Hi everyone!
I've made a "Telephone Microphone" that is fairly simple to make, just use the two wires from the earpiece of the phone and solder them to a guitar jack and thats it. The thing is that I tried to add a lowpass filter with a 100K potentiometer and its correspondant capacitor (to roll of a bit of the highend freq. so it doesn't feedback, and the problem is that when I turn down the pot, it stats to hum. I've tried different wirings, use shielded wire, and NOTHING.
So, then I tought it was a good idea to get rid of the pot and use a ON/ON switch and add the RC filter to it so you can select between the "normal" telephone sound signal or the filtered signal. Aaaaand it didn't work. I'm using a 3.5K resistor with a 0.047mF capacitor, wich in theory will result in a cuttoff freq of 900Hz, more than enough to me, but it doesn't affect the signal at all! When I use the potentiometer, I added a 47pF capacitor and it works, but, as I said above, IT HUMS. I tried to solder the resistor and capacitor directly to the jack and, nothing...
The earpiece has a very low reading, a 20 ohm, so maybe that causes the problem or I don't know. I've seen other people add a volume or filter pots to this phones and they just work fine! (of course I've ask them but got no answer back) I also tried on 3 different phones and the result is the same.
Also, I must tell you that I'm very new at this and I still don't know how to read schemantis propperly, so be pacient please haha.
Anyways, hope you can help!
Thank you!
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Topic: Telephone Microphone Circuit Bent POTENTIOMETER HUMMING (Read 3888 times)