Microphone

Dual-Channel Microphone Preamplifier (F4558)

This repository contains the design and documentation for a high-gain microphone preamplifier utilizing the F4558 Dual Operational Amplifier. The circuit is optimized for low-noise amplification of small-signal audio inputs.

⚡ Circuit Features

• Topology: Inverting Transimpedance Amplifier (TIA) configuration.
• Constant Gain: Fixed by a 470kΩ precision feedback resistor.
• Stability: Includes a 10pF compensation capacitor ($C_6/C_7$) in parallel with the feedback loop to prevent high-frequency oscillation and roll off ultrasonic noise.
• Biasing: Virtual ground established at +6V (half-supply) to allow for single-supply operation from a +12V source.
• Input Stage: AC-coupled via 4.7µF electrolytic capacitors with 10kΩ pull-ups for microphone biasing.

🖼 Schematic Overview

The design uses both halves of the F4558 (U1A and U1B) to provide dual-channel processing.

📂 Project Files

• mic-amp-report.pdf: Full engineering report, including frequency response curves and BOM.
• index.html: Project landing page.

🚀 Calculations

The gain for this specific inverting setup is defined by the input impedance of the microphone vs the feedback resistor ($R_f$):

$$V_{out} \approx -I_{in} \times R_f$$

The low-pass cutoff frequency ($f_c$) created by the feedback network is: $$f_c = \frac{1}{2\pi \times 470k\Omega \times 10pF} \approx 33.8 \text{ kHz}$$ This ensures the full audible spectrum is captured while filtering out unwanted RF interference.