Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 94

Circuit 71: low-noise preamplifier
Setup information
Install the two transistors, the three resistors and the two electrolytic capacitors as shown in Fig. 2.71. The
six 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 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
You should choose a pickup of high quality to play your vinyl records. The premier class includes the
"moving-coil" pickups. Unfortunately these have very low output voltage. We need to connect a low-noise
preamplifier before the RIAA equalizer amplifier. We will connect two transistors in parallel; this reduces the
inevitable amplifier noise by half. Connect the "moving-coil" pickup to the input.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.71.
96
Components required:
2 x 2N3904 transistors,
1 x 470 kΩ resistor,
1 x 100 Ω resistor,
1 x 1 kΩ resistor, 1 x 100 μF
electrolytic capacitor,
1 x10 μF electrolytic capaci-
tor, 1 x Piezo element,
1 x breadboard, 1 x 9V bat-
tery with clip connector
Fig. 2.71: Low-noise preamplifier