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Noise through speakers related to engine speed?

Old 03-11-2012, 03:06 PM
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Noise through speakers related to engine speed?

I just installed an amplifier so that my speakers aren't powered by the deck any more. I've noticed an audible buzzing/crackling sound through the speakers while the engine is running and it increases as RPM increases, quitting completely when vehicle is just on accessory power with the engine off. I have 2 sets of RCAs, each having a ground wire built in.

I should note that I have had a subwoofer amplifier connected for some time now and I've never heard this noise through my subs.


Here's how my system is set up:

Head Unit has 3 sets of RCAs going to the back of the truck, one for sub amp and two for the 4 channel speaker amp.

Power wire is 2Ga which goes to a bus in the rear of the truck and is split off from there.

I've grounded each end of each set of RCAs to the chassis.

Power wire is on one side of the vehicle, all the other wires run down the other side.


Sub amp: Audison LRX 1.1k
Subs: Hertz HX250D

Speaker Amp: Pioneer Premier GM-X1040
Speakers are some Kenwood 4x6`s all the way around, not sure of the model

Inline 80A fuse protecting the power wire.

Can anyone help me to identify this problem and possibly correct it?

Thanks in advance.

-Tyler
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Old 03-12-2012, 07:14 AM
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Sure sounds like a ground loop issue so I would recheck all of the grounds, make sure they are tight and on non-painted surfaces and at a significant point in the vehicle structure. If the preamp cables cross the power lines at any point, try to make sure they cross as close to 90 deg as possible. Make sure the engine to chassis & to body ground wires are still there and functioning (tight and clean). Beyond that you may have to look at adding a filter unless someone else has some more ideas.
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Old 03-12-2012, 08:36 PM
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Well I sorted some of it out....

First, I realized my aftermarket tach was sharing the same ground wire as my head unit and the RCAs so I gave it its own ground

Second, I took the ground wires from the RCAs and with a ring terminal attached them to the chassis of the head unit

I told the car audio shop in town about my problem and he said he would bet money that it was bad RCAs. He loaned me a set of Audison high quality ones to test with and the noise was actually worse with these, so back to the shop they go.

Also, the manager at the shop said that engine related noise is notorious in Chevys, which is what I drive (1992 GMC Sierra). Not sure if this is bull or not but I thought I'd throw that out there.

So after moving the RCA ground to the head unit chassis the noise is noticeably quieter but it is still there.

I only ever notice it now with the music off but that's not the point, it shouldn't make noise at all, I like my things to work correctly. :P

Also I've been doing a considerable amount of research on these ground loop isolation devices and filters that go in the RCA line but everything I've read states that sound quality is compromised when such items are used.

Anyone have any other thoughts regarding this issue?
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Old 03-12-2012, 10:02 PM
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have you tried using shielded interconnects, or interconnects with a drain wire, you can also try ferrite beads close to each end of the wire length close to the connector
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Old 03-13-2012, 01:19 AM
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The Audison RCAs that the dealer loaned me were shielded and made no positive difference. How would I go about putting a ferrite bead in-line? Never heard of that strategy before.
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Old 03-13-2012, 07:40 AM
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ferrite beads are a ceramic/iron mixture, if you look at your computer peripherals (mice/keyboards/monitors) the got a cylinder looking piece of plastic close to the connector, they sell these in different shapes and sizes, since the interconnects have a wider connector than the cable itself you have to get a clamshell type which you snap over the cable and lock into place
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Old 03-13-2012, 09:41 PM
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Where are your gains at? Sometimes to get rid of that last bit of whine you need to lower them just a bit.

As for RCA ground loop isolators - generally they affect the bass which your 4x6s are not doing anyway and decent ones don't muck up the signal too much.
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Old 03-14-2012, 03:37 PM
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I'll defintely have a second look at the gains and see if I can get rid of the noise that way, and if not then I'll try out one of those ground loop isolators. The source has one on for like 20 dollars and if it doesn't work I will just return it.

As for the ferrite bead, I'm not sure I want to get that far into this as it seems like a fair bit of work to install those things in the RCA cables
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Old 03-14-2012, 09:54 PM
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So I talked to the head guy at the audio shop, (he wasn't there when I went before) and he said that old amps like this tend to be sensitive to a voltage difference between the amp and the deck. So I changed the deck ground to the same spot that the amp is grounded to.

No luck!

Kind of frustrating because running wire to the back of the vehicle isn't the easiest thing in the world but I guess the factory ground on the deck was probably high resistance anyways.

I'm thrown for a loop here... not sure what to try next... might actually try and get the Hertz HE4 sometime in the near future to replace the Pioneer because I have a sneaking suspicion that the amp is the culprit...
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Old 03-14-2012, 10:28 PM
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And as for the ferrite bead... I now know that they actually nap over the wire, I just assumed that you had to somehow wire it inline :P

Where can I get my hands on these ferrite beads?

Last edited by masterelyt; 03-14-2012 at 10:57 PM.
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