Electronics > Beginners
Pre-amp to connect microphone to speakers
Audioguru:
--- Quote from: SoundFan on November 28, 2018, 09:31:24 am ---I've tried different mics and they work fine if connected directly to the PC. They are unpolarized but I have tried them in both directions already. The "squeaker" (I like that name) might be fried but the headphones work well.
--- End quote ---
You did not read about the LM386 gain and did not read about the electret mic that is definitely polarized. It will produce no output if it is connected backwards. Its metal case is connected to its "ground" pin (if it has only 2 pins) and the Jfet inside needs a positive current.
Why do you have such a tiny low power speaker? Headphones are tiny low power speakers.
SoundFan:
--- Quote from: Audioguru on November 28, 2018, 01:49:02 pm ---You did not read about the LM386 gain and did not read about the electret mic that is definitely polarized. It will produce no output if it is connected backwards. Its metal case is connected to its "ground" pin (if it has only 2 pins) and the Jfet inside needs a positive current.
Why do you have such a tiny low power speaker? Headphones are tiny low power speakers.
--- End quote ---
I do not really understand the purpose of your comment.
I have read about the LM386 gain but must have mixed up that "fixed gain" part with another IC. I have read about so many op-amps in the last few weeks to try to find one that works for my project and I am quite busy with my medical studies, so it isn't surprising that I mix up some stuff. Where do you think did I get the number 20 ( which is correct if there is nothing connected to pins 1 and 8 ) from ?
If the mic is polarized, how comes it has no marking on the pins to differentiate between the Gnd pin and the Vcc/Output pin ? And how comes it works on my PC and the LM393 circuit in either directions. I have seen many different electret mics online where both pins were clearly different since they were polarized but the ones I use don't have any such feature.
I am really bad with Op-amps but I know how headphones work, thank you. My project simply requires a speaker of around the same diameter as the mic.
chemelec:
If your Speaker is THAT SMALL, It must be Really Low Power.
Depending on its Impedance, the LM386 can Burn it out.
You might consider Adding a Series Resistor, to Limit the current into it.
Audioguru:
An electret mic has a diameter of 6mm or 9.7mm. In old cell phones they were half that and in new cell phones they are a tiny little spec. I have a very small speaker (squeaker) that is 25mm in diameter that was in over-the-ears headphones.
My very small speaker also works as a microphone but has no Jfet in it like an electret mic has so it has no polarity and works both ways like yours. Then you do not have an electret mic, yours is a dynamic mic that is a little speaker with a magnet on the back of it.
A dynamic mic does not need and does not want the resistor used to power the Jfet in an electret mic. Try removing the resistor that powers your mic to see if it works much better without it.
Here are some photos of electret mics:
Richard Crowley:
It might be time for some photos. There are literally hundreds (perhaps thousands?) of different small microphone capsules. We really have no clue what you have there.
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