Application:
I am working on wireless voice communication using MC52i Cinterion module, using analog interface-2(i.e micp2, micn2, epp2, epn2) for microphone and speaker. Microphone is working fine, but speaker need audio amplifier,and the amplifier is producing noise, hiss and hum along with the amplified output. I tried a lot to get the clear output but still problem exist.
Without amplifier voice is clear but the volume is very low.
Specifications for amplifier circuit
IC: LM4890
Vs:- 5 Volt
I also tried with other amplifier Ic but the result is same.
I attached schematic diagram of MC52i and circuit diagram of audio amplifier using LM4890, which i used.
so plz help me regarding this.

 

in your second picture, did you connect the input of the audio amplifier to where the internal loudspeaker is drawn to? What is that internal speakers impedance ? Is it also connected?

 

yes i connect the input of the audio amplifier to where the internal loudspeaker is drawn to. I dont have any idea about What is that internal speakers impedance. LM4890 is also recommended by siemens.

 

The loudspeaker output of the GSM module doesn't seem to be referenced directly to ground. You are connecting one output pin to ground.

forget the loudspeaker output and try to connect your audio amp to the headphone output, refer to the attached picture. there is still the "ring" contact, I don't know what's that for. If you have a datasheet for the GSM module post it.

 

I have referred the attached picture; I have one doubt in that picture is, the point marked for the connection to the ground of audio amplifier is “MICP1”, which should be used for microphone and act as an input.
I have attached datasheet for the GSM module, plz refer that.