A simple amplifier designed to take a signal from a microphone/instrument. Gain is ~1200 (60 dB).
The circuit has two switches on the far left The top most switch will route the input signal to both inputs of the op-amp (common mode), with the switch off it is set in differential mode.
The bottom switch chooses which input to use on the op amp.
This is an audio amplifier, specifications are as follows:
1. Gain of 1228 (~61.7 dB)
2. CMMR of 50 dB between 40Hz and 20kHz
3. Input impedance between 1-10k (with one input grounded)
4. Frequency Response within +- 0.5 dB from 40Hz to 20kHz.
The major problem in the design here is getting the correct gain for the non inverting input on the first stage, while keeping the input impedances in the correct range. The 2k resistor on top left most corner is the major factor here, too high and you lose gain, too low and you lose input impedance.
The second stage is just a simple non inverting amplifier that has a switch that drops the signal by -20 dBu.
