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DIY: Audio Preamplifier

A preamplifier takes a low-level audio signal and prepares it for amplification. By taking a low-volume signal and changing it to a line- or mic-level signal, the preamplifier conditions the sound for final amplification. The benefits of a preamplifier are improved sound quality and more efficient use of power. The more amplification applied to a signal in the final stage before speakers, the more noise introduced. Thus, the speakers need to use more power. Such amplification can result in speaker damage. A preamplifier reduces risk of speaker blowout and improves audio quality.

Things You'll Need

  • Blank circuit board
  • Copper tape
  • One 10 Meg Ohm Resistor
  • One 5K Resistor
  • Two 1K Resistors
  • One 30 ohm resistor
  • One transistor model number 2N2222A
  • One transistor model number 2N5484
  • One transistor model number 2N5087
  • One 1000uf capacitor
  • Jumper wires
  • 25-watt soldering iron
  • Rosin-core solder
  • 9V battery cap
  • Two standard audio pins
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Instructions

    • 1

      Add a small length of copper tape to your blank circuit board for use as a grounding strip and arrange the transistors and capacitor on blank circuit board by slotting each through the prefabricated holes. Orient the three transistors in a triangle in the center of the board with the 2N5087 transistor forming the peak, the N5484 forming the left corner and the 2N2222A transistor forming the right. Place the 1000uf capacitor beneath the N5484 transistor, leaving room for a resistor in between.

    • 2

      Place the 5K resistor to the upper left of the transistor triangle and the 10 megohm resistor to the lower left. Place the 1K resistor beneath the base of the transistor pyramid and the 30 ohm and other 1K resistors parallel and beneath the N5484 and 2N2222A transistors respectively. Orient all resistors with the brown band facing down.

    • 3

      Solder the components of your preamplifier into place with a 25-watt soldering iron. On the side of the board showing the bent connection pins, place a small amount of rosin core solder against the bent joint of the pin and the board. Touch the heated tip of your 25-watt soldering iron to the solder and melt a small amount of the solder directly to the board.

    • 4

      Begin wiring the resistors on your circuit board by using jumper wires. Wire the 5K resistor's top pin to your 9V Battery Cap and the 2N5087 transistor's collector pin. Wire the 5K resistor's bottom pin to the 2N5087 transistor's base and the 2N5484 transistor's collector. Wire the 10 megohm resistor's top pin to the 2N5484 transistor's base and the 10 megohm resistor's bottom pin to the ground. Wire the top pin of the 1k resistor placed between the 2N5484 and 2N2222A transistors to the base of the 2N5484 base and the top pin of the 30 ohm resistor and the 1K resistor's bottom pin to the 2N2222A transistor's emitter and the top pin of the other 1K resistor. Ground the second 1K resistor and wire the bottom pin of the 30 ohm resistor to the capacitor.

    • 5

      Wire the transistors, capacitors and create input and output feeds with jumper wires. Wire the emitter of the 2N5087 transistor to the the base of the 2N2222A transistor. Ground the unused connecting pin of the capacitor. Use jumper wires to create an audio input by connecting a standard audio pin between the 10 megohm resistor and the 2N5484 resistor. Use jumper wires to create an audio output by connecting a standard audio pin between both the 1K resistors and the 2N2222A resistor.

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