Interfacing an amplifier with an OEM system

How do I interface my Rockford Fosgate amplifier with an OEM (Original Equipment from Manufacturer) system?

Factory Source Unit Output Power 

Most factory source units make between 3 to 13 Volts A/C on their speaker-level outputs (2 to 42 watts with 4-ohms resistance), not including the factory amplifier. A factory amplifier can make the signal voltage jump from 10 to 20 volts A/C (25 to 100 watts at 4-ohms)! You can verify this by playing a test tone through the system and measuring the output with a multi-meter.

High/Low Level 

Since we know that most high-end aftermarket source units make 4-volts A/C on their pre-amp outputs, you can immediately see that line-level outputs from any factory source unit or amplifier are much higher in voltage than most pre-amp RCA outputs. Because of the problem of trying to integrate aftermarket amps to factory source units, manufacturers introduced high-level inputs on their amps, and other manufacturers made high-to-low-level converters. Both act in the same way - to reduce signal voltage by providing higher resistance and lower sensitivity.

Amplifier Input Voltage 

Most all Rockford Fosgate amplifiers handle up to 4-volts of input on the RCA's, and up to 11 volts on the high-level inputs, we know that any signal greater than that will cause the amplifier to "clip". Adjusting the Gain controls all the way down to their least sensitive 4-volt setting will help, but will not solve the problem of too much signal input.

Amps shutting down 

Factory systems will "peak" at higher voltages then many of the converters can accept. When this happens, it passes the additional voltage right to the amplifiers, causing the amplifier to "clip" due to the increased signal voltage input. This clipping can cause the amplifier to heat up, and potentially shut down or turn off briefly.

NOTE: In some cases, you cannot use converters or the amplifier's high-level inputs due to the power levels coming from the factory system. The only way to make it work at that point is to switch head units to an aftermarket one with dedicated low-level RCA outputs.

Interfacing An Amplifier To A Factory System 

OEM Factory sound systems are getting more difficult each year to interface with. Many of these new systems are very complex and control multiple components in the car. In the next 10 years this problem will certainly intensify with new car options like on board computers, email, streaming music the list goes on. 

Fortunately for us, the one technology that probably won’t change too much in the near future is the speaker. The speaker leads provide you with a safe connection point for the audio signal without the inherent danger of damaging the factory components. It is recommended that you use a high quality transformer isolation converter commonly called a “line output converter” (LOC) or a “high to low level adapter”. 

A high quality LOC will have a very high input impedance (20,000 ohms) which allows for a noise free integration as well as a safe impedance load to the factory source unit. For improved noise isolation, it is also recommended to use high quality unshielded twisted pair cable when connecting the LOC to the factory speaker leads.

Attaching an amplifier to a factory system that has no aux outputs.

Connect unshielded twisted pair cable from the factory speaker to the high/low converter. Place the high/low converter as close to the amplifier as possible.

High Level Input Polarity 

Punch series amplifiers are equipped with a high level input. Basically the high to low converter is built into the amplifier eliminating the cost of addition components when connecting a Punch amplifier to a factory system. This method of attaching the amplifier is a relatively easy task except for deciphering which of the multicolored factory speaker leads are positive or negative.

The easy way to determine which factory wires are positive or negative.

Disconnect a factory speaker. Using a 1.5 Volt DC battery, attach it to the speaker in the direction that pushes the speaker cone out. Note that if the BLUE wire is connected to the plus (+) terminal of the 1.5 Volt battery when the speaker moves out, then the BLUE wire from the factory source unit will be the positive input for that channel of the amplifier. The PINK wire will obviously be the negative input for that same channel. Repeat the process for the other channels

Remember: Rockford Fosgate Authorised Dealers are Experts at installation of Aftermarket Audio Upgrades! If you're not sure how to perform your installation, refer the installation and system design to the professionals!