still got radio noise

[corelokt]

I put all the military noise filters into my inside power feeds, and grounded the firewall real well, but still have alternator "feedback", a high pitched noise, that gets louder as the engine revs higher, feeding through my stereo and coming out the speakers, how do I cure this?
p.s. quite the run on sentence, huh?

 

[WillWagner]

Try these.
http://www.radioshack.com/product/index.jsp?productId=2103222

 

[ida34]

You might have an alt ready to go bad. Did you have a suppressor on the input line to your radio?

 

[ems4ty]

Loop your power wire to your radio a few times through a Ferrite Choke or two. If that doesn't help, you can get a noise supressor from most car audio places, those help filter out the noise. Otherwise, time to pony up and take a good look at maybe rebuilding the alternator.

-Tyler

 

[n1bnc]

Sometimes a diode goes sour in the regulator in the alternator. When that happens you get a very ripply sort of AC coming through instead of clean DC. Easiest to check this with an oscilloscope, but not many folks here have one handy. If you have another alternator hanging around, try swapping it in.

 

[corelokt]

What's a ferrite choke?

 

[ems4ty]

See the radio shack link in the 2nd post above.

A Ferrite Choke is an RFI (Radio Frequency Interferance) reducer. I good applications it can eliminate noise heard in audio devices. Other times it'll at least reduce the noise and sometimes won't do anything at all. They are fairly cheap. Lots of devices use a Ferrite Choke on the power cords. Check your electronics at home, TV, DVD Player, Sound System, Audio Cables, if you see a buldge in the cord, it's probably a Ferrite Choke.

-Tyler

 

[kc5mzd]

In addition to the choke you can also add a capacitor across the power lead to the radio. A choke makes a kind of magnetic field that blocks AC, a capacitor (also from radio shack) absorbs AC. If you check the alternator voltage with a digital voltmeter and the voltage jumps around it could be a bad alternator diode. You can also measure the voltage from the frame to the engine block, from the body to the engine block, and from the body to the frame. Any voltage would suggest a bad ground. You can also check for voltage from the battery - to frame, engine, or body a voltage here might also indicate a bad ground. You can also try running the power wire directly to the battery, if the noise goes away it would suggest a bad ground. Sometimes cheaply made radios can be overly susceptible to interference. You might try a different model / brand of radio.