Audio Preamplifier

This tiny board features a dedicated microphone and audio preamplifier from Analogue Devices. It is ideal for use in PA systems & transceivers to improve vocal clarity.

Supports Different Microphone Types
The design works well with dynamic, electret, crystal and ceramic microphones. Screened cable must be used to connect any type of microphone to the preamplifier. The input is unbalanced and probably not suitable, as it stands, for sensitive balanced feeders common with very high quality studio microphones. This design also has no provision for phantom power.

Automatic Gain Control (AGC) = Steady Output

A true RMS level detector samples the varying input and control circuitry sets a constant output level. This AGC response has been tailored for voice & music applications.

Built-in Level Meter Driver

The meter driver circuit is driven by the AGC section and provides good visual feedback of the signal level. This flexible circuit accepts a wide range of meter movements. The component value for 50uA, 100uA, 500uA & 1mA FSD movements is indicated.

Compression = More SSB Talk Power = More Range = More Contacts!

Compressing the microphone audio to a SSB transmitter increases the average talk power which can result in a 6dB increase in reported signal strength!

Frequency Response To Suit Your Needs.

The standard audio frequency response is 300Hz to 3kHz which is ideal for amateur radio applications. This can easily be expanded to 20Hz to 20kHz with the change of only 2 parts!

Radio Receiver Audio Preamplifier with AGC, Squelch & S-meter!

The board can be incorporated into radio receivers as an advanced audio derived AGC preamplifier. In this instance, it would be installed just after the product, diode or regenerative detector. In this application it will provide a constant audio level, squelch control and signal strength meter.

Noise Gate for Quiet Operation

To reduce background noise and hiss, an on board “squelch” control is very effective in eliminating output noise below the level of audibility.

Limiting To Prevent Overdrive

Very effective limiting is available to prevent the occasional transient from overloading the desired maximum output.

Wide Operating Voltage

The on-board L7805CV 5V regulator accepts 7V to 35V input. The regulator can be omitted if an existing 5V regulated supply is provided.

Easy to assemble.

All parts are through hole types only – no surface mount parts at all. Ideal for us old guys with poor eye sight!

Limited Production - Short Kit

This is a limited production short kit. It includes the circuit board and the Analogue Devices SSM2166 IC only. You need to provide easy to obtain parts and complete assembly. Most radio amateurs & electronics enthusiasts will have the required parts in stock. 


  • Input Voltage: 5V & 7V – 35V DC
  • Operating Voltage: 5V
  • Operating Current: 10-50mA
  • Gain: up to 60dB
  • Compression Range: 1:1 to 15:1
  • Input Level: 50uV to 20mV
  • Output Level: up to 1.4V RMS @ 1% THD
  • Frequency Response (default): 300Hz to 3kHz
  • Frequency Response (extended): less than 20Hz to greater than 20kHz
  • Supported Microphone Types: Dynamic, Electret, Crystal and Ceramic
  • Board Dimensions: 32mm x 68mm

Download SSM2166 Datasheet & project instructions below. 

IMPORTANT: Click on the Down Arrow to the right of the file name to download complete file.

Chris Day,
Mar 1, 2015, 7:45 PM
Chris Day,
Nov 18, 2013, 7:42 PM