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post #11 of 18 (permalink) Old 08-13-2009, 05:29 PM Thread Starter
 
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Sorry for not replying in so long. I subscribed to this thread but got absolutely no emails, so I thought nobody had any help. :-P Let me address each issue and also update one what I've found. Thanks EVERYBODY for the tips! This has been a most interesting read!!

John H - The amp is in a very thick and heavy metal case. It's an Orion XTR5004. Orion makes REALLY good stuff. I've been brand loyal for 15 years. :-D It's sitting up against the engine compartment, behind the passenger seat, but I have moved it around to different positions - no change.

Joey - If by the skinny wire, you mean the amp turn-on wire, then yes, it is run down the same "channel" under the carpet as the power wire. I'll try moving it to the side of the RCA cables. I should note the RCA is over two feet away from the power wire, which I know is recommended. Also, the "chatter" is still audible even when the RCAs are unplugged.

piglith - It may be a ground loop, but it's not digital cell phone chatter. I can enduce the digital chatter by moving the shifter from N to D and back. It's exact and always happens when I do that. It happens at other random intervals, which is how I inferred the possibility that other aspects of the Smart's control systems may chatter themselves. I am very convinced the chatter is due to a data bus that the Smart uses and not something like a cell phone or other external factor.

PerryA - If anybody can dig up a wiring diagram, that'd be so awesome. I am not using shielded (coaxial style) RCA cables. I'm using twisted pair style, which from what I've read, is better at reducing noise than shielded RCA. For the heck of it, I tried a coaxial RCA cable and had the same results.

Now for updates... Maybe somebody will have other ideas?

1. I ran my head unit's ground to the same grounding point as my amp. I'm using the bolt that's sticking out over the engine compartment carpet. (It's bare metal and a resistence reading with a voltmeter showed it to be a good ground.) This reduced the noise somewhat. Also, it seemed I did have a little alternator whine afterall initially, but it wasn't much as I only noticed it when it was gone, not when it was on. :-) Anyway, the digital chatter is still there, but it is less.

2. As stated above, I've tried various RCAs with no difference.

Some thoughts...

I'm thinking that the sound is either leaking in through the ground point or the power cable itself.

The ferrite is an excellent idea. I'm going to try wrapping it around the power and ground wires. Does it matter where I place it? At the end I would assume... Both ends maybe?

I wonder if 4 AWG wire would help? (currently using 8 AWG Monster)

Does anybody else have a good suggestion for a ground point? Would it be safe to run the ground for the amp directly to the battery? Afterall, in a Smart, that's a pretty short path (less than three feet from where my amp is now)! Could a direct battery ground be noiser? I read somewhere that direct battery grounds can sometimes be noisey.

Matching the head unit and amp ground to the same point is a start, but I'm not finished! :-)
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post #12 of 18 (permalink) Old 08-13-2009, 06:22 PM
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The ferrite is an excellent idea. I'm going to try wrapping it around the power and ground wires. Does it matter where I place it? At the end I would assume... Both ends maybe?
Glad you came back to check!

The ferrite is most effective at the entry to your amp. If you've already unplugged the inputs and you still hear the whine, then you only need to concentrate on the power and the speaker cables, not the inputs (at this point, at least). The noise on any entry into the amplifier can cause problems on the input circuit. The ferrites will cut the noise down as the wires pass through the center; the closer they are to the amp the less possibility you have of introducing more noise.

Your speakers are completely isolated from the car ground, right?

Good luck!
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post #13 of 18 (permalink) Old 08-19-2009, 12:20 PM Thread Starter
 
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Glad you came back to check!

The ferrite is most effective at the entry to your amp. If you've already unplugged the inputs and you still hear the whine, ...
The whine/digital distortion is still there when the RCAs are unplugged, BUT it's quieter. Does that mean anything?

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...then you only need to concentrate on the power and the speaker cables, not the inputs (at this point, at least). The noise on any entry into the amplifier can cause problems on the input circuit. The ferrites will cut the noise down as the wires pass through the center; the closer they are to the amp the less possibility you have of introducing more noise.
Thanks for the tip. I ordered a couple different ferrites and I'm going to try them on different cables one at a time to see what happens.

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Your speakers are completely isolated from the car ground, right?
Good luck!
I would imagine so because the mounting area in the doors is completely plastic. The only way an electrical ground could be made on the speakers there would be over the speaker wire, which would introduce a lot of analog distortion, which I don't have, not to mention it'd make my amp hot and unhappy from the short. ;-)

Since my last post, I have done the following:

- Replaced the 8 AWG amp ground with 4 AWG ground.
- Grounded the amp directly to the battery (along with the head unit's ground).

Neither had any effect, but the wiring is a lot cleaner looking going to the battery instead of the bolt in the luggage area.

Oh before anybody complains about grounding to the battery, there is nothing electrically wrong with it in a smart because the ground cable is still really short since the battery is in the foot well. Additionally, there is no noise increase from my doing that. It can be noisier, especially with a LONG cable in a typical car. If I was starting with that set up, I would definitely try a different grounding point first before posting. Anyway, just wanted to clear that up because I can already hear somebody fixing to type "don't ground to battery - NOISEY!" :-D
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post #14 of 18 (permalink) Old 08-20-2009, 08:50 AM
 
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did you rout any of the cables down the center of the car you didd mention when you shift the shifter it does it. maybe the wires are being disrupted when you shift or when you drive. does is still do it when ur not moveing?
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post #15 of 18 (permalink) Old 03-08-2010, 01:53 AM
 
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just upgraded my system, I have the same problem too

everytime I put I foot on the gas paddle the sound became louder.......

what should I do ?
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post #16 of 18 (permalink) Old 03-08-2010, 05:33 AM
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just upgraded my system, I have the same problem too

everytime I put I foot on the gas paddle the sound became louder.......

what should I do ?
Read this thread?
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post #17 of 18 (permalink) Old 03-08-2010, 05:41 AM
 
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Trying to think outside the box... how is your amp attached to the car? it could be introducing noise that way if you bolted it to metal... a grounded part!
another possible noise leak could be the Blue wire (amp on 12v) try disconnecting it and using a 12v external input to turn the amp on.. hey it might be a dirty 12v from the radio...
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post #18 of 18 (permalink) Old 03-08-2010, 05:59 AM Thread Starter
 
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just upgraded my system, I have the same problem too

everytime I put I foot on the gas paddle the sound became louder.......

what should I do ?

Your problem sounds like classic 'alternator whine" -- especially since it gets louder as you accelerate. I'll guess it also changes pitch as you accelerate and when the car shifts.

Do a google for "alternator whine" and you will find a bazillion troubleshooting guides.

As for my original problem. Here's how I resolved it (sorry I never replied to this post).

1. I moved the amp to under the passenger seat, instead of leaning against the engine compartment. A lot of the noise was being directly induced in the amp, but I couldn't hear it until I plugged in the RCAs. I'm guessing it's a combination of induction noise from computer cables with a ground loop here. I'm not sure. Again, my issue was "digital chatter" and not plain old engine whine. This eliminated about 50% of the noise.

2. I turned up the pre-amp on my head unit and turned down the gain on the amp. This eliminated about 25% more noise.

3. I installed an RCA noise filter (magnetically coupled) with the coupling as close to the amp as possible. I was then free to run the RCA any way I wanted, because any inducted noise on the RCA would be eliminated at that point. I was shocked at how good these things sound now. In the past, you would hear a perceptible drop in high frequencies. I A/Bed this thing (just a generic one I got at a local car stereo shop) and I can't tell the difference. Good enough for me. I could probably undo step #2, but I just haven't gotten around to it.

For those looking, here's a bunch...
rca noise filter - Google Product Search

One thing I didn't try, but was planning to if #3 didn't work was pulling up the carpet on the passenger side near the amp (under the seat and towards the engine compartment) and lining it with mumetal or some other similar RF shield. I've had good luck eliminating A/C whine (of the 60Hz variety) with that stuff before.
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