Hi all, I am very new to this board, and new to electronics in general.
I set out to make a simple analog intercom system between two locations, distance is 20 meters or so, I've bought the appropriate cables, tested them and saw they have low resistance(like 2.2 ohms at most) and no detectable voltage drop over this distance with a 9v battery. The speakers I chose actually are not powerful enough, they are 4 Ohm 0.15w speakers, so I will have to buy at least 1-2w speakers.
I have built a preamplifier circuit from a single NPN transistor in common emitter configuration, it's a BC413B model with an hFE of 100. I admit when it comes to amplifiers from transistors I am still not familiar with the math, except the RC time constant and cutoff frequency math.
The microphone I am using is just an ordinary electret microphone, I don't have any specs but I believe it's range is 10-30 or at most, 60mV, which with a gain of 100 is 100-300-600mV peak to peak I believe.
Here is a working simulation of the circuit(you will need Chrome to view it) http://everycircuit.com/circuit/5814088627126272/what-is-wrong-with-this-preamp-circuit
The RC circuit on the collector actually gives me a cutoff frequency of 33Hz, but I don't have a ~80uF capacitor for ~20Hz, and the bypass capacitor at the emitter should give me the maximum gain of this transistor, or 100(I have not done the math, but some tutorials I watched said it should). The volume of the mic is still very low, I can barely hear the sound when rubbing the microphone or blowing at it.
If you are wondering why I didn't just buy an LM386, it was because I wanted to learn electronics and build this from scratch, however if need be I do have an AN7312 amplifier I pulled off from an old radio & cassette player.
What the simulated circuit doesn't show is that I hooked up the output of the first transistor to another transistor in a common collector configuration for current amplification, the volume was higher, but still could not produce any audible sound when I speak.
So I turn to you guys for help on how to make this circuit amplify more, and yes I do have more transistor of the same model, albeit they are all NPN.
I set out to make a simple analog intercom system between two locations, distance is 20 meters or so, I've bought the appropriate cables, tested them and saw they have low resistance(like 2.2 ohms at most) and no detectable voltage drop over this distance with a 9v battery. The speakers I chose actually are not powerful enough, they are 4 Ohm 0.15w speakers, so I will have to buy at least 1-2w speakers.
I have built a preamplifier circuit from a single NPN transistor in common emitter configuration, it's a BC413B model with an hFE of 100. I admit when it comes to amplifiers from transistors I am still not familiar with the math, except the RC time constant and cutoff frequency math.
The microphone I am using is just an ordinary electret microphone, I don't have any specs but I believe it's range is 10-30 or at most, 60mV, which with a gain of 100 is 100-300-600mV peak to peak I believe.
Here is a working simulation of the circuit(you will need Chrome to view it) http://everycircuit.com/circuit/5814088627126272/what-is-wrong-with-this-preamp-circuit
The RC circuit on the collector actually gives me a cutoff frequency of 33Hz, but I don't have a ~80uF capacitor for ~20Hz, and the bypass capacitor at the emitter should give me the maximum gain of this transistor, or 100(I have not done the math, but some tutorials I watched said it should). The volume of the mic is still very low, I can barely hear the sound when rubbing the microphone or blowing at it.
If you are wondering why I didn't just buy an LM386, it was because I wanted to learn electronics and build this from scratch, however if need be I do have an AN7312 amplifier I pulled off from an old radio & cassette player.
What the simulated circuit doesn't show is that I hooked up the output of the first transistor to another transistor in a common collector configuration for current amplification, the volume was higher, but still could not produce any audible sound when I speak.
So I turn to you guys for help on how to make this circuit amplify more, and yes I do have more transistor of the same model, albeit they are all NPN.