How to increase mic sensitivity.

[elexboi]

In the attached circuit how can I increase the sensitivity of my mic.
from that reference I can only hear voice if I place my mouth too close.
Any smart suggestion will be appreciated.

Also,anyone can help me to my mic pre amp. Please refer to attached file. I also measure that the output of my preamp DC level is almost same as my VCC. While dc level in the input is half.

Thank you.

 

[Nigel Goodwin]

That already has a gain of 1000, what are you feeding the output of the preamp to?.

 

[elexboi]

Yes 1000 at unitless and 60 in dB. but my problem is I have to put the mic closer to my mouth.
Is there anyway to increase the mic sensitivity or I have to use high sensitivity mic?
This will be feed to the telephone chip for hand free with an internal gain of 8dB. Input impedance of transmit path was around 25KOhms.

 

[Nigel Goodwin]

You could use two opamps - but a gain of 1000 should already be plenty (if not too much) - so I suspect you have a problem somewhere?.

 

[elexboi]

Thank you. I need more inputs so while troubleshooting this one.

 

[DerStrom8]

Are you feeding the output of this pre-amp into an amplifier, or are you just trying to connect it directly to the telephone chip?

 

[elexboi]

directly to the telephone chip input (w/ 8db gain at its output for transmission)

 

[Nigel Goodwin]

Use a scope and check what's wrong then - either you're not getting the 1000 times gain from the circuit, or there's a problem with the output from the mike.

 

[Gary B]

The shape of the mike holder might also be affecting your results. If it is flat then it is probably picking up sound from 180 degrees. If you put it at the bottom of a cone, its angle of pickup will be narrower but sensitivity will also increase.

By the way, did you verify that this is not a noise canceling unit or one intended for noisy areas? Those are intentionally designed not to pick up any source that is not within a couple of inches of its diaphragm.

 

[audioguru]

Your schematic is missing a supply voltage. What voltage is it?
Why is R10 in series with the VCC pin of the opamp and what is its value?

 

[elexboi]

Your schematic is missing a supply voltage. What voltage is it?
Why is R10 in series with the VCC pin of the opamp and what is its value?

VCC = 5V
R10 = 0-ohm (short)

 

[elexboi]

The shape of the mike holder might also be affecting your results. If it is flat then it is probably picking up sound from 180 degrees.
The mic is facing downward, almost 6mm facing the surface (table). My usable gain was only 5.... (changing the value of 82 to 2K and 82K to 10K).
Increasing the gain causes strong noise.
If you put it at the bottom of a cone, its angle of pickup will be narrower but sensitivity will also increase.
Im using omnidirectional mic, is unidirectional may help reduce the noise?
By the way, did you verify that this is not a noise canceling unit or one intended for noisy areas? Those are intentionally designed not to pick up any source that is not within a couple of inches of its diaphragm.
If you wont mind can you explain this one, or maybe links that could help me to understand? Can you site sample schematic for noise cancelling?

 

[audioguru]

Maybe you have a condenser mic that needs to be powered with 48VDC. An electret mic (it has 48VDC built into its electret material and has a Jfet impedance converter) should be used with its two pins connected with the correct polarity.
A gain of 1000 in the preamp is much too high so of course it produces a high noise level.

Why is your mic facing the table? Look in Google Images at Boundary Microphone where thousands are shown with a low profile but with their electret mic is facing upwards or forward.

 

[elexboi]

I use electret type of mic and now I can control its sensitivity. The mic is located below the case thats why it face downward. But now the gain of mic preamp was only 10x. And higher gain causes feedback noise. Is there a quick fix for feedback noise?

 

[audioguru]

Acoustical feedback howling is caused when a microphone can hear the speaker and the sounds go around and around.
A speakerphone avoids feedback by turning off its microphone when the speaker plays the distant end and turning off its speaker when its microphone is talking to the distant end. A switch can be used between transmitting and receiving or a circuit can detect audio levels and make the switch. It frequently cuts off some words.

Modern speakerphones use a complicated digital echo canceller that makes a model of the acoustics in the room and of the acoustics of the hybrid and telephone line and cancels them. Polycom and other good (expensive) speakerphones use a digital echo canceller.

PA systems avoid feedback by turning down the gain (like you did) and having the people speak loudly very close to the microphone.

 

[elexboi]

Thanks a lot...

 

[elexboi]

Hello,

I encounter echo using this pre-amp, what is the main cause of this?

 

[audioguru]

I encounter echo using this pre-amp, what is the main cause of this?

Didn't I answer yesterday on another website?
You need simple voice-switching circuit or a complicated digital echo canceller circuit.