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How to enhance the input/output gain of Preamp circuit

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Sriguru Pattanayak

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Hi,

I have the following preamp circuit built but the gain of the ecm is not so good. I have to speak loudly and that to very close to the ecm. can anyone suggest how to enhance its gain? the diagram is dully attached.

Preamp1.jpg
 

jiripolivka

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I do not know the EC microphone used here. Those I know have two terminals, and the resistor to + Vcc is typically 12 k.
In your case I would try to put a 20 k resistor trimmer in place of 5k at ECM output to adjust a better output. I would also put a 10 u capacitor across R3 to increase gain.
 

Warpspeed

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Are you absolutely sure that the microphone you are using is the "electret" type ?
These have quite a high output voltage, much greater than many other types of microphones.
 

Sriguru Pattanayak

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Yes the model is philips LBC1055/00

Can u please mention with the part list code??
 
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FvM

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The amplifier circuit is basically fine. May be something is wrong with the used components. First step to check circuit operation would be to measure the DC levels with a multimeter, ECM and amplifier should show a reasonable bias point.
 

Audioguru

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The output level of an electret mic is about the same as from a dynamic or most other types of mic.
The circuit is found on a few sites in Google when looking for the Philips 3-wires electret mic. Its gain should be high enough for the circuit to feed a power amplifier or recorder that has a fairly high input impedance. What do you connect it to?
DO NOT bypass R3 with a capacitor because then the gain, noise and distortion will be much too high. Instead reduce the value of R3 until the gain is high enough and the noise and distortion are not too high.
 

chemelec

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Hi,

I have the following preamp circuit built but the gain of the ecm is not so good. I have to speak loudly and that to very close to the ecm. can anyone suggest how to enhance its gain? the diagram is dully attached.

View attachment 119211

Do you have this Pre-Amp Connected to a POWER AMP?

This Pre-Amp Can't drive a Speaker without a Power Amplifier.
 

Sriguru Pattanayak

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Do you have this Pre-Amp Connected to a POWER AMP?

This Pre-Amp Can't drive a Speaker without a Power Amplifier.


Yes it is connected through a 1w RMS Power Amplifier with a .5 watt speaker.

- - - Updated - - -

The output level of an electret mic is about the same as from a dynamic or most other types of mic.
The circuit is found on a few sites in Google when looking for the Philips 3-wires electret mic. Its gain should be high enough for the circuit to feed a power amplifier or recorder that has a fairly high input impedance. What do you connect it to?
DO NOT bypass R3 with a capacitor because then the gain, noise and distortion will be much too high. Instead reduce the value of R3 until the gain is high enough and the noise and distortion are not too high.

Can I add a variable resistor in place of R3? if so then what'll be the value??
 

Audioguru

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Yes it is connected through a 1w RMS Power Amplifier with a .5 watt speaker.
It is designed to drive a high impedance. What is the input impedance of your 1W amplifier?
If you increase the gain and the mic can hear the speaker then you will have acoustical feedback howling.

Can I add a variable resistor in place of R3? if so then what'll be the value??
Simply replace the 47 ohms with 22 ohms, 10 ohms or 4.7 ohms until the gain is high enough and the noise and distortion are not too high.
 

Sriguru Pattanayak

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it is designed to drive a high impedance. What is the input impedance of your 1w amplifier?
If you increase the gain and the mic can hear the speaker then you will have acoustical feedback howling.


Simply replace the 47 ohms with 22 ohms, 10 ohms or 4.7 ohms until the gain is high enough and the noise and distortion are not too high.

what about variable resistor??
 

Audioguru

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I have never seen a variable resistor that can be set to such a low resistance. Why do you need to adjust the gain? Doesn't your amplifier have a volume control?
 

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