This trimmer or reaper amplifier cuts the signal peaks at a voltage determined by the zener diodes. The gain is given by R1 and R1 and the power supply must be symmetrical from 5 to 15 V.
The circuit presented in the figure is an amplifier for stereo sources with the Maxim MAX9723...
In fact, this 1994 circuit uses a scale of LEDs to indicate the pulse rate applied to its input....
What differentiates this circuit from the previous one (CB15613E) is the non-need to use a...