6-Channel Audio Mixer
This audio mixer provides six input channels, combining 3 microphone inputs and 3 line inputs. It is designed using operational amplifiers for precise mixing and gain control.
Microphone Inputs
- Supports dynamic microphones with low impedance (200–100 Ω).
- For ECM (electret condenser) microphones, a series resistor must be added in the input line.
- Internal amplifier provides a fixed gain of 2 (≈6 dB) for mic channels.
Line Inputs
- Three line-level inputs with higher input impedance.
- Line inputs have a gain of 40 dB to match signal levels with microphone channels.
Circuit Operation
Each input channel is amplified by an op-amp stage, allowing proper summing and mixing of all signals. Individual volume control for each channel can be added for independent adjustment. The mixed output can then be sent to a recording device, amplifier, or speaker system.
Key Features
- 6 channels: 3 microphone + 3 line inputs
- Supports dynamic and ECM microphones
- Internal mic gain: 6 dB (×2)
- Line input gain: 40 dB
- Op-amp based design for low noise and high fidelity
- Compact and versatile for small audio setups
Construction Notes
- Use low-noise op-amps for high audio quality.
- Keep microphone input wiring short and shielded to prevent interference.
- For ECM microphones, include the series resistor as specified to provide proper biasing.
- Include decoupling capacitors near the op-amps to minimize noise and oscillations.
- Volume potentiometers can be added per channel for independent level control.
