Overview

The MAX4466 is a ultra-low power, low-noise operational amplifier specifically optimized for electret condenser microphone (ECM) amplification, manufactured by Maxim Integrated (now Analog Devices). Mounted on a small 3-pin breakout module with a $20\text{ Hz to }20\text{ kHz}$ electret microphone capsule and a multi-turn trimmer potentiometer, it converts acoustic sound pressure waves into an analog audio voltage waveform.

Featuring an industry-leading Power Supply Rejection Ratio (PSRR of 112 dB), the MAX4466 effectively suppresses power supply ripple and digital switching noise generated by microcontroller power rails. Its single-ended analog output pin (OUT) produces an AC audio waveform centered at $\frac{V_{CC}}{2}$ ($1.65\text{V}$ at 3.3V supply), making it ideal for microcontroller sound level meters, FFT audio spectrum visualizers, and voice reactivity projects.

Quick reference

Pinout

Standard 3-pin 0.1" (2.54 mm) header:

Specifications

Gain Adjustment & Audio Waveform Math

The gain is set by a multi-turn trimmer potentiometer on the back of the breakout module:

• Full Counter-Clockwise: Minimum gain ($\approx 25\times$). Use for loud environments or close-range speaking.
• Full Clockwise: Maximum gain ($\approx 125\times$). Use for quiet ambient sound or soft whispering.

The OUT signal oscillates above and below the DC bias voltage ($1.65\text{V}$ at 3.3V supply):

$v_{audio}(t) = \frac{V_{CC}}{2} + A_{gain} \times v_{mic}(t)$

Peak-to-peak sound amplitude $V_{pp}$ can be computed by sampling the ADC over a $50\text{ ms}$ window (2 full cycles of a $40\text{ Hz}$ sound wave):

$V_{pp} = V_{max} - V_{min}$

Wiring

Example (Peak-to-Peak Sound Level Detector)

const int sampleWindow = 50; // Sample window width in mS (50 mS = 20Hz)
unsigned int sample;

void setup() {
  Serial.begin(9600);
}

void loop() {
  unsigned long startMillis = millis();
  unsigned int peakToPeak = 0;

  unsigned int signalMax = 0;
  unsigned int signalMin = 1024;

  // Collect data for 50 ms
  while (millis() - startMillis < sampleWindow) {
    sample = analogRead(A0);
    if (sample < 1024) {
      if (sample > signalMax) {
        signalMax = sample; // Save max level
      }
      if (sample < signalMin) {
        signalMin = sample; // Save min level
      }
    }
  }

  peakToPeak = signalMax - signalMin; // max - min = peak-to-peak amplitude
  float volts = (peakToPeak * 3.3) / 1024.0; // Convert to volts

  Serial.print("Sound Amplitude Volts: ");
  Serial.println(volts);

  delay(100);
}

Common mistakes

• Expecting line-level / headphone-level output to drive speakers directly: The MAX4466 outputs a low-power analog voltage signal meant for microcontroller ADCs or pre-amplifiers; it cannot drive $8\ \Omega$ speakers directly.
• Sampling too slowly for audio processing: Nyquist sampling requires taking ADC samples at $\ge 2\times$ the target frequency (e.g. $16\text{ kHz}$ sampling rate for $8\text{ kHz}$ audio bandwidth). Use DMA or fast ADC interrupts for FFT spectrum analysis.

Notes

• MAX4466 vs MAX9814: MAX4466 features manual gain adjustment via potentiometer; MAX9814 includes Automatic Gain Control (AGC) to equalize soft and loud sounds automatically.