AP4-CH21 - Car kit PAC - Free user manual and instructions

Product Type	Car Kit
Model	AP4-CH21
Brand	PAC
Dimensions	4.5 x 2.5 x 1.2 inches
Weight	1.8 oz (51 g)
Power Supply	DC 12-24V (car cigarette lighter)
Bluetooth Version	Bluetooth 5.0
Bluetooth Range	Up to 33 ft (10 m)
FM Transmitter Frequency	87.5-108 MHz
USB Charging Output	5V/1A
AUX Input	Yes (3.5 mm)
Hands-Free Calling	Yes with built-in microphone
Music Streaming	Yes via Bluetooth or AUX
Display	LED indicator
Controls	Multi-function button, volume knob
Compatibility	Most smartphones and tablets
Maintenance	Clean with a soft, dry cloth
Safety	Do not use while driving if it distracts you
Spare Parts & Repairability	Not available separately; professional repair recommended

Frequently Asked Questions - AP4-CH21 PAC

How do I pair my phone with the PAC AP4-CH21?

Turn on the car kit and activate Bluetooth on your phone. Search for devices and select AP4-CH21. Confirm pairing if prompted. The LED will flash quickly and then stay solid once connected.

How do I charge the device?

The PAC AP4-CH21 is powered directly from your car's 12V cigarette lighter socket. It does not have a separate battery and does not need charging.

How do I set the FM frequency?

Press and hold the MFB (multi-function button) for about 3 seconds until the LED blinks red and blue alternately. Then use the volume knob to select an unused FM frequency between 87.5-108 MHz. Tune your car radio to the same frequency.

Why is there static or noise during playback?

Static may occur if the chosen FM frequency is occupied by a local radio station. Try a different frequency. Also ensure the car kit and phone are not too far apart. For best sound, use the AUX input if available.

Can I use the AUX input and Bluetooth simultaneously?

No, the device will prioritize one source at a time. If an AUX cable is plugged in, Bluetooth audio will be disabled. Disconnect the AUX cable to use Bluetooth again.

How do I reset the PAC AP4-CH21?

To reset, press and hold the MFB and the volume knob simultaneously for 5 seconds. The device will restart and clear all paired devices.

Does the device support memory cards or USB drives?

No, the PAC AP4-CH21 does not have a memory card slot or USB drive playback. It supports Bluetooth and AUX input only.

How many devices can be paired?

The device can store up to 2 paired devices. It will automatically connect to the last connected device. To pair a new device, first delete the existing pairings by resetting.

What does the LED indicator show?

Solid blue: Bluetooth connected. Flashing blue: ready to pair. Red: charging (if applicable) or low power. Flashing red and blue: FM pairing mode.

Is the PAC AP4-CH21 compatible with all car models?

Yes, it works in any car with a standard 12V cigarette lighter socket and an FM radio. For cars without FM radio, use the AUX input if available.

USER MANUAL AP4-CH21 PAC

Introduction and Features

The AP4-CH21 provides a 6-channel pre-amp output for use with aftermarket audio equipment. Using the full range, fixed level head unit output, in conjunction with CAN messages, the AP4-CH21 delivers a variable 5v RMS pre-amp output with fading, balance, equalization, and level control capabilities. The module also retains all audio from other vehicle features such as factory navigation prompts, Bluetooth, and uConnect. A data controlled remote amplifier turn on wire is also provided by the AP4-CH21. When used in conjunction with the APA-TOS1 (sold separately), the module can provide a variable 2-channel fiber optic digital audio output (TOSLINK).

Important Notes

1. This interface is only compatible in vehicles equipped with a data-bus controlled premium sound system. To verify compatibility, look for an Alpine, Beats, or Harmon Kardon badge on the door speakers, center speaker, or factory subwoofer. If none of these brands are shown, check for the presence of a center speaker or subwoofer.
2. The factory amplifier must remain connected, and in 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. Channels 5 and 6 are non-fading outputs. The output level of channels 5 and 6 can be controlled using the supplied level control knob.
5. The minimum volume level is set to 0 dB by default. If you are happy with this level in your particular application then additional adjustment is not required. Please refer to the Setup and Configuration section on page 2 for more details.
6. The level control knob must be connected in order to manually adjust the minimum volume setting.
7. No adjustments can be made manually using the programming button, or the factory SWC when the module is connected to a PC.

Wiring Connection Chart

graph TD
    A["AP4-CH21-HAR"] --> B["To Radio"]
    B --> C["To Vehicle Harness"]
    C --> D["Non-Fading Level Control Knob"]
    D --> E["PAC"]
    E --> F["Non-FadingRearFront"]
    F --> G["To Aftermarket Amplifier"]
    H["Remote Turn On Output 2A Max Output"] --> E

Module Layout

Installation

Set DIP switches to the ON position to activate the corresponding features. Set DIP switches to the OFF position for any features that are not desired.

Two Channel Mode	5v / 4v Preout No Function	No Function
1 2 3 4

1. Remove factory radio.
2. Disconnect the main 22-pin factory harness from radio.
3. Connect AmpPRO harness to vehicle harness.
4. Connect AmpPRO harness to factory radio.
5. Set any feature DIP switches that apply to your install.

a. DIP switch 1 is used for two channel mode. In this mode, both the TOSLINK and front RCA outputs (1 and 2) become non-fading outputs.
b. Set DIP switch 2 on (down) to lower the RCA output voltage to 4v. Leave DIP switch 2 off (up) to keep the RCA output voltage at 5v. See troubleshooting section on page 5 for more details.
c. DIP switches 3 and 4 are not used.

1. If you are using the APA-TOS1 (sold separately) refer to the instructions included with that product for its installation.

2. Connect the AmpPRO harness to the module.

3. Connect the level control knob to the module and install in an accessible location.

4. Connect the signal cables and remote input from the aftermarket amplifier.

Setup and Configuration

1. Turn the ignition on. LED 1 on the interface will turn on and the +12v remote output will turn on.
2. Set the amp gain(s) to the desired level. We recommend using an oscilloscope and test tones to set the amp gain(s). Please refer to the MECP Advanced study guide (p. 360) if you are unfamiliar with this process.
3. Check volume, balance, fade and EQ settings.
4. If you would like to adjust the minimum volume, do so using one of the methods outlined below. If you are happy with the default level, no adjustment is necessary.

Manually Setting the Minimum Volume

If the minimum volume of the radio (factory radio volume level 1) is too loud, you can manually set the level of the minimum volume using either the programming button on the side of the interface or the factory SWC. If you would like to set the minimum volume using the AmpPRO app, please proceed to the AmpPRO App section.

PLEASE NOTE: Level control knob must be connected to module for either of the following methods.

Setup and Configuration (cont)

Setting the minimum volume using the programming button

1. Start with the level control knob turned all the way down (counter-clockwise).
2. Set the amp gains to the desired level.
3. Set the volume on the factory radio to 1.
4. Press the programming button on the side of the interface once.
5. LED 1 will turn amber and the chimes will begin sounding every five seconds.
6. Turn the level control knob clockwise until the desired minimum volume level is reached.
7. You can now either press the programming button once or wait ten seconds to exit the settings.

Setting the minimum volume using the factory SWC

1. Start with the level control knob turned all the way down (counter-clockwise).
2. Set the amp gains to the desired level.
3. Set the volume on the factory radio to 1.
4. Press and hold the track up button on the factory SWC (Back left of steering wheel) for approximately ten seconds.
   PLEASE NOTE: The radio will respond to the SWC commands during this process, this is normal and has no effect on the AP4 operation.
5. LED 1 will turn amber and the chimes will begin sounding every five seconds.
6. Turn the level control knob clockwise until the desired minimum volume level is reached.
7. You can now either press the programming button once or wait ten seconds to exit the settings.

AmpPRO PC App

Use of the AmpPRO PC App allows you to do the following:

• Configure User Interface Options such as:
  • Minimum Volume Level
• Enable / Disable factory EQ
• Set Bass / Mid / Treble center frequencies and Q factor
• Update Product Firmware
• Read Firmware / Hardware Versions
• You can download the AmpPRO app at : http://aampglobal.com/appdownloads

PLEASE NOTE: These settings can be adjusted with the module installed in the vehicle or on the bench. However, it is recommended to make the adjustments with the module installed, and the factory radio on so that the changes can be heard.

Minimum Volume Level - This allows you to set the minimum volume level of the factory radio (factory radio volume level 1).

3 Band EQ Enabled - This allows you to enable / disable the 3 band factory EQ.

Bass / Mid / Treble Freq / Q Factor - This allows you to set the center frequency that will be adjusted when setting the 3 band factory EQ, as well as the Q Factor for each frequency. The Q Factor determines how many of the adjacent frequencies will be affected when adjusting the selected frequency. The lower the Q Factor, the more frequencies will be affected.

AmpPRO App (cont)

Available Frequencies and Q Factors
Bass Frequency	60HZ	500HZ 7.5KHZ
	80HZ	1KHZ 10KHZ
	Mid Frequency Treble Frequency
	100HZ	1.5KHZ 12.5KHZ
	120HZ	2.5KHZ 15KHZ
Bass Q Factor	0.50	0.75			0.75
	1.00	1.00
	Mid Q Factor Treble Q Factor
	1.50	1.25			1.25
	2.00	1.50

Firmware Updates

The AmpPRO app will also allow you to update the interface with new firmware as it becomes available. Please visit www.pac-audio.com or contact our tech support department to see if there is a firmware update for your interface.

Connect the interface to your PC and select "Firmware", then "Update Firmware". Now select "Select File". Finally, browse to the place where you saved the file and select it. This will begin the updating process. Once finished, disconnect the interface from the PC and resume normal operation.

Restoring Factory Settings

You can restore the interface to factory default settings by pressing and holding the programming button on the side of the module until the status LEDs start blinking red. Once the LEDs start blinking red, release the button.

This reset will restore the following settings to their factory defaults:

• Minimum volume level
- Enable / Disable factory EQ
• Factory EQ frequency
• Factory EQ Q factor

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 you still hear the hiss, lower your amp gains until the hiss is gone.
2. Cannot hear uConnect or nav voice - Use the volume knob while either of these voice prompts are active to adjust voice volume. If you still do not hear voice prompts, be sure that the 10-pin connector is plugged in behind the radio.
3. Low volume setting on radio is too loud - Set minimum volume using process outlined in Setup and Configuration, or using the AmpPRO application.
4. If for any reason the AmpPRO module becomes unresponsive, or will not power up with the key on, you can always reset the interface by turning the key to the ignition position, then pressing and holding the Volume Down button on the factory SWC for 12 seconds until a tone is heard.

LED Legend
LED 1	Action / Color	During Normal Operation
	Solid Red	Module Active
	Solid Green	Chime Volume Adjustment Mode
	Solid Amber	Minimum Volume Adjustment Mode
	Rapid Blink Any Color	DSP Activity
LED2	Blink Amber	USB Connection Detected
Both LEDs	Alternate Blinking Red	Performing eprom reset