Alternator whine with a twist

[Kyler]

I plug my Midland MTX-275 external speaker output into my aftermarket (Dual Elect XDM280BT) radio aux input plug.  I get a noticeable alternator whine.  I get the whine with the GMRS  turned on or off.  I tried a shielded 3.5mm audio cable and that didn't help.

I do not get the whine if I plug the car aux into my cell phone's 3.5mm output.  

I do not get the whine if I unplug the cable from the GMRS.

I tried putting an Install Bay IBNF30 Noise Filter on the GMRS radio but that didn't change anything; still had the whine.

Has anyone had the issue and does anyone else plug the GMRS into the car radio?

[SteveShannon]

20 minutes ago, Kyler said:

I plug my Midland MTX-275 external speaker output into my aftermarket (Dual Elect XDM280BT) radio aux input plug.  I get a noticeable alternator whine.  I get the whine with the GMRS  turned on or off.  I tried a shielded 3.5mm audio cable and that didn't help.

I do not get the whine if I plug the car aux into my cell phone's 3.5mm output.  

I do not get the whine if I unplug the cable from the GMRS.

I tried putting an Install Bay IBNF30 Noise Filter on the GMRS radio but that didn't change anything; still had the whine.

Has anyone had the issue and does anyone else plug the GMRS into the car radio?

I do not connect my two-way radio to the car radio. 
I am curious if you hear the whine when the cable is unplugged from your car radio input. 
What is the impedance at both ends of the connection?

Typically speaker level outputs should not be connected to line level inputs. Line outputs or earphone level outputs are better matched. 

[Kyler]

16 minutes ago, Sshannon said:

I do not connect my two-way radio to the car radio. 
I am curious if you hear the whine when the cable is unplugged from your car radio input. 
What is the impedance at both ends of the connection?

Typically speaker level outputs should not be connected to line level inputs. Line outputs or earphone level outputs are better matched. 

No whine when the cable is unplugged from the car.

No idea what the impedance is nor how to measure that.

I was assuming since my phone output worked that the GMRS would work the same way.

[SteveShannon]

2 hours ago, Kyler said:

No whine when the cable is unplugged from the car.

No idea what the impedance is nor how to measure that.

I was assuming since my phone output worked that the GMRS would work the same way.

Your phone output goes to earphones or an amplified speaker, devices which expect low levels, not directly to a speaker.
A speaker output typically drives a 4-16 ohm load (the speaker).

If your radio has a headphone output, that would match your car radio input better. 

[WRQC527]

4 hours ago, Kyler said:

I plug my Midland MTX-275 external speaker output into my aftermarket (Dual Elect XDM280BT) radio aux input plug.  I get a noticeable alternator whine.  I get the whine with the GMRS  turned on or off.  I tried a shielded 3.5mm audio cable and that didn't help.

I do not get the whine if I plug the car aux into my cell phone's 3.5mm output.  

I do not get the whine if I unplug the cable from the GMRS.

I tried putting an Install Bay IBNF30 Noise Filter on the GMRS radio but that didn't change anything; still had the whine.

Has anyone had the issue and does anyone else plug the GMRS into the car radio?

I'll preface this by saying I'm no expert. But I have dealt with alternator whine on my radios. The approach that fixed it for me is a homebrew inline filter between the battery and the radio. Here's the link to the filter I built. It looks very similar to the IBNF30 you bought.

https://www.sanantoniohams.org/Tips/whine.htm

But, since you say you tried the filter and it didn't work, I would suspect a ground loop. This can happen when two devices are grounded to different places of the vehicle. And in your case, connecting the Midland to the car stereo with a cable introduces yet another ground path. Without knowing what your wiring setup is, I'm guessing. Perhaps you could try to run the Midland off a battery that is completely isolated from the car's electrical system and see if that has an effect. If so, grounding the Midland to the same place the car radio is grounded to might help. Additionally, because the cable connecting the Midland to the car radio introduces a direct ground connection between them, an audio isolation transformer might help. Something like this. It completely breaks the electrical connection but it passes audio.

https://www.connection.com/product/c2g-stereo-audio-isolation-transformer-3.5mm-m-f-black-4in/40000/13364621

Bottom line, do some research on ground loops in car audio systems. If I were a betting man I would bet this is the issue.

[Kyler]

13 hours ago, WRQC527 said:

Additionally, because the cable connecting the Midland to the car radio introduces a direct ground connection between them, an audio isolation transformer might help. Something like this. It completely breaks the electrical connection but it passes audio.

https://www.connection.com/product/c2g-stereo-audio-isolation-transformer-3.5mm-m-f-black-4in/40000/13364621

Bottom line, do some research on ground loops in car audio systems. If I were a betting man I would bet this is the issue.

Thanks for the suggestions.  I've read up on ground loops and decided to try the audio isolation transformer first.  

Thanks!

[SteveShannon]

Here’s a short thread from last year about connecting a speaker output to a car audio system, similar to what you’re doing.  In his first post, the OP includes a link to a “speaker to line level” adapter to handle the concern I raised.  That probably offers a degree of isolation as well.

Here’s the converter: https://www.amazon.com/dp/B07VKFSLKN/

Here’s the thread: 

 

[Kyler]

17 minutes ago, Sshannon said:

Here’s a short thread from last year about connecting a speaker output to a car audio system, similar to what you’re doing.  In his first post, the OP includes a link to a “speaker to line level” adapter to handle the concern I raised.  That probably offers a degree of isolation as well.

Here’s the converter: https://www.amazon.com/dp/B07VKFSLKN/

Here’s the thread: 

 

if the audio isolation transformer I ordered doesn't work, I'll try this.  Thanks!

[Kyler]

I installed a "BESIGN Ground Loop Noise Isolator for Car Audio/Home Stereo System with 3.5mm Audio Cable" that I got from Amazon.  In a quick test parked in the driveway there was no whine even with the car radio at its highest volume with the GMRS on.  

 

Here's a big thanks to everyone who responded!  I'm very grateful.  I've spent months trying research and fix this on my one.  WRQC527 nailed it on the first go.  I should have started here.

[K7lon]

When I suffer the wining noise. These are the things I did to make it go away. Clean the battery post/ cables, clean and tighten ground wires, and clean the alternator stator/ replace the brushs. It seem to work on my late 80's through 90's vechicles. Just a thought

Good luck 

WRJA397