I completely re-did the audio on my '97 Z3, replacing everything but the factory wiring. Problem is, I've got a very slight rpm-dependent whistle coming thru the system. I've got two power amps in the trunk with a common ground (the battery ground post), and the head unit grounds to wherever the factory HU grounded to. My thought was that I had a ground loop occurring due to the amps and the HU being grounded to different points. So, I went to Radio shack and picked up three (front, rear, and sub...the preamp outs ) ground loop isolators and connected them. Still whistles.
I'm wondering this... I connected the isolators between the HU pre outs and the wires leading back to the amps. Is that length of wire now picking up a loop again? In other words, should I have installed the ground loop isolators between the wires coming from the HU and the amp inputs, back at the amp end? Does it make a difference?
Here's what I recommend.
1. First, recheck all the connections on the amp, particularly the grounds, and make sure they are tight. I've seen a poor ground connection on the amp cause noise.
2. With the right RCA to 3/8" adapter you should be able to connect your iPod/iPhone/Android/whatever directly to the amp input in the trunk. You can vary the music player level out and vary the amp input gain as necessary to get to a comfortable listening level. Disconnect all the other inputs from the head unit. Then run the engine and/or drive around to see if you can still hear the whine.
3. If step 2 eliminated the noise then I'd try your "move the isolators" idea.
4. Move the amp grounds from the battery to the factory amp ground point. I think the head unit is grounded at the some point . . . I've never verified this but it would make sense for ground loop control.
5. Try removing the antenna connection from the head unit and see if that makes a difference.
6. If you've made it all the way to this point then my bet is you'll have to add some additional power line filtering at the head unit. I've had the best luck in this case where I filtered BOTH the switched and unswitched power.
If step 6 turns out to the issue (and frankly my money is on that one) then you many be able to remove those silly ground loop isolators. Those things have tiny little audio transformers in them and can impact sound quality.
What brand head unit do you have and what brand amps? The better amps will have differential inputs that are completely isolated from ground so a ground loop isolator does no good in that case.
Cheers.
Keith
All my advice comes with a 10x Golden Money Back Guarantee! If you're not completely satisfied, I'll gladly refund 10 times what you paid me for the advice!
'03 330i Zhp - My Car
'04 330i - Wife
'98 328i - Son
I didn't really read kgvicker's post, but all I had to do to solve my alternator wine was use two separate ground points for each amp. I guess too much wattage to one ground point causes alternator wine. Might want to add that to your list.
First, get those ground loop isolaters out of your system...that is amateur hack stuff.
Change your ground point first. Use the bolt that connects the battery to the chassis, not the battery terminal itself, see if that changes things...then, do as kgvickers suggested and use a separate source to test for noise so you can get down to what is actually causing the noise.
Also, if you don't mind, list all the equipment and what RCA cables you used. There may be issues elsewhere too, see what the status is on these ideas first.
You just got lucky, "star" grounding is correct, all components need to see the same ground point. I have personally used a single (HUGE) ground point for 15KW of power, it is not a wattage thing.
Definitely move the grounds to the factory audio ground in the trunk. The battery ground is notoriously noisy.
Just to clarify...the ground I'm using for the amps is NOT the negative post on the battery, but rather the bolt welded to the floor that the battery grounds to. I'd be happy to try the factory audio ground...where is it on a '97 roady?
Last edited by johnnyo55; 11-29-2013 at 06:14 AM.
I don't know about your Z3 but on all my BMWs the ground point is located in the trunk near the amp.
Look for a group of brown wires all terminated into an assembly which will be physically bolted to the car body.
Keith
All my advice comes with a 10x Golden Money Back Guarantee! If you're not completely satisfied, I'll gladly refund 10 times what you paid me for the advice!
'03 330i Zhp - My Car
'04 330i - Wife
'98 328i - Son
No, don't bother, the body ground point is the most stable ground anywhere in your car, period. If both of your amps are grounded on that bolt, no worries, its good (unless you used crap wire or have lame connections) but it isn't your amps or your ground, it is a completely different issue...its your deck.
In fact, if I were you I would just do a quick test-wire of any other deck you can find, I would bet the noise goes away. Borrow one from a buddy or buy one from WalMart (Pioneer means no re-wiring!) just for testing purposes. It needs to be something fully installed, an iPod does not connect to the chassis electrical so it is not a viable test in this case. Just grab any old deck with RCAs and test for noise...I would just about guarantee its gone.
Please don't take this as some sort of anti-Pioneer thing; it isn't. In fact, I really like Pioneer but they do have some common issues. The biggest issue that have is a poor choice in capacitor quality, it allows noise like you are having to slip through.
If you hit "track up" do you hear a weird little "screedling" noise between tracks? If so, the deck is bad, just stop there and replace it. Swap the deck, you will know in minutes.
GL!
Luke
I don't know how the impression got around that my deck was a Pioneer, but it's not. Here's what I'm running: The HU is an Alpine CDE-HD148BT, which has preamp outs. These are what I'm using, and what I've connected the ground loop isolators to. I have two amps, an Alpine HTP-445U (45W x 4) to feed the "regular" speakers (Focal 5.25" coaxes in the kickpanels and Focal 4" coaxes behind the seats) and an Alpine MRP-350 (250w x1) to feed a Pyramid 6.5" sub behind the seats. I've managed to reutilize the factory wiring for all but the lines from the amp to the sub. The "whistle" I'm complaining about is very subtle; can't really hear it when the top is down. Additionally, it seems to vary in intensity for no particular reason...louder one day than the next. The intensity also, of course, increases with engine rpm.
Seems someone said Pioneer....no, your deck is fine, but you bought a miserable pile of crap for a mid-high amp. The KTP 445U is one of the noisiest piles of misbegotten garbage I have ever had the displeasure of installing. 78DBA S/N ratio? Hell no, thats like FM radio noise levels! Most $75 Taiwan amps do better, it's that bad. I only know of one other amp that came with ground loop isolaters (I have installed roughly 30 KTP445U BTW) and that clearly shows that Alpine know their product is a known "noise bomb". If you call 1-800-ALPINE1 and talk to their techs, they will tell you to wire it "high-level", as in NOT using RCAs...because they can't control the noise in their own amplifier either.
Pitch that turd and get a normal 4 channel, all your noise issues will be gone AND you will have better clarity.
GL
Luke
I was asking if it was Pioneer due to the common pico fuse issue. Apologies for the confusion caused.
My first trouble shoot would be to start disconnecting amps to determine where the whine is coming through
Last edited by rogan; 12-02-2013 at 09:41 PM.
Mutual Admiration SocietyFounding member
Thanks for the info, M20E34. I appreciate your opinion regarding the 445; while it might not have been my first choice, it WAS free, and I figured that it was a current model from Alpine, so it couldn't be a complete piece of junk. I'm a little confused, though...does the 445 come with ground loop isolators integral to the unit? Also, what exactly does wiring it "high-level" mean? Does that mean wiring it to the preamp outs rather than the HU amp output, or does it refer to the physical connection from the HU to the 445? I'll probably end up replacing the 445 eventually, but finances preclude that right now. Do you have a recommendation for a replacement? TIA for any further info...
Those 2 ground loop isolaters you got at Radio Shack? Yes, the KTP 445U comes with those when new...shocking, huh? And yes, Alpine expects you to run it from the speaker outputs, like a booster amp from 1978. As far as a replacement, just pick a 4 channel you like the looks of, or better yet consider replacing both of your amplifiers with a 5 channel so you can get a little more power on bass. Figure it like this: there are plenty of nice 4 channel amps for $100 to $200, but 5 channel amps are typically $150 to $200, so it may be a good move.
Otherwise, consider finding the 4 channel that matches your bass amp, MRV-F300 maybe? Any Alpine amp that is MRV is a solid choice and commonly are sold on CL for $50 or so used.
If I can help, feel free to PM me.
Luke
http://www.installdr.com/TechDocs/999502.pdf
this will solve your problem.
Last edited by oiphy; 12-19-2013 at 03:45 PM. Reason: more info
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