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Re: Mic doesn't work in bitx40 #bitx40

Mike aka KC2WVB
 

If your still having trouble tomorrow, I'll wire my microphone jack/receptor and post a picture to this posting by Sunday afternoon.

Like I said before the little microphone has a JFet transistor in it. The pin out of the JFet called a 'gate' is attached to an internal aspect of the microphone that acts kind of like a plate in a capacitor. As you speak an internal outer plate vibrates and in doing so moves nearer then further from the part attached to the gate of the transistor and in doing so creates an ac current. The leg of the transistor called the 'source' is connected to the outside can of the microphone and must be connected to ground. One of the wires protruding from the bottom of the can is directly connected to this as well. The leg of transistor called the 'drain' is doing two things. It is providing dc voltage to the transistor from the power supply and since there must be a resistor prior to this leg it is also providing the path for the ac audio out that meanders to presumably a small op-amp or something similar.

If you mis-wired the microphone could you have damaged the microphone. It's hard to say without knowing the specifics. Transistors are like a diode and reversing the polarity could muck them up. If you know how to test a JFet transistor you could test your microphone. On the other hand they are very inexpensive and you can pick a new one up for under a dollar.

If you mis-wired the microphone could you have damaged the amplifier that the microphone feeds. Again it is hard to say. I've built little single stage amps with Bipolar Junction transistors, MOSFETs and integrated circuits such as the LM386 and in a confusion of wires around the breadboard I have reversed polarity without issue but I don't know enough to say that's not the case here. I hope not for you because it would be more difficult to fix from a mechanical point of view than replacing a burned up microphone.

Hope you resolve this issue.

Mike

On Fri, May 25, 2018, 9:20 PM Mike aka KC2WVB <rb5363@...> wrote:
One last thing that I should have mentioned. The heavy yellow wire in the picture of how I wired the volume potentiometer is the wire that comes from the positive side of the power supply to the switch feature on the potentiometer which is the bottom two pin outs on the potentiometer.

I used my own wire and all I had was yellow. I probably should have used red or brown which I think is what the kit uses but to me it did not matter other than I wanted a heavier gage wire than provided.

On May 25, 2018 9:11 PM, "Mike aka KC2WVB" <rb5363@...> wrote:
I thought you were having trouble with sound coming out of the headphone jack while in receive mode???

If you are having issue with sound on receive:

Here are two pictures. One is a picture of the volume potentiometer and how it should be wired on the BitX40. The other is a picture of the audio headphone jack and how it should be wired on the BitX40.

If your having issues on the Mic:

I have not yet installed my microphone jack but it should be fairly easy and it probably goes like this.?

One pin out connector on the jack/receptor brings in probably 5 volts dc and probably has a 2.2K resistor in line with the wire providing the voltage. Another pin out on the jack/receptor corresponds with the shank of the 1/8 inch stereo plug and it is grounded. The last connector carries the ac audio signal on a dc offset voltage to a capacitor where the dc is stripped away leaving just ac that then probably goes into an amplifier before it goes anywhere else.

There are good 10 minute videos on YouTube that show how these electrec microphones work and it would probably surprise you to here that there is a jfet transistor in the microphone case but there is so you want to wire this thing exactly as told and not to deviate at all or it will not work.

On Tue, May 22, 2018, 1:22 AM <qonita.salimah@...> wrote:

Thanks for your reply..

I've already swap the leads of the electret mic. But the same thing is happened. What voltage suppose the capacitor showed exactly?
is there any limitation on how big the voltage is to make the mic work?

thank you very much
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