(Amplifier Interface Circuit)
Before people get to posting things saying that you can just use a 7805 voltage regulator instead of what I sell, well you can. Actually that's exactly what I sell.
Here is the schematic of what this device is.
This is taken right out of a 7805 datasheet and is what is required for these parts. They were designed to have the capacitors on the inputs and the outputs. If these are not there the output will oscillate (or ring) which is not good for sensitive electronic equipment. You won't see it on a volt meter, they are too slow (and average the voltage measured over time). But if you look at the output on an oscilloscope you will see a high frequency oscilation on the output if you do not use the capacitors specified in the datasheet for your 7805.
So feel free to make one, I believe most electronics supply shops have this stuff in stock. Just make sure the regulator you choose has enough supply current to power your vehicle's amplifiers or is at least as strong as the supply current out of the head unit you are using.
Do you even need one of these?
Well as I said in the product page, there are a few things which can cause a popping sound with amps. I'll post some links to other pages at the bottom of this page.
When I was researching this problem I had with my 2003 Lincoln Aviator, most of the help I got was to either put a resistor on the amplifier turn-on line between the head unit and the car's wiring or delay the turn on with a circuit.
I thought the resistor was easier so I tried it and it didn't work. I heard people say to try a 1K or a 2K resistor to "limit the current" on this line. That didn't work for me. If you really want to try it, feel free, but I would recommend against doing this. At best it's a band-aid fix for the problem. I really don't hold too much stock in this theory. I almost didn't mention it here, but since I found this theory on line I included it.
By far the most common reason people will say amplifiers will "pop" when the car turns on is that there is no audio signal going to the amps when they are turned on. The amps turn on too soon with no audio signal and when the audio signal finally is sent to the amps, the sudden signal from nothing causes a pop. Sounds pretty good right? There are a ton of people out there to sell delay turn-on circuits. I almost bought one. But this solution is more for vehicles with aftermarket amplifiers, not factory amplifiers. Before you buy one and waste your money, you can test it to see if this is the problem.
If you want to test if this is your problem, you will have to work on your radio with the radio out or with access to the wiring. Do this at your own risk, if you have any concerns about your knowledge or skill working around electronics, let a professional work on your car. It's better to pay someone a few bucks then end up ruining your new radio or car or both.
Hook up the head unit with all the connections as you normally would only do not connect the amp turn-on wire from the head unit to your vehicle's wiring. Make sure you have access to the amp turn-on wire from your head unit and the vehicle. Do not connect them yet, strip the ends of the 2 wires (the amp turn-on wire out of the head unit and the amp turn-on wire into your vehicle's wiring). Make sure they don't short to anything, and leave them loose. Then turn on your vehicle. The radio will turn on. Give it a few seconds (this depends on the head unit). Make sure a few seconds have passed so that audio will be playing. If the amp is only powering a subwoofer, you should hear music out of the stock speakers. Then connect the 2 bare wires (the amp turn-on wires). Make sure they touch. You can hold the copper with your fingers, it won't hurt you. Just make sure there is a good connection. Your amplifier should turn on.
If it turns on and plays music and there was no pop, then you need one of the delay turn-on circuits. I don't know any to recommend, just poke around the internet. Lots of people sell them.
If music was playing before you connected the 2 wires, and when you did there still was a pop when they turned on, the delay circuit WILL NOT fix your problem. It could be caused by the improper voltage going to the amplifier. If so then one of my circuits would fix this. I know this is what I needed for my Ford product. Other ford products probably function the same way. Some other vehicles might as well.
Links I found about delay turn-on circuits