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DIY Audio FET Switch

Though you can route audio through a traditional switch or relay directly, the metal contacts in the switch put unwanted electrical noise in the signal. By using a field-effect transistor, you avoid this noise. Here, a switch does not carry audio; the switch controls a transistor that carries the signal. Because the FET has no moving parts, it produces no objectionable pops or clicks when you switch it on. The FET, being a voltage-based device, draws very little current; an inexpensive 9-volt battery provides plenty of power for the circuit.

Things You'll Need

Solderless breadboard
2N3819 field effect transistor
2, 4.7-microfarad, 16-volt capacitors
47-nanofarad, 16-volt capacitor
3, 47K-ohm, 1/4-watt resistors
1M-ohm, 1/4-watt resistor
50K-ohm, 1/4-watt resistor
100-nanofarad, 16-volt capacitor
Single-pole, single-throw switch, breadboard type
4, 8-inch pieces of 22-guage connecting wire
Labeling tape and pen
9-volt battery clip
9-volt battery

Instructions

Install Components Into Breadboard
- 1
  Insert the FET into the breadboard so each of its leads go into separate columns on the board. Each socket in a column is electrically connected to the others; adjacent columns are electrically isolated from one another.
- 2
  Insert the positive lead of one of the 4.7-microfarad capacitors so it connects to the FET̵7;s drain lead. Insert the capacitor̵7;s free lead into an unused column in the breadboard.
- 3
  Set one end of a 47-nanofarad capacitor to connect to the FET̵7;s gate lead. Insert the capacitor̵7;s free lead into an unused column.
- 4
  Insert one lead of a 47K-ohm resistor into the column that has the 47-nanofarad capacitor̵7;s second lead. Insert the resistor̵7;s second lead to connect to the 4.7-microfarad capacitor̵7;s positive lead.
- 5
  Set one lead of the 1M-ohm resistor so it connects to the FET̵7;s gate lead. Put its other lead into an unused column.
- 6
  Insert one lead of the second 47K-ohm resistor so it connects to the column containing the second 1M-ohm resistor lead. Insert the other end so it shares the column connecting the first 47K-ohm resistor and the 47-nanofarad capacitor. This column is the circuit's ground connection.
- 7
  Set one terminal of the switch into the column connecting the 1M-ohm and 47K-ohm resistors. Set its other terminal into a free column.
- 8
  Insert one lead of the third 47K-ohm resistor so it connects to the FET̵7;s source lead. Connect the other lead to the ground column.
- 9
  Connect the positive lead of a second 4.7-microfarad capacitor to the FET̵7;s source lead. Set the other lead into a free column.
- 10
  Insert one lead of the 50K-ohm resistor into the column that has only the second lead of the second 4.7-microfarad capacitor. Insert its other lead to the circuit ground column.
- 11
  Connect one lead of the 100-nanofarad capacitor to the ground column. Set its other lead into the column that has only the switch terminal.
Input Wiring
- 12
  Insert one end of a 22-gauge wire into the circuit ground column.
- 13
  Insert one end of another 22-gauge wire so it connects to the column shared by the 50K-ohm resistor and 4.7-microfarad capacitor.
- 14
  Twist the two wires one turn around each other and label the pair ̶0;Input.̶1;
Output Wiring
- 15
  Insert one end of a third 22-gauge wire to the ground column.
- 16
  Set one end of a fourth 22-gauge wire so it shares the column which has only one lead of the first 4.7-microfarad capacitor.
- 17
  Twist this wire one turn around the third wire and label the pair ̶0;Output.̶1;
Connect The Battery
- 18
  Insert the negative lead of the battery clip to the column that contains only the 47K-ohm resistor lead.
- 19
  Connect the positive lead to the circuit ground column.
- 20
  Snap a 9-volt battery into the clip.

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