K2 microphone jack grounding
17 Nov 1999
We recently discovered that we had left out the assembly step in which the microphone jack is grounded to the front panel. This will NOT affect the way the mic or the K2 works. Some mics, in fact, ground the shield internally at the mic plug, so grounding the mic jack itself would be optional. (It seems the majority of current HF rig mics do not use ground the shell..)
For Mics that do use the shell as a ground return path, grounding the jack may reduce pickup of stray RF. This is important if you use end-fed or poorly-matched antennas, or have a minimal ground system. You should definitely ground the mic jack if you suspect any RF problem or if you anticipate field operation with end-fed wire antennas.
GROUNDING THE MIC JACK
The simple mic jack grounding method described here has been carefully tested and is reliable, but we plan to modify the front panel board to make it easier in the future.
NOTE: It is NOT necessary to disassemble the front panel from its PC board during this procedure.
1. Remove the two screws that hold the front panel to the control board, and the four screws that hold the front panel assembly to the chassis. Separate the front panel assembly from the chassis.
(Alternatively, just remove the left side panel of the
2. Remove the insulation from about 6 inches of #22 or #24 solid hookup wire.
3. Loop this bare wire around the threaded part of the mic jack (between the PC board and the aluminum panel). This operation is facilitated by the square hole in the PC board near the mic jack: after inserting the wire from the side of the panel, it can be grabbed through the square hole using long-nose pliers, then routed back around the other side of the jack.
4. Once a loop is formed around the jack and both ends are accessible at the side of the panel, twist the wires tightly together close to the jack so that the loop cannot slip. Leave at least 2" of wire free at one end. Then solder the twisted wires together right at the jack.
5. Connect the free end of the mic jack ground wire to the short ground jumper that is located along the nearby edge of the front panel board. Solder the mic ground wire to the ground jumper.
6. Clip any excess wire. Re-attach the front panel assembly to the K2 chassis.
7. Plug in the mic and measure the resistance from the mic plug to the K2's chassis ground. It should be very low (< 10 ohm).
©1999, Elecraft LLC