still there, it changes with rev's but does not increase with volume, i.e if I increase the HU volume.
If I pull out all the RCA's, there is a loud whine, plugging them back in and it goes and then slowly comes back.
Tried pulling out the fm antenna incase it was a dodgy ground, no difference.

I have since connected both the amp and the HU to a dedicated ground chassis point and not used the vehicle ground connection. No change.

Could my amp be duff? it was secondhand..
The only think I havent changed now is the speaker wire which is a bit of a pain, but it good quality.


many thanks
Gareth

[PetrolDave]

The only think I havent changed now is the speaker wire which is a bit of a pain, but it good quality.

The speaker connection is high power & low impedance - IMHO the chance of whine getting in through that route is pretty close to zero.