How to Wire a K40 Mic

Written by simon foden Google
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How to Wire a K40 Mic
The K40 micophone is typically marketed towards truckers. (Thinkstock/Comstock/Getty Images)

The K40 is a noise-cancelling, omnidirectional microphone typically used in citizen's band, or "CB" radio communications. The microphone is ruggedly constructed with a wire mesh grille to protect the interior components. It has a 9 foot cord which connects to the CB transmitter. This microphone is marketed chiefly to drivers who use CB radio communications. For optimum performance and safety, it is essential that the K40 microphone is correctly wired to the CB transceiver rig. The microphones come partially assembled so that you can wire them according to the requirements of your rig.

Skill level:

Things you need

  • Ohmmeter
  • Soldering iron
  • Solder
  • Jeweller's screwdriver
  • Phillips screwdriver
  • Wire cutters

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  1. 1

    Determine which switching system your transceiver uses. This is important because the switching system of the transceiver determines the wiring configuration of the microphone. There are two main types of transceiver switching systems: electronic switching and relay switching. There are two types of relay switching, both are similar and call for the same configuration: direct relay switching and transistor driven relay switching. Turn the transceiver off. Connect one Ohmmeter lead to the negative, direct current input lead on the transceiver. Connect the second ohmmeter lead to the transceiver ground pin. Turn on the Ohmmeter and write down the resistance that it records. If the resistance is greater than 2000 Ohms, this indicates that the CB transceiver uses the electrical switching method. Anything less than 2000 Ohms indicates relay switching.

  2. 2

    Remove the grille from the front of the microphone. Solder an "R2" resistor to the top side of the printed circuit board inside the mic. Use a 25-watt soldering iron. Solder the resistors and diodes that come with the mic to the printed circuit board. The printed circuit board is pre-drilled, which means that only the correct part fits in the turret, meaning that you will not be able to fit a diode where a resistor should be. Consult the wiring schematic to ensure that you are installing the correct resistor. Resistors are colour-coded according to their value. The capacitors act as radio frequency filters.

  3. 3

    Adjust the microphone output level switch located on the rear of the circuit board with a jeweller's screwdriver. Screw the circuit board into the microphone chassis.

  4. 4

    Solder the K40 speech processor output terminal to the input of the transceiver using the white lead supplied with the microphone. Solder the supplied blue lead to the microphone connector pins on the transceiver.

  5. 5

    Connect the yellow lead supplied to the ground pin on the transceiver. Strip a small piece of the insulation from the loose end of the wire and wrap the bare metal around the same ground pin that you used to measure the microphone resistance. You only need to ground the yellow wire if you determined that your transceiver uses the electric switching method.

Tips and warnings

  • Set your Ohmmeter to "resistance" before turning it on.
  • Transceiver rigs can carry potentially lethal voltages if not handled with care. If you are unsure, consult a professional electrician.

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