Circuit for Audio Splitter

In general all laptops contain one audio port, and whatever may be the audio devices it should be connected to that single port. Assume that you are playing a game on your pc or laptop in multi mode with a friend during night hours and you don’t want to disturb your parents by switching your speaker on, preferably the choice would be to use a headphone. It is annoying to share the earpiece of headphone, while missing all the sound effects. The circuit given here describes a simple audio splitter which could be easily made and installed and only cost a little. The audio splitter comes with separate volume controls for each headphone.

Circuit Description

This active splitter for laptop audio-out is powered from a USB and provides individual channel gain of 39 dB and individual volume control of a headphone channel. The circuit uses two TDA2822M audio power amplifier ICs for headphones / small speakers. Each 8-pin DIP TDA2822M has two audio power amplifiers: one to serve the left channel, and the other for the right channel (stereo). Therefore to get a two-headphone output, you require four amplifiers ortwo pieces of TDA2822M.The TDA2822M can operate over a voltage range of 1.8V to 15V. The USB port provides 5V and 100mA current, which is more than enough for two pairs of headphones. The circuit comprises four symmetric Sections, each section using half of TDA2822M. The input left and right channels for both the ICs are connected together. That is, the IN(R) of IC1 is connected to IN(R) of IC2. The same applies to the left-channel inputs too. The amount of input signal entering the ICs is controlled by the voltage divider for each channel input: four 47-kilo-ohm potentiometers are used for the four power amplifiers. Since the input resistance of the IC is very high, the effective load at the output port of the laptop is 47 kilo-ohms/ 2= 23.5 kilo-ohms. This does not, in any way, load the audio-out port. The signals that finally reach pins 6 and 7 of the IC are amplified with a voltage gain of about 89, and the amplified signals are fed to the headphones via 470μF electrolytic capacitors. The combination of 0.1μF capacitor and 4.7-ohm resistor helps in reducing the high-frequency noise and lower the possibility of oscillations. The 100 μF at pins 5 and 8 provides AC grounding at audio and higher frequencies. The 10μF capacitors at the Vcc pins suppress the line noise.

Circuit Power

On stripping the outer sheath of the USB cable, you will find five wires (sometimes four). These wires are red, green, white, black (thick) and black (thin) in colour. One of the blacks may be absent in four-wire versions. The red wire provides +5V, while the thick black wire must be used for the ground. In case the thick black wire is absent, the other black wire may be used. Do not use the green and white wires: these are meant for data transfer, so insulate them.

The basic cross section view of sterio jack and sterio socket are given below, incase if you dont know