AP4-GM81 Advanced Amplifier Interface for General Motors

Introduction and Features

The AP4-GM81 provides a 6-channel pre-amp output for use with aftermarket audio equipment. It delivers a variable 5v RMS pre-amp output with fading, balance, equalization, and level control capabilities. The module retains all audio from other vehicle features such as factory navigation prompts, Bluetooth, OnStar, and parking sensor chimes. A data-controlled remote amplifier turn-on wire is provided. The module also offers a variable 2-channel fiber optic digital audio output (TOSLINK).

Important Notes

1. This interface is only compatible with vehicles equipped with a BOSE factory amplifier (RPO code UQA or UQS).
2. The factory amplifier must be disconnected and removed from the vehicle after the AmpPRO has been installed.
3. The remote output is rated at 2A of current. If more current is needed, an external relay must be used.
4. The remote output is active any time the vehicle data bus is active. Any vehicle interaction, like opening a door or pressing a button on the key fob, will activate the data bus.
5. Channels 5 & 6 are non-fading outputs. Their output level can be controlled using the supplied level control knob.
6. When the non-fading level control knob is not connected to the AP4-GM81, the output level of channels 5 & 6 will default to 100 percent.
7. To adjust minimum volume without using the PC App, the level control knob must be connected.
8. While adjusting the minimum volume with the USB cable plugged in, the level control knob will not function.
9. To adjust chime volume, the PC App must be used.
10. Chime volume (Front & Rear) can be adjusted through the OE Radio under "Settings > Vehicle > Comfort and Convenience > Chime Volume." Before making additional chime volume adjustments with the PC App, set the OE volume to the middle.
11. The chime volume and minimum volume levels are set to a typical level by default. If you are satisfied with this level, no further adjustment is required. Refer to the Setup and Configuration section for more details.
12. Front and rear chimes are independently adjustable to compensate for differences in power levels between front and rear installations.
13. The factory radio's speed-controlled volume and surround sound mode are not supported by the AP4 outputs.
14. When using the TOSLINK output, all chimes must be routed through the front output by setting DIP switch 1 ON (down).
15. No adjustments can be made manually using the programming button or the factory SWC when the module is connected to a PC.
16. The AP4-GM81 is designed to be installed in the factory amplifier location, NOT behind the radio. It will replace the factory amplifier, which will no longer be used.

Module Layout

The module features:

• Feature Select DIP switches
• Non-Fading Level Control Knob Connection
• Expansion Port
• Programming Button
• USB Connection
• Interface Connector 1
• TOSLINK Output
• Front Output: Ch. 1(L) and 2(R)
• Rear Output: Ch. 3(L) and 4(R)
• SUB (Non-Fading): Ch. 5 and 6
• LED 1 and LED 2 indicators

Installation

1. Access the factory amplifier.
2. Disconnect all harnesses from the factory amplifier.
3. Connect the AmpPRO harness to the vehicle amplifier harness.
4. Set feature DIP switches as needed:
   • DIP switch 1: For two-channel mode. In this mode, both the TOSLINK and front RCA outputs (1 and 2) become non-fading outputs. All rear chimes will also be routed through these outputs.
   • DIP switch 2: Set ON (down) to lower the RCA output voltage to 4v. Leave OFF (up) for 5v output. Refer to the troubleshooting section for details.
   • DIP switches 3 & 4: Not used.
5. Connect the AmpPRO harness to the module.
6. Connect the level control knob to the module and install in an accessible location.
7. Connect the signal cables and remote output to the aftermarket amplifier.
8. Turn the vehicle off, shut the doors, and lock the vehicle with the factory key fob. Wait 5 minutes.
9. After 5 minutes, turn the vehicle back on. LED 1 on the interface will illuminate, and the +12v remote output will turn on.
10. Set the amplifier gain(s) to the desired level. It is recommended to use an oscilloscope and test tones for setting amplifier gains.
11. Check volume, balance, fade, and EQ settings.
12. Check the chime volume levels for the front and rear chimes. If the default levels are satisfactory, no further adjustments are needed. Proceed to Setup and Configuration if adjustments are required.

Setup and Configuration

Step 1: Set Minimum Volume

If the minimum volume of the radio (factory radio volume level 1) is not suitable, you can set the level using the programming button, steering wheel controls, or the PC App.

Setting minimum volume using the PC App (connected via USB):

1. Set the volume on the factory radio to 1.
2. Adjust the "Minimum Volume Level" slider to the desired level.

Setting minimum volume using the programming button:

1. Start with the level control knob turned fully counterclockwise.
2. Set the volume on the factory radio to 1.
3. Press the programming button on the side of the interface once. LED 1 will turn amber, and chimes will sound every five seconds.
4. Turn the level control knob clockwise until the desired minimum volume level is reached.
5. Wait ten seconds to complete the process.

Setting minimum volume with factory steering wheel controls:

1. Start with the level control knob turned fully counterclockwise.
2. Set the volume on the factory radio to 1.
3. Press and hold the track up button on the radio's steering wheel controls for approximately ten seconds. Note: The radio will respond to SWC commands during this process, which is normal and does not affect AP4 operation.
4. Chimes will begin sounding every five seconds.
5. Turn the level control knob clockwise until the desired minimum volume level is reached.
6. Wait ten seconds to complete the process.

Step 2: Chime Volume Adjust

If chime volume adjustment through the OE Radio (Settings > Vehicle > Comfort and Convenience > Chime Volume) does not provide a suitable range, use the PC App. Front and rear chimes can be adjusted independently to account for differences in aftermarket system gains.

1. Set the chime volume to the midpoint on the OE radio before adjusting sliders in the PC App. This allows for later adjustment up or down in the OE radio.
2. By default, front and rear chimes are set at 55.
3. Adjust the "Chime Volume Adjust" slider to the desired level for front and rear chimes.

Step 3: OE EQ Settings

EQ Enabled: Allows you to enable or disable the 3-band factory radio EQ.

Bass / Mid / Treble Freq / Q Factor: Allows you to set the center frequency and Q Factor for each band of the factory EQ. The Q Factor determines how many adjacent frequencies are affected when adjusting a selected frequency; a lower Q Factor affects more frequencies.

Restoring Factory Settings

You can restore the interface to factory default settings by pressing and holding the programming button on the module until the status LEDs start blinking red. Release the button once the LEDs begin blinking red. This reset restores the following settings to their factory defaults:

• Chime volume levels
• Minimum volume level
• Factory EQ Settings

Troubleshooting

1. Hiss at high amp gain: Set feature DIP switch 2 to the ON (down) position to lower the output voltage of the AP4 to 4v. If hiss persists, lower your amplifier gains until it is gone.
2. Cannot hear OnStar or Nav Prompts: Use the OE volume knob or head unit volume knob while these features are active to adjust their volume.
3. Cannot hear chimes: Adjust chime volume using the process outlined in the Setup and Configuration section.
4. Low volume setting on radio is too loud: Set the minimum volume using the process outlined in the Setup and Configuration section.

Firmware Updates

The AmpPRO PC App allows you to update the interface with new firmware as it becomes available. Visit www.pac-audio.com or contact PAC technical support to check for firmware updates.

To update:

1. Connect the interface to your PC.
2. In the AmpPRO PC App, select "Firmware," then "Update Firmware."
3. Select "Select File," browse to the location where the firmware file was saved, and select it. The update process will begin.
4. Once finished, disconnect the interface from the PC and resume normal operation. Ensure you wait for the "Update Complete" message before disconnecting, even if the progress bar has reached the end.

LED Legend

Wiring Connection Chart

The wiring diagram illustrates the connections between the AP4-GM81, the vehicle amplifier harness, and the aftermarket amplifier. It details connections for 16-pin and 8-pin amplifiers, speaker leads, and the TOSLINK output.

The remote amplifier turn-on is rated at 2A max output.

Speaker ID Chart

Use this chart to identify speakers in your vehicle using a tone generator to ensure proper connections and polarity. Not all applications will utilize all wiring in this chart.