MAX9814 Microphone Amplifier AGC Auto Gain Control

Description

Add an ear to your project with this well-designed electret microphone amplifier with AGC. This fully assembled and tested board comes with a 20-20KHz electret microphone soldered on. For the amplification, we use the Maxim MAX9814, a specialty chip that is designed for amplifying electret microphones in situations where the loudness of the audio isn’t predictable.

This fancy microphone amplifier module is a step above the rest, with built in automatic gain control. The AGC in the amplifier means that nearby ‘loud’ sounds will be quieted so they don’t overwhelm & ‘clip’ the amplifier, and even quiet, far-away sounds will be amplified. This amplifier is great for when you want to record or detect audio in a setting where levels change and you don’t want to have to tweak the amplifier gain all the time.

The chip at the heart of this amp is the MAX9814, and has a few options you can configure with the breakout. The default ‘max gain’ is 60dB, but can be set to 40dB or 50dB by jumpering the Gain pin to VCC or ground. You can also change the Attack/Release ratio, from the default 1:4000 to 1:2000 or 1:500. The ouput from the amp is about 2Vpp max on a 1.25V DC bias, so it can be easily used with any Analog/Digital converter that is up to 3.3V input. If you want to pipe it into a Line Input, just use a 1-100uF blocking capacitor in series (100uF sounds best).

We are using this board for Speech Recognition, feeding the output directly to ADC input of ARM Controller for processing.

Applications

• Speech Recognition
• Bluetooth Headsets
• Two-Way Communicators
• High-Quality Portable Recorders
• IP Phones/Telephone Conferencing

Technical Specifications

• Supply Voltage: 2.7v-5.5v @ 3mA current
• Output: 2Vpp on 1.25V bias
• Frequency Response: 20Hz – 20 KHz
• Programmable Attack and Release Ratio
• Automatic gain, selectable max from 40dB, 50dB or 60dB
• Low Input-Referred Noise Density of 30nV/
• Low THD: 0.04% (typ)

Module Schematic