Often times we used a simple toggle switch to switch between audio source. This is the easiest and simpliest method. But this simple circuit creates some clicking or boom sound when switching audio sources specially when the 2 audio source are operating. Here’s a simple and effective circuit to switch between audio sources gently. It gently decrease the volume of the audio source previously selected and while slowly increasing the volume of the selected audio source.
About the circuit:
The circuit is not that complicated. It uses CD4016 bilateral switch ic (U1) for switching the signal. R1 and C1 is used to slow down the switch enable voltage being fed to the switch ic. This 2 components control the fade time. You can increase the fade time by increasing the value of any of the 2. R3 and C2 works the same way as R1 and C1, it is only used for the other channel. U2 is only a buffer gate IC and you can use any type except for an open drain output type. R2 and R4 is only used for terminating the input of the buffer so it will be terminated to ground when the input is left open. This is likely to happen if you will use 1 pole selector switch.