This simple 1-transistor audio preamplifier appeared in the June 1968 Radio Electronics magazine. The transistor is a general-purpose type of the time. The gain is 14 dB.
In fact, this 1994 circuit uses a scale of LEDs to indicate the pulse rate applied to its input....
We found this circuit, which is actually a window discriminator, in the 1991 Electronics...
This circuit acts on the dynamic range of an audio signal, which can be useful for recording,...