Sometimes, when you turn on the radio in your Volvo, you might hear the sound of the engine (or any other sound) via the speakers of the radio. This is often caused by the following:
- The dynamo
- The spark plugs and cables
- The distributor cap
- The board computer/ECU
- The earthing loop
Firstly, always connect the radio/ directly to the +pole of the battery with a standard noise suppression kit (if possible).
1. Alternator disturbance:
Problem: a screeching whistle through the radio/amplifier which varies in pitch with the revs of the car.
Solution: Capacitor over alternator windings to earth. 10nF to 100nF should be sufficient.
2. Spark plugs and cables:
Problem: often a ticking sound in your radio/amplifier which varies with the revs of your car, the frequency is often 1/4 of the rpm, only with stroke of ignition
Solution: special spark plug cables and spark plug caps. Screw noise suppression filters into the spark plug cable, which consists of a R/L/C-combination
3. Distributor cap:
Problem: the distributor cap can disturb the radio in the same way as the spark plug cables.
Solution: Use a good cable that leads to the coil. Also here you can add nois suppression filters, if necessary
4. board computer/ECU
Problem: disturbance via the board computer will hardly ever occur
Solution: if it does, then put Cs over the injector
5. earthing loop:
Problem: sometimes one forgets to earth the radio/amplofier. Earthing then goes via the antenna connection, which will create an earthing loop.
Solution: immediately earth the radio/amplifier via the -pole of the battery. This often solves the problem.