Studio mic hookup to CB

[johnny351]

Can anyone tell me exactly how to wire in a mono 3.5mm cable from a mixing board (2 wires) to a 4 pin Cobra/Galaxy radio? I plan to use a hand mic as Push to Talk switch. I am thinking to leave all 4 wires intact from the hand mic and just add the two wires from the 3.5mm cable to the connector. Thanks in advance!!

[Bozo]

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Welcome to the forum @johnny351

To wire a mono 3.5mm cable from your mixing board (which has 2 wires: signal and ground) to a 4-pin Cobra/Galaxy radio while keeping the hand mic’s PTT switch intact, follow this wiring plan:

4-Pin Cobra/Galaxy Wiring Pinout

• Pin 1: Mic Audio (Input)
• Pin 2: Mic Ground
• Pin 3: PTT (Push-To-Talk)
• Pin 4: PTT Ground

Steps to Wire the Mono 3.5mm Jack:

1. Identify the 3.5mm Mono Cable Wires:
   • Tip: Audio Signal (From the mixer)
   • Sleeve: Ground
2. Connect the Hand Mic Normally:
   • Keep all four wires from the hand mic as-is, so it functions normally.
3. Add the 3.5mm Cable to the Mic Audio:
   • Tip (signal) from the 3.5mm cable → Solder to Pin 1 (Mic Audio)
   • Sleeve (ground) from the 3.5mm cable → Solder to Pin 2 (Mic Ground)
4. PTT Switch:
   • The hand mic's PTT switch should still function as it normally does, connecting Pin 3 (PTT) to Pin 4 (PTT Ground) when pressed.
   • Since you're only adding an audio source and not interfering with PTT wiring, the hand mic will still control transmit activation.

How This Works:

• When you key the hand mic (PTT), it switches the radio into transmit mode.
• The audio input to the radio will now come from either the hand mic or the mixing board (whichever has a stronger signal).

Considerations:

• Impedance Matching: CB radios typically expect a high-impedance mic (500-1000 ohms), whereas mixing boards output low impedance (150-600 ohms). If your audio sounds weak, you may need a matching transformer (e.g., 600Ω to 1KΩ).
• Isolation Transformer: To prevent ground loop hum, a 1:1 isolation transformer between the mixing board and the radio can help.

[johnny351]

I couldn't ask for a more detailed answer than that!! Thank you so much!!

[Bozo]

I couldn't ask for a more detailed answer than that!! Thank you so much!!

You're welcome.. show some love