Ground Loop Problem

[teknorpi]

I just installed my old amp and sub in the back of the Audi and I am having a horrible alternator whine coming from my tweeters.

Info:

Amp MTX 421D
Sub MTX 8104
Wires are all 4 gauge

The RCA's going to the amp are from the line-inputs and are ground to the two line-input grounds. All connections are soldered.

A couple things that I have troubleshooted.

The tweeters are noisy with HU off.
The noise is not affected by volume.
The noise increases with speed.
The noise goes away when the RCA's are pulled from my amp.
The gain on the amp has no affect on the noise
I checked the amp-ground and it is connected to bare metal.

I have never experienced a ground-loop problem in all the cars I have done in the past, so I need help figuring this out.

[Buttafuoco]

Try grounding the amp directly to your battery first...that will tell you if you have a ground loop isssue.

It could also be due to cross-coupling between your signal (RCA) wires and power cables. Did you run your RCA cables alongside your PWR and/or GND wires?

[teknorpi]

I grounded the amp to the battery, same noise.

The power and ground cables are no where near the RCA cables.

[bcramer]

If you don't get sufficient help here then head over to www.diymobileaudio.com/forum and ask those guys...they know what's up.

Here are a few quick steps that we tell to people over vwvortex.

Steps to solving noise:
1) Set boost and gains to 0.
2) unplug the rcas from the amplifier.
- if noise doesn't stop, reground the amplifier
- if noise doesn't stop, unplug speaker wires one at a time (leave power wires), the wire with a short will will stop the noise when you unplug it
3) If noise stops:
- replace the rcas
- if noise doesn't stop, reground the head unit
- if noise doesn't stop, ground the rcas (strip about three inches of wire and wrap it around the outside metal of the rca connectors, then run to the screw on the back of the head unit
- if noise doesn't stop, replace the head unit

I hope this helps.

[Phrost]

What did you run your RCS's next to the power wire? You sound pretty experienced, but you never know what you can forget

[bcramer]

I grounded the amp to the battery, same noise.

The power and ground cables are no where near the RCA cables.

What did you run your RCS's next to the power wire? You sound pretty experienced, but you never know what you can forget

Reading FTW :)

[Phrost]

Reading is For The Weak ;)

[teknorpi]

Thanks bcramer

Steps to solving noise:
1) Set boost and gains to 0. has no affect on the buzzing
2) unplug the rcas from the amplifier. noise stops immediately
- if noise doesn't stop, reground the amplifier
- if noise doesn't stop, unplug speaker wires one at a time (leave power wires), the wire with a short will will stop the noise when you unplug it
3) If noise stops:
- replace the rcas If the rcas are bad, bringing them in close proximity to a varying power supply should increase the buzzing right? So if it doesn't it shouldn't be the rca's.
- if noise doesn't stop, reground the head unit I guess I should buy the removal keys
- if noise doesn't stop, ground the rcas (strip about three inches of wire and wrap it around the outside metal of the rca connectors, then run to the screw on the back of the head unit what gauge wire should I use for this?
- if noise doesn't stop, replace the head unit Hopefully I don't have to do this as it was just replaced at Christmas time


I have another amp in my other car. I might try that amp to see if I still get the buzzing.

When the buzzing is caused by the rcas can you route the rca-ground to somewhere other than the line-input grounds?

[bcramer]

Tek-

I'll answer your questions as best I can.

If the RCAs are bad, then in theory, if you bring them closer to a power supply should increase the buzzing. I'm not sure if this would be a noticeable amount or not...

I automattically assumed you were using the stock head unit as you didn't list one in your original post and apparently that's not the case. I would definitely reground your head unit and if that doesn't work do ground it on a screw on the back. You don't need any big wiring for this, 14 or 16 should work fine. If your unit is a Pioneer they are notorious for noise...I can tell you more about that later.

Definitely try the other amp, although I doubt it will have any different results.

The last question. Yes you can ground the RCAs.
1. Strip 1-2 inches of insulation/jacket
2. Wrap that around the RCA terminal on the head unit side
3. Use electrical tape to hold it in place.
4. Ground the other end of the wire in the same place you grounded your head unit. Be sure this is a good ground first though.

[Postman]

If you don't get sufficient help here then head over to www.diymobileaudio.com/forum and ask those guys...they know what's up.

Here are a few quick steps that we tell to people over vwvortex.


- if noise doesn't stop, unplug speaker wires one at a time (leave power .

Are you saying a GL can have something to do with speaker wires or did you mean RCAs?
I've never heard of that, but would help explain a strange and inconsistent GL I've been fighting in my A4.

[teknorpi]

Tek-

I'll answer your questions as best I can.

If the RCAs are bad, then in theory, if you bring them closer to a power supply should increase the buzzing. I'm not sure if this would be a noticeable amount or not...

I automattically assumed you were using the stock head unit as you didn't list one in your original post and apparently that's not the case. I would definitely reground your head unit and if that doesn't work do ground it on a screw on the back. You don't need any big wiring for this, 14 or 16 should work fine. If your unit is a Pioneer they are notorious for noise...I can tell you more about that later.

Definitely try the other amp, although I doubt it will have any different results.

The last question. Yes you can ground the RCAs.
1. Strip 1-2 inches of insulation/jacket
2. Wrap that around the RCA terminal on the head unit side
3. Use electrical tape to hold it in place.
4. Ground the other end of the wire in the same place you grounded your head unit. Be sure this is a good ground first though.

I have a stock HU, it was replaced under warranty since the other one didn't work in cold weather.

I'll try grounding the rca's to the headunit as soon as I can get some removal keys.

There are three grounds coming off the factory amp. 2 line-input grounds and 1 amp ground. If I connect the rca grounds to the amp ground that should keep the grounds from the factory speakers away from my rca ground.


On a side note. I listened to the speakers with the sub and rcas disconnected - and there is definitely a small hum coming from the speakers. So maybe there already is a ground problem and adding a sub just makes it worse.

[bcramer]

Any updates on this tek?

[slingblade]

Did they reground the head unit right when they replaced it?