06/01/2014 - 07/01/2014 ~ ALL

3 Input Mic Mixer Circuit

Here is a simple 3 input mic mixer circuit using the popular uA 741 ICs. Four 741s are used here.IC1, IC2, IC3 are used as preamplifiers. They produce a gain of around 40 decibel to the individual input signals. The IC4 is wired as a summing amplifier to add the signals from three preamplifiers.IC4 also gives a gain of around 5decibel to the final output signal. Total gain of the system is around 45decibel.

Notes.

Assemble the circuit on a good quality PCB.
A +15/-15 V DC dual power supply is needed for powering the circuit.
All inputs and output must be connected with respect to the ground.
ICs must be mounted on holders.
Electrolytic capacitors C1, C2 and C3 must be rated 10V and other capacitors must be 30V.

Musical Bell (UM 66)

This circuits uses very few component and gives melody sound. It uses 3 terminal IC UM66 and can be build small enough to be placed inside a greeting card and operated off a single 3V flat button cell.

There is not much to the circuit. The UM66 is connected to its supply and its output fed to a transistor for amplification. Any common speaker can be used or a “flat” piezoelectric tweeter like the one found in alarm wrist watches. If you use the piezo, then it can be connected directly between the output pin 1 and ground pin 3 without the transistor.

The UM66 looks like a transistor with 3 terminals. It is complete miniature tone generator with a tune. Now they come with wide variety of different tunes.

For amplification we have used a NPN transistor which is BC548. Here BC548 makes a common emitter circuit. For limiting the base current we have used a resistance of 220 Ohms so that transistor will not get damaged by excess current.