Hello all . I am Facing a problem with MIC circuit. Ia using SIM908 GSM/GPS module for making call.the Electret MIC is connected to SIM908 modle through a preamplifier i.e.MAX4063. THe problem is im getting lot of noise in the call . when the moise reduces even the quality of the voice signal also reduces . please help me out in getting rid of this noise. the preamplifier and MIC is connected together in one board and sim908 module is in differnt board. pls help me to get ridof this noise.

 

Is it hum? Or just white noise? You need to pay particular attention to how the various equipment is plugged into the wall, if possible is a common outlet.

 

hi wendy,
its a some background noise . grrrrrrrgrrrrrggrgrgrgrgr like that. in my working room, RFID recever and few GSM antennas are kept . would that create any kinda interference to it?

can you tell how to get rid of the noise . as soon as i pick the call its starts grgrgrgrrrrrrrrggg like that. Do i have to change any input /ouput capacitor of pre amplifier?

 

it is rf feedback getting into the mic circuit. a few ferite beads and some bypassing should clear it up.

 

ok thank you very much . where excatly i should connect the capacitor or ferritr bead . i have attached the circuit as well.please help me .

 

it is rf feedback getting into the mic circuit. a few ferite beads and some bypassing should clear it up.

please go through the circuit and revert me soon . please

 

The microphone would be a good start.

 

The device pinout in your schematic is significantly different from the datasheet. For example, the outputs are on pins 4 and 8, not 2 and 7. I'm surprised there is any output at all.

ak

 

a ferite bead on each mic wire, and one on each output lead, as well as on the +5v lead. the preamp is piicking up the digital out put of nearby cell phones.

 

Hi,
Thanks for your reply.
The MIC is connected to Pre-amplifier input and the output is connected to SIM908 Module MICP,MICN . is it not correct?

 

Hi thanks for your reply,
what value of ferrite bead? can you brief me , low value will suppress high frequency?or how it is ? The ferrite bead should be connected to ground ?