Noise on the amp , help !

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=10125
Printed Date: September 14, 2025 at 10:32 AM

Topic: Noise on the amp , help !

Posted By: jaxman
Subject: Noise on the amp , help !
Date Posted: February 26, 2003 at 3:55 PM

Hello forum.

Here is my problem , maybe somebody can help me.

Just installed a new amplifier and I encountered a problem.
Every worked fine until I turned the engine on.
When the engine it is on I can hear it in the speakers.

I went with 2 pairs of chin cables from the stereo to the amplifier.
The head unit it is a Pioneer DEH – P7400 MP with the following specifications on the preamped outputs.

Preout max output level/output impedance : 2.2V/1k ohm
Subwoofer :
Frequency 50/80/125 Hz
Slope : -18dB/oct
Gain: +/- 12dB
Phase : Normal / Reverse

If I go out only with one chin audio cable from the rear output to the amp and let the amp take the signal to all the channels from 1-2 then the noise it is almost gone but in the moment I connect both chin cables on the subwoofer and rear preamped output the engine noise begins to be loud and very high every time I accelerate the car.

Tried to put a noise filter on the head unit didn’t help.

Tried to change the chin cables with some pretty expensive chin cables with gold plated heads and still didn’t help.

Tried to take power to the head unit directly from the battery , no help.
With the head unit off , chin cables conected to the amp , and the amplifier on (gave a plus 12 to the remote) the noise is still there.

The only thing I didn’t tried it is to change the head unit.

Do you know what can be the problem and how can I solve it ?

Replies:

Posted By: Fred Berge
Date Posted: February 26, 2003 at 4:29 PM

What kind of amp are you running? and where did you
route your power cable? and what's the make of your car?

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crucial

Posted By: esmith69
Date Posted: February 26, 2003 at 6:19 PM

Try turning down the amp's gains and see if that helps at all. Also, make sure the amp has a good grounding point and that all the power/speaker connections are correct. Since you said the problem still happens even with the head unit turned off, it's almost certaintly something with the amp or with the amp's wiring/connections. Make sure the power cable for the amp is not run near the RCA signal cables.

A ground loop isolator in between the head unit's RCA outputs and the amp's RCA inputs might solve your problem but try all the other things first.

Posted By: jaxman
Date Posted: February 27, 2003 at 3:46 AM

I have a Viper 1100.5 Amplifier.
I will check again the RCA cables and the power cable but as I remmeber I went with the RCA cables outised the car so there was like 1 meter distance betwen the power cord and RCA's.
I even tried to go outiside the car with the power cable.

I'll check again and klet you know guys.
Thank you for the help.

Posted By: Jussi
Date Posted: February 27, 2003 at 3:51 AM

What about your amp, where did you installed it? Sometimes it helps when you isolate your amp from cars metalparts... that groundloop could be one reason.

JL

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Installer/Owner

JL-Autosound

Helsinki, FINLAND

Posted By: jaxman
Date Posted: February 27, 2003 at 6:43 AM

The amp is installed on the back of the rear seat.There is no ground connection between the amp and the car.Besides that the "ears" for the screws are plastic.
I haven't tried yet to change the ground to the head unit.

Posted By: thepencil
Date Posted: February 27, 2003 at 8:51 AM

Where do you hear the engine noise? Through the speakers or the sub? Is your ground cable running to the Amp being share with another electrical equipment? Do you have ground cable grounded to the seatbelt bolt?

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Be careful whose advice you buy, but be patient with those who supply it. posted_image

Posted By: Fred Berge
Date Posted: February 27, 2003 at 10:20 AM

What is a Viper? who makes that?

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crucial

Posted By: Fred Berge
Date Posted: February 27, 2003 at 10:26 AM

Just kidding take it to a shop and see what they can do.
or bring it to mine. Grants Pass OR. posted_image

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crucial

Posted By: jaxman
Date Posted: February 27, 2003 at 2:25 PM

Viper is made by Directed Electronics :)
Well , problems solved.

-Replaced all the RCA cables.(runing twisted pairs now)
-Switched sides for the RCA cables and Power cable.
-Replaced the ground on the head unit.
-Shorted the ground to the amplifier.

After I have done all this I started the engine and the noise was GONE !!!
So I don't really know what was the problem but now it is solved.
Thank you all for the support. posted_image

Posted By: esmith69
Date Posted: February 27, 2003 at 3:19 PM

No problem, glad to hear you got it fixed