link2009

Okay, I've been trying everything for the past 36 hours (And no, this is not an exaggeration).

I started getting a low-tone buzz (~50Hz) from my subwoofer and front components, which are both amped.

My equipment is as follows:

• Honda Civic 2009 DX-G (Non-premium system)
• MB Quart FX1.600 (50 amps)
• Boston Acoustics GT2125 (40 amps)
• Polk Audio DB6501
• Polk Audio db1040
• Kenwood KDC-MP745U
• Power/Ground distribution block, power is fused
• 4-Gauge power and ground split to (2) 8-Gauge power/ground
• 100 amp fuse 4" from battery

I determined the problem is with the headunit since once I unplug the RCAs, the noise completely stops, with both amplifiers.

I made sure the RCAs were clear of any interference from any power / signal cables, while moving the RCAs the noise did not stop.

I had a shop install the headunit for me and they used the stock ground location.

I spliced the ground wire (black wire) and used a marette to ground it to a point on the chassis. I've tried grounding the amplifier and the headunit to the same point. That is, the back where there were 5 other wires grounded, that still kept the humming. The seat belt bolt on the power side, that kept the noise going. I drilled my own hole into the rear deck (under the window) and the noise STILL persisted.

I am TOTALLY out of ideas guys. The antenna lead is disconnected on the headunit (Yes, it grounded through it once, that's how I know). I also tried modifying the sensitivity of the amplifiers but only if I turn it leftmost does the noise actually 'get less intense'.

Please, if somebody can suggest anything, I would appreciate it. I have a ground loop isolator that eliminated hissing problem (alternator whine) before I purchased my subwoofer but now does absolutely nothing.

I've read every guide, followed every tutorial, I'm lost. The only thing I can think of is that the ground wires are too long. (The amp ground is 6' and the HU ground is around 15').

Sinemeup

Try putting a noise filter on both the Constant (YEL) and the Acc (RED) wires of your headunit... you can mimic using two by running both RED/YEL wires through one noise filter, if the noise goes away then go out and buy another filter

kevmurray

Replace the RCA with a known good one and remove the isolator (temporarily). Grounding the head unit to the same physical location as the amps is good but the audio ground in your amps is not likely the system ground. A "floating ground" is often used to avoid things like alternator whine. I suspect you have lost the audio ground reference.
I think if you take your system down to a basic level with a known good RCA cable we will be able to guide you through the steps to find the problem. A few questions which can help:

Does the Honda head unit have RCA ouputs?
What happens if you have only one amp at a time connected to the RCA's?
What happens when the isolator is removed and you listen with the engine off?

link2009

Hmm, I don't have a noise filter and I would have to splice the constant and ACC wires, they are so well taped I can only cut them. And putting them back into the harness without the HU trim removed will be a PITA.

I did remove the noise isolator and changed the RCA cables. Same problem unfortunately.

The head unit I am using is the Kenwood KDC-MP745u, aftermarket HU.
The same problem happens with either RCA cables and either amp.
If I only turn the key once (1st position), there is no noise. The moment I put it into 2nd (auxillary), the humming starts. If I turn on the headlights, the humming dims. If I turn on the high beams, the humming is completely off.

kevmurray

Do you have an ipod or some other portable source you can try? It's weird that the headlights have anything to do with it but maybe they have a chopper circuit which is bypassed when the high beams are on. An external source would be immune to it.

Anyone know if the Kenwoods use the pico-fuses on the RCA grounds like the pioneers?

link2009

Do you mean source through the head unit or through seperate RCAs? I hooked up my phone to the amplifiers and the noise stopped.

I think I know what you're talking about in regards to the Pioneer HUs. I saw an image where someone recommended grounding the RCAs shields to the chassis of the HU but I understand that is ONLY for pioneer units.

MR2NR

iTrader: (66)

It can be done on any head unit but to me it sounds like you need to borrow a head unit and eliminate another suspect.

kevmurray

Separate RCA's and the phone is perfect. That means it's definitely coming from the head unit.

Nope like MR2NR said you can try it on yours. Some head units use a fuse inline with the RCA grounds to protect the head from an amp grounding through the RCA's. You can restore the connection with a wire temporarily to test it. If it cures your problem you should consider how the fuse in the head unit popped.

link2009

Funny thing, the stock speakers amplified through the HU work fine and have no noise issues.

Interesting you mention that fuse issue. Are you saying the 10A fuse on my HU could have popped? Or are you referring to a fuse INSIDE the HU that protects it from having an amp grounding through the RCAs?

Wow...this means that when I removed and inserted the RCAs while the amps and HU were running, I may have blown that fuse? The amp ground is < 6ft and I assumed it would only try to ground through there...

So do I just wire the HU's RCAs to the chassis of the HU and see if the noise stops?

EDIT: I found this http://www.mazdas247.com/forum/showthread.php?123683108-Please-help-me-with-the-ground-loop-from-hell.&

Different HU but the problem is SO similar... so if that fuse blew, I need to service the HU? I can't diagnose if it did or not?

audio1der

Try it:
http://www.ecoustics.com/electronics/forum/car-audio/644177.html

Short of that, have you tried listening without the HU installed in the dash?