This is a 1960s amplifier setup found in a period publication. The circuit uses a special driver transformer that inverts the phases of the signal to excite the output transistors.
Found in the March 1974 Radio Electronics magazine, this circuit is designed to measure the level...
Adafruit Breakout PDM Microphone This Adafruit tested microphone card is available from Mouser...
This circuit was obtained from a 90s Radio Electronics. The value of R1 determines the scale...