How to avoid engine feedback thru PSR500 speaker when connected to car audio input

[dizwiz]

Hello.

this is probably really basic question for the electronics gurus

Whenever i connect the dc 12v adapter to my PSR500, and set on scan....there is a terrible high pitched hum coming thru it when my car engine is running (1993 chevrolet).

i can still hear loud and clear the scanner traffic, but there is still this humm. Its awful.

if i run it on batteries no problems.

(On a sidenote: i love the way i have spliced into my audio. Basically the scanner traffic broadcasts on top of the radio or whatever im listening too.)

 

[tvengr]

Does the pitch of the hum vary with engine speed?

 

[cpetraglia]

Look around for an auto stereo power noise eliminator. Wire it straight to the battery before your 12v adapter. They are cheap and everyone sells them.

 

[prcguy]

This sounds like a ground loop where the power adapter ground and stereo ground are at different potentials and its trying to equalize that through the shield of the audio cable between devices and the noise is being induced into the audio cable. A power line filter might help, might not. Breaking the shield of the audio cable and bridging that with a few uf of capacitance might help or using an audio isolation transformer in the audio cable should fix it.

Do you also have an external antenna feeding the scanner that is grounded to the vehicle body? There is another potential ground loop source.

 

[buddrousa]

Or the Alternator is starting to have problems. You can take an oscilloscope and put on the battery leads while the care is running you will see a AC ripple on the voltage.

 

[tvengr]

If the pitch varies with the engine speed, it will be alternator whine. If not, it could be the computer. I agree to disconnect it from the car radio to see if that clears the problem. If that fixes it, use a ground loop isolator. If not, try a noise filter in your 12v lead.

 

[doctordialtone]

really basic question for the electronics gurus

THIS WILL WORK FOR YOU
Ground Loop Isolator

 

[dizwiz]

Does the pitch of the hum vary with engine speed?

Yes i believe it does.

alternator is tight. Ive got 14+ volts.

car is not a zonk mobile.

the antenna is a BNC connector with an 800 mhz ducky antenna sticking up from the roof gutter

 

[tvengr]

What happens if you use a scanner mounted antenna instead of the gutter mount?

 

[buddrousa]

Yes i believe it does.

alternator is tight. Ive got 14+ volts.

car is not a zonk mobile.

the antenna is a BNC connector with an 800 mhz ducky antenna sticking up from the roof gutter

Just because you have a Alternator Whine does not make your car a ZONK MOBILE I have installed Police Radios in new Police Cars that had the whine the Alternator was replaced or a Power Filter and fixed the problem.

 

[byndhlptom]

"car is not a zonk mobile. "

OK, I give up.... What is a zonk mobile?

$.02

 

[doctordialtone]

What is a zonk mobile?

 

[buddrousa]

Zonk Mobile = Rolling Pile of Junk
We also got 2 new Custom Built Fire Trucks built just alike at the same time 1 needed a filter 1 did not.

 

[prodigyonline]

Or the Alternator is starting to have problems. You can take an oscilloscope and put on the battery leads while the care is running you will see a AC ripple on the voltage.

Ground loop noise has nothing to do with the health of an alternator as far as I know.... I've worked with many alternators and audio systems, I'm sure anything is possible but i've never seen it

THIS WILL WORK FOR YOU
Ground Loop Isolator

This would work, if the scanner is plugged in via AUX. But this guy has spliced his scanner audio directly into his radio signal wires, if I am reading the first post correctly.....

Dizwiz, can you elaborate on how you "spliced into your audio" ?

 

[a417]

Ground loop noise has nothing to do with the health of an alternator as far as I know.... I've worked with many alternators and audio systems, I'm sure anything is possible but i've never seen it

You've conflated two posts into one. @tvengr referred to a ground loop, and @buddrousa was talking about AC ripple in an alternator. They were separate and distinct posts referring to separate and distinct issues.

As for your second part "by splicing it directly into his radio signal wires" as you put it, the sky is the limit...let's see.

 

[dizwiz]

THIS WILL WORK FOR YOU
Ground Loop Isolator

ok i bought this, it was about $6 but took 6 weeks to arrive....

It fixed the whine/humm coming thru the speakers.

however it reduced the amplified volume level so much that there is now no advantage to having it come thru the car’s audio vs. just having it come out thru the scanners external speaker which never had a humm even with it plugged in/engine on..

 

[KK4JUG]

I think the ground loop isolator is nothing but a choke. I have a bag of about 15 in various sizes that cost $5.00.

 

[doctordialtone]

It fixed the whine/humm coming thru the speakers.

Great news!

Happy it got rid of the noise you mentioned.

 

[buddrousa]

I use them alot on line level output with no problems.

 

[Ubbe]

I think the ground loop isolator is nothing but a choke. I have a bag of about 15 in various sizes that cost $5.00.

It's a high impedance galvanic isolated transformer, usually two of them to handle stereo signals. It is not suited for low impedance loudspeakers. It helps with most noise problems from humm and generator whining.

/Ubbe