Hey everyone, Today I am going to be writing about the Pre-Out voltages on a headunit.
What is a Pre-Out?
Basically almost every headunit you can buy now has a Pre-Out output on the back of it. Pre-out's are used to connect external amplifiers to the headunit to run things such as Sub-woofers, and High wattage speakers that the amplifier in the headunit just couldn't handle
Where do they come from?
Many head units have the Pre-out plugs on the back. The signal that comes out of them is Pre-Amplifier. Which means that the headunit hasn't amplified it to power speakers yet. It is also known as a Low Level output and the actual speaker outputs are classed as High Level outputs.
Different head units have different Pre-out voltages. Lower voltage Pre-outs will not mean that your amplifier will be quieter and High voltage Pre-outs do not mean they will be louder. The Pre-out voltage just helps to deal with the interference that you may pick up from the RCA cables. The higher the voltage of the Pre-out the better the signal will be at the amplifier end as more percentage of the output signal is music and less is interference.
Think of it like diluting a drink. If you have 2v of Pre-out voltage and then 0.5v of interference. You will get an RCA output that is 20% interference. If then you changed to a 4v output still with 0.5v of interference you would now only have 11% Interference. You could then lower the gain on the amplifier to match the higher voltage meaning that the interference would be a lot less intrusive into the music you are listening to.
As well as having a higher voltage Pre-Out there are other things that you can do to lower interference in the system.
1) Use good quality RCA cables.
One of the main reasons for bad interference is the use of cheap low quality RCA cables. These are the ones that generally come with amplifier wiring kits and can be bought as cheap as £2.50. A lot of the time the ends of the cables are not shielded for around the last 6cm and this can cause real problems when they are running close to power cables at the back of the headunit. It is best to pick up a fairly cheap Double Shielded cable which can be had for as low as £10. The difference in quality is usually very good and the general solidness of the cable is a lot better.
2) Run RCA signal cables away from the power cables.
This one is pretty simple a lot of the time. Basically when you are wiring up your system lay the power cables down one side of the car and any signal cables down the other. If possible also run the Remote cable from the headunit down the same side as the power as this also carried current. What happens if they are together is some of the voltage can be transferred to the signal cables and cause interference.
3) Make good earths for both the headunit and the amplifier
Most people when wiring an amplifier and audio system will find the easiest spot to earth the amplifier. This is not always the best place. When you are looking for an earthing spot always find the area that has the thickest possible metal and always remember to sand down the paint to get to the metal. Make it so that the metal is shiny and nice before bolting down your earth connector.
Secondly if you can make a specialized earth just for the headunit that would also make a difference to how much interference you get. Stock earth points for headunits are usually pretty crappy and can cause problems with high quality higher amp headunits. If you can cut and solder the earth cable and then mount it to a good clean metal spot on the car that could help to limit interference.
Basically that is all that I can think about at the moment but I will hopefully have some more stuff posted soon :)
Thanks for reading, Jack