Noise from high level inputs to amp - HELP!!!

[we350z]

I just hooked up my new MTX TA5302 amp by tapping the high level inputs from my stock 2000 X5 4.4i non-dsp Harmon Kardon amp. I followed the DIY on the home page, very helpful I must say Had some problems at first where some loose cables in the wire tap ins were causing a ton of noise in the signal. So much so that my amp was not powering on when using SMART engage LOC (powers on amp from line level input voltage in lieu of 12V remote).

I was able to fix this somewhat by reclamping one of the wires. Though I could still here some line noise when plugging the RCA's into my bookshelf system with volume on high - even with the car off. I plugged them into the amp and it fired right up. For the most part it sounds pretty good. Really fills in the lack of low-end generated by the stock system.

I do hear noise from the sub still tho, even with the head unit volume turned down all the way or OFF. It also has alternator whine when I rev the engine. Almost every amped system I have ever had has had this problem. Usually moving the inputs away from power sources helped. This doesn't seem to be doing me any good in this case. My sub amp is grounded at chassis near passenger tail light. What are some other tips for reducing or elimnating noise?

I've heard:

1) Seperate RCA's (does this mean each -/+ for each or just L/R?)
2) Use ground loop isolator RCA filter
3) Float ground (what does this mean?)
4) Ground HU shroud
5) Avoid running inputs by power sources.

Thanks Guys!

[we350z]

What about grounding my sub amp to the stock amp ground? Also I searched a little and saw some reccomending trying the negative batt terminal.

Thing that gets me is that the noise is present with radio off, and when the entire vehicle is off.

[we350z]

anyone?

[mrbmwx5]

ground your amp to the car body and run your RCA jack seperated away from the power line and add the noise filter to the RAC jack.( for me i did get the power straight from the bettery and just tapp the high input and the remote signal to the stock amp) = no engine noise.

Thing that gets you is that the noise is present with radio off, and when the entire vehicle is off.= you have tapped wrong wire for remote

[we350z]

I am not using a remote wire, this amp uses MTX's Smart Engage technology that sense power from the high level input lines and switches the amp on. I tapped the pins as described in DIY:

3) Other Harman/Kardon equipped X5: After ejecting the connector you should now see 2 connectors side by side, a gray one and a black one. The pins are numbered from 1 to 13 on the gray connector and from 22 to 34 on the black one. The pictures 6 and 7 below show the 2 connectors. On this connector Pin #1 (-) and #2 (+) are for left rear woofer and pin #24 (-) and #25 (+) are for right rear woofer.

I am going to try hooking the rca's back into my bookshelf system and unplugging the battery. I think the noise may be caused be electronic going-ons while the car is off.

GLI is a good idea, I'm not sure if it will work since i am using high level inputs direct to amp. I may need to use my external line level converter if I have to use GLI.

[we350z]

Spoke with my audiophile buddy and MTX Customer support. They told me to use GLI as a last resort. He likened it to putting a straight jacket on a psycho path. He said, "fix your grounding problem".

He also told me that my choice in grounds (chassis, metal post of pass brake light) was among the worst possible. He said the best thing to do is to use a common ground for the HU. He also said to try the - batt terminal since it is easily accessable. He said if that doesn't work to run a wire from the HU to the amp ground terminal to normalize it. He said this should get rid of or significantly reduce the noise.

Which brings me to a question. Do the HU and the stock amp share a common ground? If so it would be easy to tap the ground on the amp wiring harness and wire it to the MTX ground instead of running a new wire from the HU (which isn't a big deal since I am replacing with 16:9 unit next week).

Using GLI also, for me wouldn't work since I am supplying a high level (speaker level) input to my amp. The amp itself converts the signal to low level. So if I want to use GLI, I have to use and external high to low lever converter then inline GLI to the amps low-level input. This adds more shit. I would prefer to avoid this scenario if possible.

[we350z]

I'm beginning to think this might not be the ground. If it is I hope running a ground wire from the headunit to the amp fixes it.

I switched my MTX amp ground to the - batt terminal. Still noise.

What's more is that i found while the noise still exists with the engine off it seems to be lessened, obviously there is no alternator wine either.

It is also relatively faint with the car off completely when i plug the inputs into the bookshelf stereo system. There is this strange low continuous ticking noise tho. That could be the NAV CD Player or anyhting i suppose.

I made another discovery. It looks like only the left channel is getting a signal, it also has the noise of course. I found that the bookshelf system is silent with only R plugged in and noisier with only L plugged in. Whats more is that the amp will only turn on when L is plugged in.

So what's the deal? Does the DIY have the wrong wires labeled for the harmon kardon right channel? Has anyone else had success doing this?

This sucks.

[ESP]

Its been a while (used to work as in istaller back in the mid 90s) since I have worked with any amplifiers that accept high level inputs but I have never been a big fan. I would personally use a line level converter, even WalMart sells a decent one made by Scosche.

That aside as suggested revisit your grounds. the Factory headunit ground should be fine, the amp needs to have a good ground, either directly to the battery or a good ground to bare metal (I use a ring terminal soldered to the neg cable, a 2 star-locking washers and either bolt or self tapping fastener to secure it to metal that has been scraped clean of paint.)

[dkl]

I wouldn't called your buddy an "audiophile" if he suggested that you run a single wire from the HU in the dash all the way back to the trunk where your amp reside. Doing so would most likely cause more noise than help as that wire would often acts as an antenna if it's ran close to anything that's noisy.

Your HU and amp DO share a common ground...it's called the CHASSIS. Make sure your amp is properly grounded to the chassis (bare metal contacts) with the shortest (no more than 6in.) and thickest ground wire you can find.

The easiest way for us to help you diagnose the problem is for you to provide pictures of your setup. I have no idea where you placed your amp, how you ran your wires, tapped your power/ground, etc...

[dkl]

Originally Posted by ESP

Its been a while (used to work as in istaller back in the mid 90s) since I have worked with any amplifiers that accept high level inputs but I have never been a big fan. I would personally use a line level converter, even WalMart sells a decent one made by Scosche.

That aside as suggested revisit your grounds. the Factory headunit ground should be fine, the amp needs to have a good ground, either directly to the battery or a good ground to bare metal (I use a ring terminal soldered to the neg cable, a 2 star-locking washers and either bolt or self tapping fastener to secure it to metal that has been scraped clean of paint.)

If the amp accept speaker level inputs, I would just use that instead of an additional LOC for obvious reasons. First, an LOC could introduce additional distortion. Second, the lower line level is more prone to picking up more noise.

Grounding the amp to the nearest bare metal is the best that you can do. Running a longer wire to the battery can introduce other ground loop issues depending on where he placed his amp.