Aftermarket Head Unit in 99 LC - Engine Noise in Speakers

[suprarx7nut]

Hey all. I know this topic has been discussed, but I was unable to find many folks who came back to complete the story and say what actually worked - hence this thread.

I have the common "engine noise" or "Alternator whine" or "hum" or "hiss" that happens in the speakers when using the factory amp with aftermarket head units.

I am using the "Best" brand harness adapter which has RCAs for the aftermarket head unit to tie into the factory amp. I have not touched anything with the factory amp or speakers. Everything I'm using (aside from the harness adapter) is brand name - Alpine, Rockford, Kicker, Pioneer. Harness adapter below.

http://www.amazon.com/gp/product/B0088TNXLI?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00

Many others have faced this problem, but few seem to have responded after trying a few things. The threads just die off with someone saying, "Ok, I'll try that." and never reach final verification of the solution.

So, what have people tried? What has worked (without replacing the factory amp)? What doesn't work?

Anyone tried this sort of thing in the 12v line(s) for the head unit?

http://www.amazon.com/Pyramid-NS12-...p/B0007V5X4U/ref=cm_cr_pr_product_top?ie=UTF8

I hear ground loop isolators can eliminate noise well, but that they muddy the sound and decrease sound quality. Has anyone used these isolators and still had good sound quality?

Thanks for all replies. I'm putting together a YouTube video of my install and would love to include some good info on this noise issue that seems to be universal to LCs using the factory amp.

 

[Overland Tailor]

Install a ferrite choke on the units power wire. The power wire for the radio unfortunately connects inline with other 12V sources that pick up the "whine" which is RF interference.

When we install HAM radios and CB's we go direct to battery to reduce this, but sometimes a choke is required.

Good luck -

J

 

[SALTY METHODS]

I had the same wine after I installed my aftermarket head unit and aftermarket amp. My car stereo installer friend told me to replace the AV cable that runs from the head unit to the amp with a premium one. I was a little skeptical but I bought it, installed it and it fixed the wine problem. He explained that cheaper AV cables allow too much signal leakage and for some reason it comes through to the speakers.

 

[Colorado80]

Without getting into a long winded discussion; install a "reference ground" between the headunit and the factory amp. For more information on this please watch this video:

 

[suprarx7nut]

Install a ferrite choke on the units power wire. The power wire for the radio unfortunately connects inline with other 12V sources that pick up the "whine" which is RF interference.

When we install HAM radios and CB's we go direct to battery to reduce this, but sometimes a choke is required.

Good luck -

J

Interesting. I'll try to run a length of wire straight to the battery to test this out.

I had the same wine after I installed my aftermarket head unit and aftermarket amp. My car stereo installer friend told me to replace the AV cable that runs from the head unit to the amp with a premium one. I was a little skeptical but I bought it, installed it and it fixed the wine problem. He explained that cheaper AV cables allow too much signal leakage and for some reason it comes through to the speakers.

Does this apply to the stock wiring? I'm using the factory amp and therefore the factory wiring... which worked perfectly with the stock head unit.

I think your reply is aimed at aftermarket amps, yes?

Without getting into a long winded discussion; install a "reference ground" between the headunit and the factory amp. For more information on this please watch this video:

I thought this might solve it so I put in a ground eyelet on the frame surrounding the radio and attached the ground from the stereo and the ground wire from the car's factory harness. It made no difference at all. It's still installed that way. Is the steel frame surrounding the center dash a poor ground on a 100 series? I'll go verify with a DMM, but I figured that would be a good solid ground.

 

[re_guderian]

OP - Do you have the factory electrical wiring diagram? If you're using the stock harness, both the power and ground come through a shielded harness from the stock amp to the HU. Do you have any other accessories coming out of the new HU besides the speakers (A/V our, DVD, etc?)

I ran an extra ground from the HU with no difference, it was already grounded well. Ground loop isolator solved my particular problem. As to sound quality, it sounds way better than the crappy whine. Though your issue may be different...

 

[12guns]

I had the same issues with engine noise. It completely went away when I bypasses the stock amp and ran the speakers direct from the head unit. Much better sound too.

 

[SanDiegoCruiser]

I spent a ton of effort trying to fix this. Nothing worked. I used RedRob's instructions on how to bypass the factory amp. My sub's are only powered by the factory amp. All of the other speakers use the head unit's internal amp. Works great!

 

[suprarx7nut]

OP - Do you have the factory electrical wiring diagram? If you're using the stock harness, both the power and ground come through a shielded harness from the stock amp to the HU. Do you have any other accessories coming out of the new HU besides the speakers (A/V our, DVD, etc?)

I ran an extra ground from the HU with no difference, it was already grounded well. Ground loop isolator solved my particular problem. As to sound quality, it sounds way better than the crappy whine. Though your issue may be different...

I haven't got a wiring book for my specific year, no. I have one that I got online, but it's a newer model year. Not sure what wires are the same. My issues sounds like yours. The ground loop isolator is a possible solution here. It may be the only thing that cures this in these cars.

I had the same issues with engine noise. It completely went away when I bypasses the stock amp and ran the speakers direct from the head unit. Much better sound too.

That's a very good suggestion. I'd read about that, but wasn't really considering it. So the stock speakers sound fine running on just regular head unit power?

I spent a ton of effort trying to fix this. Nothing worked. I used RedRob's instructions on how to bypass the factory amp. My sub's are only powered by the factory amp. All of the other speakers use the head unit's internal amp. Works great!

Thanks for the reply. Sounds like bypassing may be a viable solution. I was thinking it would sound horribly under-powered for some reason.

 

[suprarx7nut]

Well, I learned a few things tonight playing with a multimeter in the car.

1. The noise was greatly reduced using power straight from the battery. It seems the power in the factory harness coming from the factory amp is dirty like main st hook... never mind. It's dirty. That seems like one problem.

2. The RCA shield lines in the factory harness are NOT the same as chassis ground. The factory amp's leads have very high resistance to ground (k-MOhm range). With the key turned to ACC or ON the RCA shields have a potential of 0.1V-0.3V. This is a big problem for an aftermarket head unit that uses ground for the RCA shielding. With the RCA cables disconnected, the Head unit RCA shields are grounded. Testing the disconnected RCA shields in the patch harness shows high resistance to ground. Plugging the RCA leads into the head unit (still turned off) results in a slightly lower, still relatively high resistance reading. It looks like the factory system uses it's own separate ground loop making interaction with an aftermarket head unit difficult.

3. Using the factory amp ground loop as the overall ground for the head unit doesn't work. I removed any grounds to the aftermarket head unit by pulling terminals from the connectors and combined them all at the factory amp RCA shielding wire (theoretically the ground for that circuit). The result was a very weak 2-3 volts. No dice there.

4. The steel frame in the center of the dash is NOT grounded. It's on some other ground loop or something. This is the first time I've seen that, having worked on my fair share of cars and sound systems. I usually test them with a DMM, but skipped this time. So much for that ground point. I may need to run a wire to the firewall in a foot well or something to find a good ground. Perhaps providing a good true ground outside the factory wiring will help. This being said, when tested, the factory ground in the harness shows it's a true ground. 0.2 Ohms.

Knowing that the factory amp provides an active non-ground signal to the RCA shielding, do I stand any chance of eliminating some level of hiss? That seems like a pretty fundamental, permanent problem with the factory amp and aftermarket head units, even if power and ground are sorted out for the head unit.

 

[suprarx7nut]

Update on this issue.

I resolved it completely by bypassing the factory amp. There is no buzz, hum or whine at all now. Not only that, but the speaker levels match much more closely with my aftermarket sub. With the factory amp, the door speakers were waaaaaay louder than the sub. I had to turn the sub gains and "bass boosts" up all the way to get it close to matching volumes with the door speakers. After bypassing, the speakers all match pretty well with no extra gain or boost.

The factory amp (at least in my case, and I assume others) does NOT use chassis ground as the shielding for the RCA lines. Aftermarket head units do. This is a serious problem and was the cause of my whine.

I'm sure you can use a ground loop isolator to get around the problem, but those degrade clarity unless you get a very high-end one. They're a band-aid for cancer. It may not make a huge difference in the factory speakers, but it would likely be noticeable with any decent aftermarket speakers. Those isolators attempt to use a one-to-one transformer to take the signal and transfer it over to another wire. It works fine for basic signals, but that's not a good way to treat your analog audio signal.

I'll be putting together a video showing what I did and all the things that didn't work. I feel like this is a really common problem that's not very well documented with a definitive solution easily found by folks like myself. Hopefully I can put together something to help others facing the same problem!

 

[suprarx7nut]

Youtube video on Amp Bypass:



More to follow on the stereo/sub/amp install.