Help: I want to build my own Intercom.

[masterleous]

Hi all,
i want to build my own INTERCOM, i teseted LM386 for Audio Power Amplifier and it is working perfectly, I want a Microphone for inputing a  Voice Signal, and from net i got a simple circuit for Mic Pre-Amplifier but the problem is that Noise is so much due to That Pre-Amplifier and Audio Level is so much low.
Can anyone tell me the right thing to take input from MIC, and which will outputed from Speaker through LM386.

I want only Mic Pre-Amplfier Circuit working properly, the rest of circuit (For Output) is designed and working.

Thanks

 

[audioguru2]

Hi Masterleous,
1) What kind of mic, electret or dynamic (coil and magnet)?
2) Is the noise coming from acousical feedback howling, background sound, electronic hiss or mains hum and buzz (from the wiring)?
3) What power supply voltage are you planning for the mic preamp?
4) Does your LM386 circuit have a capacitor beween its pins 1 and 8?
5) How much distance do you expect the mic to pickup voices?

 

[masterleous]

Hi Masterleous,
1) What kind of mic, electret or dynamic (coil and magnet)?
2) Is the noise coming from acousical feedback howling, background sound, electronic hiss or mains hum and buzz (from the wiring)?
3) What power supply voltage are you planning for the mic preamp?
4) Does your LM386 circuit have a capacitor beween its pins 1 and 8?
5) How much distance do you expect the mic to pickup voices?

Hi audioguru,
Thanks 4 ur Kind Reply......
1. I am using Electric MIC
2. & 4. I am using circuit for LM386 which is mentioned in it's Datasheet...........n also using a 10Uf cap in between 1 & 8. Noise is coming from MIC Circuitry, as i tested LM386 necessory circuitry from my SoundCard output and it is working properly without noise.
3. Power supply is 9v to 12 v.
5. Distance between person and MIC is normal 3-7 inches from MIC.

 

[audioguru2]

Hi Masterleous,
There is no such a thing as "an Electric MIC". What kind of mic, electret or dynamic? It might even be a carbon mic from an old telephone, or a crystal mic from a toy. They are all different.

You didn't describe the noise. If it is coming from the wiring then you need a shielded cable between the preamp and the LM386. Maybe the noise is coming from the power supply for the electret mic's load/supply resistor.

Please post the schematic for the preamp. If it has gain then the LM386 doesn't need the cap between its pins 1 and 8. 

 

[masterleous]

Hi Masterleous,
There is no such a thing as "an Electric MIC". What kind of mic, electret or dynamic? It might even be a carbon mic from an old telephone, or a crystal mic from a toy. They are all different.

You didn't describe the noise. If it is coming from the wiring then you need a shielded cable between the preamp and the LM386. Maybe the noise is coming from the power supply for the electret mic's load/supply resistor.

Please post the schematic for the preamp. If it has gain then the LM386 doesn't need the cap between its pins 1 and 8.

 

[masterleous]

Here is the Pic of PreAmplifier........

View attachment 36774

 

[audioguru2]

Hi Masterleous,
Your preamp is designed for an electret mic. It should have only two wires (some have 3 wires) and one of its wires is connected to its metal case which connects to ground at the preamp. Measure the DC voltage across your mic with a multimeter. It should be a few volts. If it measures zero volts or the power supply voltage, it is the wrong type.
The preamp circuit should have more than enough gain with an electret mic.

New electret mics don't cost much and look like this one, about the size of the end of a pencil:

View attachment 36776