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Radio noise when turning car off

R

rmarks

Member
I had my Factory AM/8-track converted to AM/FM 8-track and every time I turn the car off the radio makes a weird noise that's hard to describe. By a fluke I turned the ignition off with the heater control blower switch in the on position and presto no more noise when shutting the car off. Any ideas on why the noise and why it would go away with the blower on?

Kind of annoying and I'd like to eliminate the noise without having to leave the blower switch on all the time. Perplexing.
 
I worked at a stereo store for a number of years. I encountered this once and our radio repair guy explained to me why it happened. I can't promise it is correct but it is a start.

A stereo has capacitors in the amplifier section. These store power for the internal amplifier to use when there is need to reproduce louder or peak sounds. Somewhat like an internal battery which is only charged when the radio is on.

When the radio is turned off, these capacitors discharge. They cause the speakers to make a strange noise until the power is depleated. If the heater is on the heater pulls the power from the capacitors through the circuit and there is no noise made by the speakers.

I've seen some radios come with a noise suppresor box inline on the power and ground wire going into the radio. My understanding was that these were added to avoid this issue.
 
"67TXStang" said:
I've seen some radios come with a noise suppresor box inline on the power and ground wire going into the radio. My understanding was that these were added to avoid this issue.
Click to expand...

Any idea what they look like or where I could get one for a radio like mine. Checked Radio Shack and Best Buy with no luck.
 
Try giving a shop that sells and installs stereos. They normally have all the parts and pieces for doing custom installs.
 
The example post show some of the type noise suppressors used. It would wire inline with the power and ground going to the radio. While the link shows some example noise suppressors, I would NOT buy anything made by Pryamid.

Before you buy anything, I would suggest you make sure your ground wire to the radio is connected well. Make sure the negative terminal from the battery is connected well to a chassis ground. Finally, I would run a separate ground to the chassis of the radio.

I've used a variety of noise suppressors and it is hit or miss on if they fix the problem. I would second the idea of going to a local car audio shop. They would likely have the part (and may allow you to return it if it does not work for you). Additionally, they would be able to actually hear the problem and give you their opinion.

Just to confirm... you are just using the radio right? There is no amplifer or anything.
 
"67TXStang" said:
Just to confirm... you are just using the radio right? There is no amplifer or anything.
Click to expand...

Yes, just the radio with door speakers and a dual cone speaker in the dash. And, I don't have RCA-type connectors those noise suppressors have.
 
I need to buy one of the noise suppressors as well. When I completed my rewiring under the dash, I hooked the radio ground wire up in a different spot. I get noise now through my radio based on the RPM's the motor is turning.
 
"RustyRed" said:
I need to buy one of the noise suppressors as well. When I completed my rewiring under the dash, I hooked the radio ground wire up in a different spot. I get noise now through my radio based on the RPM's the motor is turning.
Click to expand...

What you have is called a ground loop. It's a very small current caused by grounds having different resistances to 'true' ground. The resistance invovled is not measurable with a normal ohmeter. This is especially prevalent with multicomponent systems (head unit / amps / sat radios) tied together. Power filters won't work, since very few (if any) do anything with the ground noise.

Work on your grounds - use a large ga wire, make sure it is tight, use star washers, etc. In extreme cases, bring all the grounds back to one point, perhaps even the point where the alt grounds.

I put a sat radio in my M5, and couldn't get rid of the low level whine until I used 12 ga wire to bond the grounds together - all grounds brought back to one point, soldered, and star washered to the main ground point for the car.
 
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