Connecting your stock/factory head unit to an aftermarket amplifier

Many times, the speaker level input of an amplifier will be poorly designed and will cause noise problems.

Click to expand...

Line Output Converters

Function:
Line output converters are used to convert a head unit's (HU) speaker outputs into a signal suitable to drive the preamp inputs of an amplifier. Most line output converters (LOCs) used in the past few years are designed for high output HUs.

Background:
The speaker output of a high powered HU is designed to operate in a bridged configuration. The output speaker wires each have half of the DC battery voltage on them when the HU is on. When the HU is off, the voltage on the output wires is 0 volts DC. When the HU is switched on, the DC voltage instantly changes from 0 volts DC to 1/2 of the battery voltage.

Construction:
A high powered LOC consists, primarily, of a transformer and a high power (10 to 20 watts) resistor. The resistor is used to load the amplifier in the HU. Some amplifiers will exhibit less than ideal manners when they are unloaded. Remember that we said that the HU's outputs had a large quick increase in DC voltage when the HU is switched on. The transformer will pass the difference in voltage between the two input terminals. Since the DC voltage increases simultaneously on both of the input terminals, the pulse of DC is canceled out. If the LOC simply used resistors as a voltage divider (with no transformer), the turn on pop would be severe.

Note. The transformer also gives you a clean ground which wasn't available from the bridged outputs of the head unit.

Shield ground wires:
There are usually 1 or 2 extra wires on a LOC. These wires are used to ground the shield of the RCA output cables to the HU. Some amplifiers work fine without them, others don't. If the LOC is installed behind the radio, I would recommend connecting the shield ground wires to the case of the radio.

Click to expand...

If you use an LOC, you will have to set the gains on your amplifier so that the amplifier reaches full power before your head unit's volume control reaches 1/2 volume. Most radios' speaker outputs will start to clip at about 1/2 volume. This is far earlier than the point where the preamp output signal starts to clip on most radios. The only time that I've seen a preamp out start to clip along with the speaker output is when the preamp output signal is derived from the speaker output via a voltage divider network (sort of a cheap internal LOC). This is usually only done on the bottom_of_the_line head units. What is clipping?http://www.bcae1.com/amplfier.htm#clipping

Click to expand...

If you have a factory/stock head unit that you are connecting this amplifier to, you'll need to either use high-level-inputs or a LOC (aka line out converter or line level converter). If you want to connect it through high-level-inputs you'll need to check if your amplifier has that specific feature. If it does, REMOVE THE HEAD UNIT and then you'll need to tap/splice into the speaker wires to get the signal. DO NOT cut the speaker wires, just splice into the rear or front speakers and then run the wire bad to your amplifier's high-level-input area. For your speaker wire colors go HERE Personally, I always recommend going with a quality LOC instead of using high-level-inputs because, at the current time, many amplifier manufactures use poorly built high-level-inputs in their amplifiers and it degrades the signal quality. The only time I'd recommend using high-level-inputs would be if it's a subwoofer amplifier. I say this because subwoofers cover a smaller range of frequencies so the signal degration isn't as noticeable compared to if you were running full-range/full-bandwidth speakers. If you want to insure a quality signal of your factory head unit, I usualy recommend DAVID NAVONE PRODUCTS. David Navone makes very very quality items while keeping them affordable by offering various types of LOC's. From what I've gathered, brands from Wal-Mart or a similar store (such as the Scosche brand) are generally bad quality and can induce noise into your system. Connecting a LOC to your head unit isn't too complicated. Just use a razor to splice off a small section (about a centimeter) of insulation of the wire you will be tapping into. Use a pointy object to part the wire in the middle. Strip at least a centimeter, if not more, of insulation off the end of the LOC wire and twist the bare wire end. Then slip it between the parted speaker wire and tightly twist it around the speaker wire so it's very secure. If you have a solder gun I highly recommend that you, next, solder this connection. Repeat for all the LOC wires. If you have a LOC with a black wire and it's specified as a ground connection, DO NOT connect it. In most cases, this wire is to only be used if you are getting noise in your system. If you do get noise in your system and you are positive it isn't a bad amplifier ground or something else, connect the black ground wire(s) (some have two of these wires) to the head unit casing. To do this, put a ring terminal on the wire(s) and use the nut and bolt on the rear middle of the head unit to hold it on the radio casing. Again, using a bare metal washer is a good idea.

Click to expand...

sa_pyro_ne said:

If you don't have the blaupunkt MP3 head unit (installed by ford from the factory) or the 9006 Audiophile head unit, you have no way of getting a signal for your amplifier to reproduce unless the signal goes through a LOC (line output converter aka line level converter) or high-level-inputs (aka speaker level inputs). I suggest going with a quality LOC over using high-level-inputs because of this quote from www.bcae1.com :

Click to expand...