Does 2 mic malfunctioning ?

[AnalogKid]

Its a mixer circuit,

No, it is not.

There are three schematics on the page you linked to, and none of them are even remotely similar to your original schematic. Your schematic does not mix or combine or add anything. It is a subtractor. The output signal is the exact opposite of a mix.

ak

 

[MD MUBDIUL HASAN]

Why don't you understand that the opamp inputs must be biased at half the supply voltage so that their outputs can swing equally up and down??

I understand, we talk this issue before in other forum, but you were telling about 5v at first.

But when your your Mosfet turns on it slams the input of the last opamp to ground causing a huge negative going POP sound, then another positive going POP sound when the Mosfet turns off and when the input of the opamp returns to half the supply voltage.

Yes, when mosfet is turned on the last opams non-inverting inputs will go to ground. Do you mean at this time negative part of audio signal will amplified ?

You do not want the Mosfet to disturb the DC, you want it to mute the AC audio so add a capacitor between its drain to the biased audio at the input of the last opamp.

If I do so, how much POP sound can be minimized?
Is there any way to connect the MOSFET without interrupting any DC bias?

3.3V is a very low supply voltage for an audio circuit because any loud sound will cause extreme clipping distortion.

But many device contains such power, to make less power consumption.

I want to let you know other thing that, in old days people might be use transformer /coils to suppress the distortion, now a days can you suggest any tinny device ?

 

[audioguru]

I understand, we talk this issue before in other forum, but you were telling about 5v at first.

The amount of supply voltage does not matter. For a symmetrical output swing the opamp must be biased at half the supply voltage.

Yes, when mosfet is turned on the last opams non-inverting inputs will go to ground. Do you mean at this time negative part of audio signal will amplified ?

No.
The input signal to the opamp is shorted to ground by the Mosfet but the DC bias for the opamp is also wrongly shorted to ground. The Mosfet is used to mute the signal but I do not know why you need muting.

If I do so, how much POP sound can be minimized?
Is there any way to connect the MOSFET without interrupting any DC bias?

Of course, I told you to add a coupling capacitor in series with the drain of the Mosfet. The capacitor allows the Mosfet to turn on and off without affecting the DC bias but it is a short to the AC audio signal. When the Mosfet turns off then the capacitor does not affect the audio.

But many device contains such power, to make less power consumption.

Yes, but they also have a good automatic gain circuit so loud sounds do not produce severe clipping distortion.

I want to let you know other thing that, in old days people might be use transformer /coils to suppress the distortion, now a days can you suggest any tinny device ?

Absolutely NOT!
A transformer causes distortion, it does not suppress it.
A series coil reduces distortion because it blocks high audio frequencies and therefore also blocks the distortion harmonics. If a circuit blocks high frequencies then it produces no distortion but audio goes to 20kHz so you do not want to block the high frequencies.

 

[MD MUBDIUL HASAN]

Dear Sir Audioguru,

Thank you very much.
I am agree with you, I had little bit confusion.

I am thinking about to MIC input, do you have any other idea about less noisy action?
Do you suggest me this IC which has pre-amp and noise canceller inside, https://www.ti.com/lit/ds/symlink/lm49155.pdf

A series coil reduces distortion because it blocks high audio frequencies and therefore also blocks the distortion harmonics

If a circuit blocks high frequencies then it produces no distortion but audio goes to 20kHz so you do not want to block the high frequencies.

Maximum how mach high frequencies will block?

 

[audioguru]

I could not find detailed spec's about the LM49155 extremely small IC made for cell phones. It has 36 tiny "bumps" on its bottom for a computerized robot to solder.

You said you have a microphone inside and another microphone outside. You subtract their signals to try to reduce "noise" but what noise will be the same to both microphones? Outside my home I hear noise from traffic, kids who are playing, dogs barking and ambulance sirens. None of these noises are heard inside my home. My home has low level noises from the furnace and TV playing that are not heard outside. Therefore I cannot use two subtracting microphones to reduce any of these noises.

 

[MD MUBDIUL HASAN]

You said you have a microphone inside and another microphone outside. You subtract their signals to try to reduce "noise" but what noise will be the same to both microphones?

Yes, sounds reasonable issue.
I am going to make the pcb of previous one, let me see how it works.
After then, I will think this issue for further development.