Most audio signal sources only have one stereo output, which means they can only drive a single pair of headphones with a resistance of about 32 ohms or a single line with a resistance of 600 ohms. But sometimes, like for entertainment, e- learning and training, or at home, more than one person needs to connect their headphones to the same sound source. When these things happen, it's not a good idea to use loudspeakers because they will bother other people in the room. Also, sometimes the signal from one audio output needs to be sent to several power amplifiers that are many meters apart. In this case, the distribution device should be

able to drive long audio lines with resistance between 100 and 600 ohms. A distribution buffer (DB) is added between the audio output and the headphones to meet this kind of need. Most headphones have a way to change the volume. So, to keep things simple, there is no volume control added to the distribution buffer. Circuit and working Figure shows the circuit of the stereo distribution buffer, which was built to solve practical problems that come up when the signal from a single stereo source needs to be buffered so that it can drive up to four headphones or small high-impedance loudspeakers with resistances higher than 32 ohms. The circuit has two channels that are the same. The buffer has one input for each channel and four outputs for each channel. The stereo signal comes in through CON1 connector. Connector CON2 has the same signal, so the second distribution buffer can be hooked up to that connector. R1 and R2 are input protection resistors with values that are usually between 100 ohms and 2 kilo-ohms. Their exact value depends on the signal source, the cables, the inputs, and other factors. The DC input component is cut with C1 and C2. Most of the time, the amplifier won't work right if DC voltage from the source is present. Also, C1 and C2 work as high-pass filters with the input resistance and should be calculated as follows: F3dB = 1/(6.28RinputC) The input resistance is 1 megaohm, and it mostly depends on what R5 and R6 are set to. Each channel has a gain of 1. Also, there are no potentiometers for controlling the volume because this keeps the circuit simple. When S2 is closed, both inputs come in at the same time. Connectors CON3, CON4, CON5, and CON6 all have outputs that can be used for headphones or audio interfaces. The outputs can be used in any way that makes sense. The buffer can send out a maximum total current of about 100 mA. The buffer is made up of a dual operational amplifier (IC1) and a few other discrete parts. Other operational amplifiers like the RC4560, OPA2132, TL072, TL082, and even the LM358 can be used. However, for audio, it is best to use amplifiers that can drive loads of 600 ohms or less and have a high input impedance. Depending on the operational amplifier that is used, the buffer can work with a wide range of power sources. When low-voltage rail-to-rail operational amplifiers are used,

a 5V USB power supply can be used to power the buffer. The circuit will also work with 5V/12V DC wall adapters that provide at least 200mA of current.