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AC EMI filter in my car ? Answered

Is it possible to use an AC EMI filter in my car. have a lot of interference coming through my speakers.
was given a new EMI filter, thought I'd try used it.



Best Answer 4 years ago

Have a look here to a see a hummy speaker treatment .

Those EMI filters contain Bauln ferromagnetic bucking coils that only work on AC lines to cancel common mode noise.

Except for a few small capacitors this filter is quite useless in a 12VDC car.

Better you should attend to the alternator output and also verify the ignition resistance wiring is correct for best noise reduction.

See the kind of circuitry you will find inside an AC EMI filter like your picture.

Electro Magnetic Interference does not cover RFI Radiated Frequency Interference that is found in your car.

Does the interference in your speakers still occur when your engine is OFF??

If Yeswhen off look at the amplifiers as the noise source..

If No ... when running ... Try putting the amplifiers on a separate battery, just to find out if the noise is radiated ? or only conducted ?

Let us know !

bauln circuit.PNG

Hi. thanks for reply.
There is no noise when the car engine is off.
I will try power the amplifier off a separate battery.

BTW , I have ordered a 12 volt car noise suppressor/ filter. Thought that might help.

" Blue Input Red Output Wiring Power Supply Noise Filter for Car Truck "



I installed the DC filter as you suggested.

the amplifier works great when plugged directly into my phone. (with engine running )

but when the Bluetooth is powered up and plugged into the Amp the interference starts. its picking up the engine RPM's.

the Bluetooth receiver isn't designed for use in cars ..... ?


Good to hear :-)

Remember we covered conducted EMI which you have solved.

However there is still radiated noise RFI to contend or live with.

if i use the Bluetooth receiver powered through a laptop there is no noise whatsoever... strange

I assume the lap top is self powered.

yes, the laptop was just running off its battery.

You know how birds can sit on top power 2200 Volt AC wires.

Your laptop is a bird !

Maybe I could use a battery pack to power the Bluetooth receiver, I have rechargeable batteries. how much current do those receivers draw?

how to get 5 volts from 1.5 volt cells ?

would 3 AAA's be sufficient ?


Three cells start low at 4.5 volts and continue discharging down from there that Bluetooth receiver wont run very long as the voltage falls below 4.volts.

I would use 4 calls A,B or C in series with a single 1N4002 diode in series to lower the 5 Volts down to 5.5 volts DC.

Now ... you must learn how much current those Bluetooth receivers draw?

That will determine how long a pleasure of battery power can work for you.

on an other tack, I would attempt to place shield cables around your spark wire leads to minimize the RFI..

Are the speakers and radio stock or after market?

That EMI filter will not help at all. The interference is proabbly not coming through the power wires feeding the radio. If it's an after market radio than it may not have been installed and grounded correctly thus causing the interfearance.

how does one wire up a noise filter for 12 volt dc ? this item arrived with no instruction . thanks

Disconnect the plus + wire from the amplifier and twist connect it to the Blue input filter wire.

Then feed the Red output filter wire to the amplifier power plus.

Finally ground the Black negative filter wire to a strong metallic anchor point using sheet metal screw and a washer to make a very low resistance contact.

wire twist1.jpgSplicing with wire caps 3.JPG

Thanks for quick reply. am using a few components I threw together. they are connected to the same wires the original radio was. which didn't have any noise problems. could the quality of the amp be inferior? at the moment the Bluetooth isn't hooked up. trying to sort the noise out. using a 3.5mm jack from my phone.

This is the eBay amp I got : "Chip: TDA7297 Dual-Channel Amplifier Chip Power Supply: DC 9-18V, Recommend 12V 2A Output Impedance:4-8 ohms Efficiency: up to 90% Very easy to connect, please follow the picture to connect the Power Supply and Speaker. Size:L*W*H 50mm*48mm*43mm"

also got a better power supply for the Bluetooth receiver. will no longer use the cigarette lighter adapter

powersupply to bluetooth reciver.jpgBluetooth power supply.jpgBluetooth audio setup.jpg


the 12 dc filter arrived, but without instructions and no English, how does one wire them up ?


have removed the radio , in place a wideband 02 sensor controller.
the amp and Bluetooth are concealed behind.