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Pc In My Car - Question About Noise In Speakers

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Hi to every body !

Sorry for my english. So I am in Canada. I have RX300, 99. Good car. One day I installed PC in my car. Fotos will follow. Shortly: EFIA 1000MHz, GPS, WLAN, OBDII diagnostic, etc. Everything is installed under the dash. I used regular powersuply PW70 for the car. So everything is working good. GPS, Internet, OBD, etc. One small problem: when I trying to play MP with WINAMP or any sound - I can hear a noise from PC and from car alternator in my speakers. How I connect audio: PC sound card output connected to the FM modulator, and after on FM88.3 it goes to the CAR AUDIO. Tell me, is any possibility to connect directly to the car amplifier ????? Where the inputs, how to find them, how I can get a schematic. Second question - how to reduce the noise - any schematic of the good filter between PSU and car Battery ??? And how did you fix this problem ? Becose to listen music with this noise is realy difficult.

This is FM MODULATOR which I am using:

This is PSU which I am using:

Thank you for your help


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the FM modulator is most likley to blame, Im using a Tape adapter, not ideal but it was far better than the FM modulator i was using, also Im using an Opus psu to power my epia as the pw 70 i was using didnt always get enough power to stop the pc from rebooting.

as for the alternator problem, is your psu for the computer connected directly to the Battery? or is it coming from the ignition?

also I have heard something about a ground loop isolator, but I really dont know what it is or what it really does, but I have heard them being used to rid the alternator noise.

hope its of some help

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Not sure of the Amp in the RX, but here's a few things you can to try and get rid of the whine.

Firstly, establish if the whine is RF based or coming through the power leads. Plug some heaphones into the output of your PC - if the whine is still there then it will be coming through the power supply. You can double check by plugging your modulator into a walkman or similar Battery powered device. If the whine is not there, it will confirm it.

Steve is correct is suggesting an isolation problem, but it could be that your DC-DC converter is using a switched mode power supply that is isolating already, making a potential difference on the audio common. Try the PC itself with a good ground to the vehicle body earth AFTER the power supply.

You can also use an inductor around the output leads of power feed to the PC. (again, AFTER the PSU) This can be a simple ferrite ring (can be bought from electronics stores) creating an inductor in series with the circuit. This induces a magnetic field in the ferromagnetic material of the core. This magnetic field raises the impedance and effectively blocks noise currents from the alternator.

This could also indicate a diode is on it's way out in the alternator.

If any of these are the case, then because PC will be more suseptible to the noise, you may find that connecting directly to the amp will still leave you with a whine. (Although that is always going to sound better than a modulator)

If the whine is RF based, again there could be a difference in the earth - is the 12v supply to the modulator from the output of the car PSU or the input side? Try and match these by putting it on the output side if possible.

You can't go that far with RF based problems as it gets very complex and probably not worth it if you can connect to the amp. I take it you have tried a different frequency? (Assuming your unit supports it)

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