Symmetric Nf Limiter - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.23 Symmetric NF Limiter

Circuit 56: Audio limiter
Setup information
Install the two transistors and the six resistors as shown in Fig. 2.56. Next install the three electrolytic
capacitors followed by the nine jumper wires. Finally connect the Piezo element. Check the placement on
the board again and only then connect the battery.
You can significantly increase the sensitivity of the Piezo element by using a sound plate or even a sound
box. Read more about it in Chap. 1.2.3
Experiment
This circuit limits audio signals. Microphones are usually connected at the input. If you are considering for
example nature recordings, a noisy background will quickly spoil your audio recording. A limiter is used to
avoid this. Loud audio signals are simply but inexorably symmetrically limited; in our case that is, any signal
at the input from 100 mV onwards; at the output to 500 mV. Weaker input signals are amplified normally.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.56.
Components required:
2 x 2N3904 transistors,
3 x 10 kΩ resistors,
1 x 22 kΩ resistor,
1 x 100 kΩ resistor,
1 x 1 μF electrolytic
capacitor, 2 x 10 μF
electrolytic capacitors,
1 x Piezo element,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.56: Audio limiter
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