Low-Noise High-Impedance Input Amplifier - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.61 Low-noise high-impedance input amplifier

Circuit 132: High-impedance preamplifier
Setup information
Install the two transistors, the eight resistors, the ceramic capacitor and the electrolytic capacitor as shown
in Fig. 2.132 The nine jumper wires come next. Last but not least, connect the Piezo element. Check the
placement on the board again and only then connect the battery. You can significantly increase the sensitiv-
ity of the Piezo element by using a sound plate or even a sound box. Read more about it in Chap. 1.2.3
Experiment
Even if everything is wired correctly, you won't hear anything at first. If you connect an mp3 player to the
input, loud music will come from the Piezo element, even though you have turned the volume very low. The
input is very high impedance, and when you just touch it with your bare finger you will hear some scraping
and humming sounds .
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.132.
Components required:
1 x 2N3906 transistor,
1 x J111 FET transistor,
1 x 1 MΩ resistor,
1 x 22 kΩ resistor,
1 x 10 kΩ resistor,
3 x 2.2 kΩ resistor,
1 x 1 kΩ resistor, 1 x 100 nF
ceramic capacitor,
1 x 10 μF electrolytic
capacitor, 1 x Piezo ele-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.132: High-impedance
preamplifier
157