Ham Radio Microphone Selector Switch. In some Ham Radio Shack there are more microphones than transceivers. But when broadcasting there is only one mouth and one radio, so a microphone is sufficient.
However, when we find a strange mic or a classic mic, we buy it on impulse.
The sound depends on the taste of the listener. You would like to compare which one sounds better, the standard attached microphone or the new microphone you have purchased.
We are going to make a microphone selector. You don’t need the annoying work of unplugging the mic connector and replacing it with another mic, asking How about this mic? The change is possible simply by turning the rotary switch 1, 2 and 3.
Ham Radio Microphone Selector Switch with IC NJM2750
This IC is a 4-in, 1-out stereo audio selector. Since it has 4 inputs, 4 types of microphones can be connected to this selector and switched with a rotary switch.
The IC supports stereo signals, but since it is used for radios, we only use one channel.
NJM2750 cannot be directly attached to a 2.54mm pitch universal plate, which is often used in normal production. So we assemble it using a DMP16 and the universal board conversion board.
Ham Radio Microphone Selector Switch Circuit diagram
The circuit diagram is based on what was listed as application circuit in the datasheet. This IC has 4 inputs and 1 output, but since there was not enough space in the aluminum housing used, it was inevitable to use 3 input microphone connectors. If there is enough space in the box to be installed, 4 circuits can be provided.
Let’s do it
The power supply is powered by 6V with 4 AAA batteries. According to the datasheet, the operating voltage of the IC used is 4.7-13V, which is a sufficient range, so 6V is fine.
We do not use AC power supply to avoid circuit noise on the microphone line.
Looking at the IC datasheet, the circuit is straightforward. SW1 and SW2 generate four types of two-bit control signals. This 2-bit signal switches the input between 4 inputs inside the IC.
The input can be switched by inputting a 2-bit control signal to pin 2 and pin 4 of the IC. Since the control circuit does not need to be assembled with logic, H and L are made by connecting H to 6V and L to GND level as shown in the circuit diagram.
6V is applied to the microphone line through the 10kΩ resistors of R4, R5 and R6. This is because a condenser microphone is used, which is not necessary if you are using a dynamic microphone. If you install an ON OFF switch of this resistor inside, it can drive any type of microphone.
Put the circuit in an aluminum box to make it look nice. You can also install an LED on each microphone connector on the front panel so you can see which microphone is connected.
4 Input 1 Output STEREO Audio Selector
- Operating Voltage (4.7to13V)
- 4 Input / 1 Output Audio Selectors
- Dual Channel for Stereo Use
- Low Output Noise (-110dBV typ.)
- Low Distortion (0.005% typ.)
- Bipolar Technology
- Package Outline (DMP16)
The NJM2750 is 4 Input / 1 Output Stereo Audio Selector. Based on the internal Switch OP-AMP technology, the NJM2750 has lower Output Noise, lower Distortion and higher Channel Separation than the ordinary Multiplexers or Analogue Switches. The NJM2750 is suitable for any kinds of audio equipments, such as TV, Car Stereo, Mini-Compo and so on.