| Author |
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Jason Vance (Jason)
| | Posted on Tuesday, April 16, 2002 - 12:32 pm: | 
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I just installed two new amps (2 channel and 4 channel) to replace the weak factory units. When the engine is off, I get a squealing noise when the automatic interior light dimmer triggers. When the engine is running, I get a ton of other noise (plus when the blinkers go on, or the fan, or...).
The electrical ground to the amps is good, but I'm not sure about the speaker ground. I did not replace the head unit, so I'm dealing with low-level inputs. I'm currently using a non-shielded wire for the speaker grounds from the head-unit and I think that is where I'm picking up the noise.
Question: is the fabric-like wire cover within the dash shielding the speaker-outputs from the head unit...since the wires are otherwise not shielded (from EMF's anyway)? Would it be best to ditch the common ground and use the speaker grounds that run through the loom?
I know the best advice is to ditch the factory loom and rewire everything but I have everything wired up to this point and I just need to get rid of the noise...hopefully without buying a line-level filter or some other vapor-ware gizmo.
Thanks in advance! |
Paul T. Schram (Paulschram)
| | Posted on Tuesday, April 16, 2002 - 01:21 pm: |
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Here we go again.
You are almost certainly suffering from a ground loop caused by the dissimilar grounding wires you have used. What has happened is that even though you have a number of grounds, due to the different wire types and their differences in intrinsic resistance, the "Ground Potential" at the ends of these "Ground" wires are not at the same ground potential. This difference in ground potential allows the amplification of noise that would otherwise be suppressed by the factory system of grounding. You may also have some problems with the balanced configuration of the factory setup and the likely unbalanced configuration of your amplifiers.
Personally, my suggestion would be to junk everything but the factory wiring. They knew what they were doing when they built it, and got paid a whole lot to do it (Yes, I work for a tier one supplier of interior wiring, although we don't do that here).
Does it really sound enough better to have justified the time, expense and frustration you have incurred?
Just replace the head unit and speakers. You will be much happier, and your stereo will sound much better, much sooner.
Paul T. Schram |
Robert Mann (Oldscout)
| | Posted on Tuesday, April 16, 2002 - 01:35 pm: |
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I had all the same problems you have and I took it to a pro and had him looked at my problems
David Navone is one of the biggest automobile audiophiles in the nation. He spent about an hour looking over my install and told me the LR head unit was a POS and move on.
If you need tech help here is his BB forum:
http://www.carsound.com/ubb/ultimatebb.php?ubb=forum;f=2
and his web page:
http://www.davidnavone.com/ |
Jason Vance (Jason)
| | Posted on Tuesday, April 16, 2002 - 01:43 pm: |
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-edit- |
David Dryden (David914)
| | Posted on Tuesday, April 16, 2002 - 05:47 pm: |
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Jason,
Exactly how do you have the new amps connected to the factory head unit? You are correct that the factory head unit has low (line) level outputs. I had just the opposite setup until recently (Alpine head unit with everything else factory) and had good results. You may have to experiment a little to get rid of the ground loop. Try lifting the signal (NOT power) ground connections to the amps. Let us know what you've got.
David |
Jason Vance (Jason)
| | Posted on Tuesday, April 16, 2002 - 06:27 pm: |
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David,
I was running a common speaker ground (not power ground) using an auxillary wire mounted to the chassis of the head unit. I was doing this under the instructions for the amp-install for high-level outputs (because I didn't know at the time it was actually low-level). I found out the outputs were low-level; I wired the blue, green, yellow, and red wires to the appropriate channels (positive leads) and instead of clipping the grounds off the factory amp and transferring them to the new amps, I wired the auxillary ground to the amps (through the low-level inputs). Lots of noise when engine was running. I then moved the origin of the auxillary wire from the chassis to one of the head-unit's speaker ground outputs. That's where I think the problem is.
Inherently this should work...and when the car is off, everything sounds fantastic. But because the factory outputs off the head unit are routed through some type of shielded encasing, and the auxillary wire is not (it passes from the dash, behind the glove box, past the passenger kick panel and underneath the door sill cover...past all of the electrical components). I'm figuring the aux wire is picking up the noise...like an antenna, and if I drop it and hook up the grounds from the loom, I should be back in shape. If that doesn't work, I'll fiddle with it some more.
I'll update this evening. |
Jason Vance (Jason)
| | Posted on Wednesday, April 17, 2002 - 01:24 am: |
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Problem solved. I removed the jumper auxillary wire I was using for a speaker ground and I clipped the ground wires off the factory amp harness and spliced them into the low-level inputs into the new amps. Interestingly, while four grounds exit the factory head-unit, only two grounds enter the factory amp, so they must splice into each other somewhere in between. Since the jumper had done the exact same role as the ground wires, just following a different path through an E-M battlefield, I am still inclined to believe that EMF's played a role...the factory speaker loom appears to go through a shielded fabric sheath. FWIW, if my wife tries to use her cell phone (even prior to the amp swap) we get the same kind of noise through the speakers, whether the volume is quiet or loud. Cell phones have crazy E-M radiation, but no other auto-audio system I've had has ever done that (stock or aftermarket).
Oh, yeah; results: stock head-unit + crappy stock antenna + cheap aftermarket amps (2 x 50w and 4 x 60w) + 4 Clarion 2-way 4" speakers + 2 Polk 2-way 6.5" speakers = great sound, great bass response, negligible distortion at low or high volume (as long as bass setting is within capability of the 4"ers), crisp highs, and happy wife. Since I'm happy and she's happy, it was worth the effort and relatively minimal costs. Now if I can only find a factory changer without the premium price tag. |
David Dryden (David914)
| | Posted on Wednesday, April 17, 2002 - 08:05 am: |
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Yeah. it's kinda strange how the factory setup uses only two grounds. What's even stranger is the fact that the grounds are both for the left channel (left front & left rear). You'd think it would be either four grounds or one. Anyway, glad to hear you got it working. My next suggestion was going to be using a pair of ground isolation transformers. I've used them with great success. FWIW, you'll find that most problems in car audio are caused by ground loops, and that the shielding on your line level cables is more important for protecting against inductive coupling from long cable runs next to other vehicle wires. Congrats on getting your system up and running!
David |
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