GTMEDIA A4 USB Bluetooth 5.1 Wireless Audio Adapter

1. Introduction

The GTMEDIA A4 is a versatile Bluetooth 5.1 audio adapter designed to function as both a receiver and a transmitter. It offers broad compatibility with various devices such as mobile phones, tablets, car audio systems, computers, televisions, and older speaker setups. This device enables seamless audio sharing for different environments, whether for study, daily living, or work.

2. Package Contents

Please check the box for the following items:

• 1 x Bluetooth audio adapter (GTMEDIA A4)
• 1 x AUX 3.5mm audio cable
• 1 x RCA 1 to 2 to AUX 3.5mm audio cable
• 1 x USB-C charging cable
• 1 x Fiber optic cable
• 1 x Antenna
• 1 x Remote control
• 1 x User Manual

3. Product Overview

The GTMEDIA A4 features a compact design with multiple input and output options to suit various audio setups. Familiarize yourself with the device's ports and controls:

Figure 3.1: GTMEDIA A4 Device and Remote Control Layout
This diagram illustrates the various input and output ports on the GTMEDIA A4, including USB, TF card slot, DC 5V power, AUX, RCA (R-AUDIO-L), Coaxial, Optical, and Antenna. It also shows the front panel controls such as POWER, TX/RX, TF/USB, DAC/AUX indicators, H/RX, M/TX, MODE buttons, IR receiver, and Volume adjustment/Power switch. The remote control layout with buttons for volume, mode, track control, and number keys is also depicted.

Front Panel Controls:

• POWER Indicator: Shows power status.
• TX/RX Indicator: Indicates Transmit (TX) or Receive (RX) mode.
• TF/USB Indicator: Indicates TF card or USB disk playback mode.
• DAC/AUX Indicator: Indicates Digital-to-Analog Converter or AUX mode.
• H/RX Button: Previous track / RX mode switch.
• M/TX Button: Next track / TX mode switch.
• MODE Button: Switches between operating modes.
• IR: Infrared receiver for remote control.
• VOL Knob: Rotary knob for volume adjustment and power on/off.

Rear Panel Ports:

• DC 5V (USB-C): Power input port.
• AUX (3.5mm): Analog audio input/output.
• R-AUDIO-L (RCA): Analog audio input/output.
• COAXIAL: Digital coaxial input.
• OPTICAL: Digital optical input.
• ANTENNA: External Bluetooth antenna connector.

4. Setup Instructions

4.1 Initial Setup

1. Charge the Device: Connect the provided USB-C charging cable to the DC 5V port on the A4 and to a 5V USB power adapter (not included). The device has a built-in 800mAh battery.
2. Install Antenna: Screw the external antenna firmly into the ANTENNA port on the rear panel.
3. Power On: Turn the VOL knob clockwise to power on the device.

4.2 Bluetooth Receive Mode (RX)

Use this mode to receive audio wirelessly from your phone or tablet and output it to wired speakers, headphones, or car audio systems.

1. Connect to Audio Output:
   • For active speakers, headphones, or car stereo: Connect the A4's AUX or RCA output to your audio device's input using the appropriate audio cable.
   • For digital audio systems: Connect the A4's Optical or Coaxial output to your audio device's digital input.
2. Select RX Mode: Press the MODE button on the A4 or the remote control until the RX indicator lights up.
3. Pair with Bluetooth Device: On your phone or tablet, enable Bluetooth and search for available devices. Select "GTMEDIA A4" from the list to pair.
4. Play Audio: Once paired, play audio on your phone/tablet, and it will be transmitted to your connected audio system via the A4.

Figure 4.1: Bluetooth Receive Mode Connections
In Bluetooth Receive (RX) mode, the GTMEDIA A4 can connect to your existing audio systems. Use the appropriate cable (AUX, RCA, Coaxial, or Optical) to link the A4 to devices such as active speakers, headphones, an amplifier, or your car stereo. Your mobile device (phone or tablet) then connects wirelessly to the A4 via Bluetooth.

4.3 Bluetooth Transmit Mode (TX)

Use this mode to transmit audio wirelessly from a wired audio source (e.g., TV, PC) to Bluetooth headphones or speakers.

1. Connect to Audio Source:
   • For TV, PS/XBOX, TV box, DVD: Connect your audio source's audio output (e.g., AUX, RCA, Optical, Coaxial) to the corresponding input on the A4.
2. Select TX Mode: Press the MODE button on the A4 or the remote control until the TX indicator lights up.
3. Pair with Bluetooth Headphones/Speakers: Put your Bluetooth headphones or speakers into pairing mode. The A4 will automatically search and connect to nearby Bluetooth audio devices.
4. Play Audio: Once connected, audio from your source device will be transmitted to your Bluetooth headphones/speakers.

Figure 4.2: Bluetooth Transmit Mode and Digital to Analog Conversion
In Bluetooth Transmit (TX) mode, the GTMEDIA A4 connects to audio sources such as a TV, PlayStation/Xbox console, TV box, or DVD player using AUX, RCA, Coaxial, or Optical inputs. It then wirelessly transmits the audio to Bluetooth headphones or a Bluetooth stereo system. The diagram also illustrates digital-to-analog conversion where digital inputs (Coaxial, Optical) are converted to analog outputs (RCA, AUX) for connection to active speakers, amplifiers, or car stereos.

4.4 U-disk / TF Card Playback

The A4 supports direct audio playback from a USB flash drive (U-disk) or a TF (MicroSD) card.

1. Insert Storage Device: Insert your U-disk into the USB port or your TF card into the TF slot on the front panel.
2. Select Playback Mode: The device should automatically switch to TF/USB playback mode. If not, press the MODE button until the TF/USB indicator lights up.
3. Control Playback: Use the H/RX (Previous), M/TX (Next), and MODE (Play/Pause) buttons on the device, or the corresponding buttons on the remote control, to manage playback.

Figure 4.3: U-disk and TF Card Slots with Volume Control
The GTMEDIA A4 supports direct playback from a U-disk (USB flash drive) or TF card. Simply insert your storage device into the designated slot. The device also features an independent volume adjustment knob for precise audio control.

5. Operating Instructions

The GTMEDIA A4 can be operated using the physical buttons on the device or the included infrared remote control.

5.1 Power On/Off

• Device: Turn the VOL knob clockwise to power on, counter-clockwise to power off.
• Remote Control: Press the power button on the remote.

5.2 Mode Switching

• Press the MODE button on the device or remote to cycle through RX (Receive), TX (Transmit), and U-disk/TF card playback modes.

5.3 Volume Control

• Device: Rotate the VOL knob to adjust the volume.
• Remote Control: Use the VOL+ and VOL- buttons.

5.4 Playback Control (U-disk/TF Card)

• Previous Track: Press the H/RX button on the device or the button on the remote.
• Next Track: Press the M/TX button on the device or the button on the remote.
• Play/Pause: Press the MODE button on the device or the button on the remote.

6. Specifications

Figure 6.1: GTMEDIA A4 Product Parameters

Figure 6.2: Battery Performance
The GTMEDIA A4 is equipped with an 800mAh polymer battery, offering approximately 300 hours of standby time, up to 7 hours of continuous use, and a charging time of about 2 hours.

7. Maintenance

• Keep the device dry. Avoid exposure to moisture or liquids.
• Clean the device with a soft, dry cloth. Do not use harsh chemicals or abrasive cleaners.
• Avoid exposing the device to extreme temperatures (hot or cold).
• Do not attempt to disassemble or modify the device, as this will void the warranty.
• Store the device in a cool, dry place when not in use.

8. Troubleshooting

No Power / Device Not Turning On:

Ensure the USB-C charging cable is securely connected to the DC 5V port and a working power source. Check if the internal battery is charged.

Unable to Connect via Bluetooth:

• Verify the A4 is in the correct mode (RX for receiving, TX for transmitting).
• Ensure the A4 and the paired device are within the 15-meter transmission range.
• Make sure there are no significant obstructions between the devices.
• Check if the A4 is already paired with another device. Disconnect if necessary and try pairing again.
• Restart both the A4 and the Bluetooth device.

No Sound Output:

• Check all audio cable connections (AUX, RCA, Optical, Coaxial) to ensure they are secure and connected to the correct input/output ports.
• Adjust the volume on both the A4 and the connected audio device.
• Ensure the correct input source is selected on your connected audio system.
• Verify the A4 is in the appropriate mode (RX/TX) for your setup.

Remote Control Not Working:

• Ensure there is a clear line of sight between the remote control and the IR receiver on the A4.
• Check the battery in the remote control and replace if necessary.

9. User Tips

• For optimal Bluetooth performance, ensure the adapter is within 15 meters (approximately 49 feet) of the connected device and free from major obstructions.
• When using U-disk or TF card playback, ensure your audio files are in supported formats (MP3/APE/FLAC/WAV/WMA).
• To upgrade older speakers to Bluetooth functionality, connect the A4 to the speaker's AUX/RCA input and use the A4 in RX mode.
• Utilize the independent volume control knob on the device for quick adjustments, or the remote for convenience from a distance.

10. Warranty and Support

The GTMEDIA A4 USB Bluetooth 5.1 Wireless Audio Adapter comes with a 1-year limited warranty from the date of purchase. This warranty covers manufacturing defects and workmanship under normal use.

For technical support, warranty claims, or any inquiries regarding your product, please contact your retailer or visit the official GTMEDIA support website for assistance. Please have your purchase receipt and product model number (A4) ready when contacting support.