Attenuate white noise and EMI in audio circuitry

[elnino86]

Hye,

1) I want to attenuate the EMI effect on my circuit.The mobile phone signal distract my earphone where "tut" like pulse sound occur.The only method that i know is shielding.Shielding mean i need to cover up m circuitry using aluminum foil.It not changing any circuitry design.I need atleast some modification on my circuit to attenuate EMI effect.Is there any additional component should be add on any audio circuit to attenuate the EMI effect especially cause by mobile phone signal.

2) There is noise on my circuitry.I guess it is a white noise.However,another possibility is my condenser mic is pick up noise.Is there any way to reduce the noise or is there any way to produce a clean sound on for analog circuit?


I attached along my circuit concept.

 

[audioguru]

I can't remember the cutoff frequencies nor the gain of your bandpass filter.
The preamp has a gain of 105 and the power amp has a gain of 100 for a total of 105,000 which is extremely high and all the noise is amplified.
Metal film resistors produce less noise than carbon film resistors.

 

[elnino86]

My bandpass filter attenuate signal below 200 and above 20kHz..but i guess because of the energy level of the RF signal..it still distract my system.

 

[elnino86]

I can't remember the cutoff frequencies nor the gain of your bandpass filter.
The preamp has a gain of 105 and the power amp has a gain of 100 for a total of 105,000 which is extremely high and all the noise is amplified.
Metal film resistors produce less noise than carbon film resistors.

I have an idea here.I want to implement 2nd filter for my circuit which is high pass filter which will attenuate noise which dominated at low frequency. To reduce RF effect, i will use isolation technique which require me to shield the circuit using aluminum foil or sheet metal.

Can anyone comments on my idea?Do i "engineer" enough to solve the problem?

 

[audioguru]

Why is the gain so high?
Are you trying to hear people talking in the next country?
Are you snooping on people?

 

[duffy]

That gain looks way too high - 83k/800 on the preamp, all those filters all over the thing, another huge gain stage in the final amp... what is this for? Have you tried a much simpler circuit with lower gain? The way that mic's biased it looks like you're using an electret, which shouldn't need a voltage gain of 105,000 even driving a tower of speakers at a Motörhead concert.

 

[elnino86]

Why is the gain so high?
Are you trying to hear people talking in the next country?
Are you snooping on people?

I set the max dynamic range about 82dB.This is appropriate set value as i do a lot of test,reducing the pre amp gain down to 50 or 60 will make no much difference whether we using the device or not.To avoid to much gain,we may control it by using potential meter.

 

[elnino86]

That gain looks way too high - 83k/800 on the preamp, all those filters all over the thing, another huge gain stage in the final amp... what is this for? Have you tried a much simpler circuit with lower gain? The way that mic's biased it looks like you're using an electret, which shouldn't need a voltage gain of 105,000 even driving a tower of speakers at a Motörhead concert.

Although it had gain 105000,it doesnt sound like what you are thinking..The sound produce were quite smooth only that at full volume it suffer little peak clipping and noise were loud,SNR ratio seems smaller.

Are you suggest me to lowering the gain of pre amp?i will reduce it by 80,70,60 and 50 and see what i can get.

 

[audioguru]

The power amplifier has too much gain. Use an LM386 that has 1/5th the gain.
When the power amplifier is noisy and has too much gain then it amplifies its own noise and the volume control at its input does not reduce the noise.