Balance Controlled Microphone Preamplifier Circuit (+3 Band Equaliser)

The circuit is fed with 9 volt batteries based on 2 tl072 op-amps. If desired, it can be used with a 15 volt DC Adapter on the DC rectification and regulated circuit. I recommend using a battery for low noise. The circuit does not draw much current.

Balanced Microphone Preamp Circuit

The rugged design includes a 3-band equalizer. It also has balanced and unbalanced outputs and can drive a stereo or guitar amplifier.

Microphone Preamp Circuit Main Features

Balanced input for microphone
Balanced and unbalanced output
Level control
3-band equalizer
battery indicator

The circuit is based on two low cost op amp ICs: TL072 IC1a and IC2. The IC1a functions as an unbalanced preamplifier while the IC1b functions as a 46-gain non-inverting amplifier. IC2b provides the out-of-phase signal for pin 3, while IC2a, VR2, VR3, and VR4 make up the equalizer stage.

Whether for karaoke, public concert or a band, a microphone connection to an amplifier is a basic requirement. This Balanced Microphone Preamplifier includes a 3-band equalizer and can be used to drive a guitar amplifier, any stereo amplifier, or to provide an additional channel for a public address amplifier.

Balanced microphones are preferred because they prevent the spread of sound and noise into the sound system. A balanced microphone usually has a 3-wire cable that connects with XLR plugs and sockets.

XLR pin 1 is return or ground and the other two terminals (pins 2 and 3) are for signals. The signals are in anti-phase; In other words, when one row is positive, the other row oscillates the same amount of negative. Any hum collected along the cable is effectively canceled because the same level of hum is present on both signal lines.

XLR microphone preamp circuit diagram

Microphone Preamplifier of EQ

Source: http://www.siliconchip.com.au/cms/A_102159/article.html

Microphone Preamplifier PCB schematic alternative link: