Microphone Amplifier

My wife does an occasional quiz and needed a microphone amplifier. As the quiz includes music questions, a music input was also needed.

I bought via eBay and assembled a 15+15 Watt RMS audio amplifier that uses TDA2030 I.C.s. Also a switch mode power supply unit that provided a 24 volt DC supply, which I adjusted down to 20 volts to match the amplifier power requirements.

Next I decided to build a suitable preamplifier. I sketched out a circuit that uses NE5532 op-amps.

I built this on a breadboard block for testing. It has a balanced input for the microphone. The fourth op-amp is unused and this could be used for a second microphone input, if required. (Unmarked capacitors are 100nF but weren't required.)

Having finalised the circuit and component values, I transferred the components to perforated copper stripboard.

A diecast box was used as a fully-screened housing. I drilled and filed holes for the plastic support pillars, XLR microphone socket, DC supply socket, Loudspeaker sockets, Stereo 1/4" jack socket and telltale LED.

I mounted a pair of loudspeakers to a 1/2" plywood baffle with foam and expanded steel to protect the speaker cones.

Finally, I constructed a box from 1/2" plywood and filled it with pillow stuffing to reduce resonance.

The final unit is not "High Fidelity" and you can produce very obvious distortion if you turn the volume too high. However, with a total output of 30 Watts RMS, it is perfectly adequate for a quiz night or karaoke with a small group of people.

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