Strange problem

Toehead · 07-27-2006, 11:31 PM

Let me start off and say that I did search, and my problem is odd in that it is the reverse of any that I could find when searching.

I got rid of all of my speaker noise for the most part. HOWEVER, I get alternator whine when listening to the headunit with the carputer off. If I turn the carputer on, silence. Not a hint of noise, and my amp is turned up.

Specs are as follows:
dell laptop, powered through invertor and ac power supply
sony x-plod craptastic deck.
all monster cable speaker wires/rca's
run to a kenwood 600w amp which powers the speakers.
All audio equipment is run to a common ground (although the deck ground is a bit long... I took it off the chassis and ran it all the way to the back with thick wire, not sure of AWG, to ground in a common spot with everything else in an attempt to get rid of the noise. Didn't make a difference. )

The noise is only with the carputer off. It doesnt matter whether or not the headunit is on, as long as it is plugged in it makes the noise.
The signals are mixed by a simple audio mixer (shielded) which I made on a radioshack board.
I don't think it is my mixer because if the carputer is on, there is absolutely no noise at all.

If I disconnect the RCA's from the deck, the noise also dissapears.

Any ideas?

scott_fx · 07-27-2006, 11:41 PM

Quote: Originally Posted by Toehead

Let me start off and say that I did search, and my problem is odd in that it is the reverse of any that I could find when searching.

I got rid of all of my speaker noise for the most part. HOWEVER, I get alternator whine when listening to the headunit with the carputer off. If I turn the carputer on, silence. Not a hint of noise, and my amp is turned up.

Specs are as follows:
dell laptop, powered through invertor and ac power supply
sony x-plod craptastic deck.
all monster cable speaker wires/rca's
run to a kenwood 600w amp which powers the speakers.
All audio equipment is run to a common ground (although the deck ground is a bit long... I took it off the chassis and ran it all the way to the back with thick wire, not sure of AWG, to ground in a common spot with everything else in an attempt to get rid of the noise. Didn't make a difference. )

The noise is only with the carputer off. It doesnt matter whether or not the headunit is on, as long as it is plugged in it makes the noise.
The signals are mixed by a simple audio mixer (shielded) which I made on a radioshack board.
I don't think it is my mixer because if the carputer is on, there is absolutely no noise at all.

If I disconnect the RCA's from the deck, the noise also dissapears.

Any ideas?

first thing to do to trouble shoot it is disconnect the mixer. wire the h/u straight to the amp and then wire the pc straight to the amp.. do you still have the noise?

Toehead · 07-27-2006, 11:51 PM

nope. Only with both connected does the noise occur.

scott_fx · 07-27-2006, 11:53 PM

Quote: Originally Posted by Toehead

nope. Only with both connected does the noise occur.

then it has something to do with your mixer. i'm not sure how it was built or even how to trouble shoot that... hmmm anyone?

Toehead · 07-27-2006, 11:56 PM

Why then does the noise only happen when the carputer is off? Should I ground the negative prong of the dc power cable which plugs into the laptop? The adapter is powered at all times.

scott_fx · 07-27-2006, 11:58 PM

Quote: Originally Posted by Toehead

Why then does the noise only happen when the carputer is off? Should I ground the negative prong of the dc power cable which plugs into the laptop? The adapter is powered at all times.

just a stab in the dark but it seems as though the mixer needs two active inputs. do you have an mp3 player? try removing the laptop and plugging in the mp3 play ro the mixer see if you get the same results that you did with the laptop plugged in

Toehead · 07-28-2006, 12:07 AM

Will try. Thanks for the tips, keep em coming.

Toehead · 07-28-2006, 12:20 AM

Nope, no whine when connected to a battery powered mp3 player directly.

scott_fx · 07-28-2006, 12:27 AM

Quote: Originally Posted by Toehead

Nope, no whine when connected to a battery powered mp3 player directly.

just to get it straight you had the mp3 player and the radio hooked up to the mixer, correct?

Toehead · 07-28-2006, 12:29 AM

no i had the carputer and the mp3 player hooked up....

scott_fx · 07-28-2006, 12:38 AM

shouldn't make a difference but try the mp3 player and radio

Toehead · 07-28-2006, 01:16 AM

same result. Thanks for you help though, I appreciate it

Keep the ideas coming!

scott_fx · 07-28-2006, 01:36 AM

Quote: Originally Posted by Toehead

same result. Thanks for you help though, I appreciate it

Keep the ideas coming!

fill in this chart here:
radio directly to the amp = no noise
computer directly to the amp = no noise
radio + computer (on) + mixer = no noise
radio + computer (off) + mixer = noise
alt. source + computer (on) + mixer = ??
alt. source + computer (off) + mixer = ??
radio + alt source (on) + mixer = ??
radio + alt source (off) + mixer = ??

Toehead · 07-28-2006, 09:49 AM

radio directly to the amp = no noise
computer directly to the amp = no noise
radio + computer (on) + mixer = no noise
radio + computer (off) + mixer = noise
computer(off)+radio(off)=noise
alt. source + computer (on) + mixer = no noise
alt. source + computer (off) + mixer = no noise
radio + alt source (on) + mixer = no noise
radio + alt source (off) + mixer = no noise.

Will Albers · 07-29-2006, 10:14 AM

A lot of sound cards will switch their outputs to ground when not powered. This causes the ground loop you hear. Thats why many people look for delayed turn on with their amps while the PC powers up. Its completely normal.

I went optical just to avoid it.

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