Noise coming in on Mach460/aftermarket HU

[Chris_Red_V8]

I've never had this problem before, and I'll start by saying these magical words:

I just redid the harness (so I could solder all connections and use shrink wrap, before it was really ghetto).

I have a mach 460 with a Alpine 9813 headunit. The mach is being driven off the headunit's 4V preamp outs for front and rear. The sub outs go to a A/D converter and are sent back to a amp and sub setup.

Anyways, my problem is this: I can hear a static that's in the pattern of the motor firing at all speeds. Its sometimes quieter once I'm cruising, but it sounds very similar to a small header leak I have (pft pft pft type deal).

So where can ingress noise be coming from? Bad ground? I've rechecked my harness, all the connections are good, there are a set of gauges below the headunit, and I know those long thin wires could carry noise back, and I believe they share a ground.

Thoughts? This thing drives me nuts.

 

[mixedbreed02gt]

you have a ground loop somewhere in the wiring. get on ebay and order a ground loop isolator, plug in between the rca's and the head unit, should resolve your noise.

 

[Chris_Red_V8]

I did disconnect the rca's, and while the mach amps were still on, the noise was still present. With the RCA's disconnected, would a ground loop still show that noise?

 

[Speedracer06288]

are you using a amp intergrated harness?

 

[Chris_Red_V8]

I believe so.

Basically my connections look like this:

MAch harness 1 (power and related) -> adapter harness from crutchfield to alpine harness

Mach harness 2 (small audio data) - > adapter to 4 RCA inputs -> FL FR RR RL alpine RCA outs.

then the mach loop harness is correctly connected.


When I disconnect harness 2, and leave harness one connected (IE amp turn on lead is powered), the noise is still there.

 

[mixedbreed02gt]

I did disconnect the rca's, and while the mach amps were still on, the noise was still present. With the RCA's disconnected, would a ground loop still show that noise?

yeah you can still have a ground loop. I was hoping it would be between the amp and the head unit because that's where most ground loops exist. so somewhere you have a ground connection that is not secure. be it a speaker wire connection, a bad ground wire connected at a harness plug, could be your vehicle or battery ground is loose or corroded, possibilities are endless.

best thing I can tell you would be to take it to a car audio installation (NOT BEST BUY OR CIRCUIT CITY) but a custom installer that does it professionally, and have them search for it...will probably run you about $60 an hour for labor, but if anyone can find it they can. ground loops are a pita to find, but easy to fix once you find them.

 

[mixedbreed02gt]

I believe so.

Basically my connections look like this:

MAch harness 1 (power and related) -> adapter harness from crutchfield to alpine harness

Mach harness 2 (small audio data) - > adapter to 4 RCA inputs -> FL FR RR RL alpine RCA outs.

then the mach loop harness is correctly connected.


When I disconnect harness 2, and leave harness one connected (IE amp turn on lead is powered), the noise is still there.

well if you disconnect harness 2, and the noise is still there, then it's somewhere in the wiring or harness for harness 1.

I would ground your cd player directly to the chasis instead of to the harness ground and see if that resolves it. it could be very well that the guage ground and the cd ground are interfering with each other.

 

[Chris_Red_V8]

Tested grounding the rca outer terminals, noise worsened and also picked up a faint alternator whine type sound. The overal noise (static) floor lifted up a bit.

Releasing the ground returned it to as before.

Running a new good ground for the headunit made no difference.

Only other change would be a battery relocate and associated wiring, and I removed my sub and amp (still there, just removed the old positive feed since the battery is in the trunk), when I install a master safety switch, I'll repower the amp off of it.

I thought maybe there was grounding issues, the battery has an excellent ground, and the original grounds in the front bay are excellent as well. additional engine ground was added.

Just passing on possibly relevent stuff.

 

[mixedbreed02gt]

well only other thing I can think of is that the head unit is the cause/source of your noise. either that or it has to be somewhere in the main harness.


what is model # of the amp harness you are using that connects the mach 460 to the aftermarket unit?


how new/good are the vehicle to battery ground cables? im assuming from your post above they are good?

 

[Chris_Red_V8]

well only other thing I can think of is that the head unit is the cause/source of your noise. either that or it has to be somewhere in the main harness.


what is model # of the amp harness you are using that connects the mach 460 to the aftermarket unit?


how new/good are the vehicle to battery ground cables? im assuming from your post above they are good?

I'll have to find the harness, but its the crutchfield specified one for the mach460 in 94-04.

Battery ground is pretty good, its mounted to the upper end of the trunk on a large attachment bolt, and I sanded the body down to metal where it attaches.

 

[mixedbreed02gt]

I'll have to find the harness, but its the crutchfield specified one for the mach460 in 94-04.

Battery ground is pretty good, its mounted to the upper end of the trunk on a large attachment bolt, and I sanded the body down to metal where it attaches.

only thing i can think of it's the harness then. I'd suggest taking it to a professional stereo shop and seeing if they can figure it out. it's outta my league.

 

[Speedracer06288]

well, the last thing you can do if you want is bypass the amps. It will reduce the sound some, but at least you have a after market radio pushing out more power. I know all the wireing is already at each speaker. you don't have to run all new wire.

 

[Chris_Red_V8]

well, the last thing you can do if you want is bypass the amps. It will reduce the sound some, but at least you have a after market radio pushing out more power. I know all the wireing is already at each speaker. you don't have to run all new wire.

I'd also have to replace all the speakers, or figure out a way to build a crossover network for each corner pair.

I'll swing it by a stereo shop this week. If they can't figure it out, I'll tear out the harnesses this weekend and do a wire by wire trace.

 

[mixedbreed02gt]

I'd also have to replace all the speakers, or figure out a way to build a crossover network for each corner pair.

I'll swing it by a stereo shop this week. If they can't figure it out, I'll tear out the harnesses this weekend and do a wire by wire trace.

have fun with that. let us know how it goes.

i had good sound in mine until i decided to stick a damn "Ultra Linear 7 band graphic equalizer" in. I like the slider controls I have, but I have a ground loop because of it. bought an isolator, and it got some of it, but I can hear it at low speeds still. need to buy another dash kit and a cd player harness, and a metra harness and rewire it all to get rid of the damn ground loop, tired of hearing that noise.