Below is a schematic diagram of a speech amplifier circuit, we can also say it loud hailer circuit, megaphone circuit, bullhorn circuit, speaking trumped circuit or blowhorn circuit. This type of circuit is use to amplify the voice of a person in the crowd so every one can hear it. The circuit is using TDA7052
audio power amplifier IC to amplify the audio signals coming from transistor Q1. Q1 is amplifying the signals coming from microphone. The maximum output of the circuit is 1.2W on 6 volt. The resistor R1 is used to control the volume of the circuit, if you want to use electret microphone then R5, R6 and C6 will be used, C3 is used to reduce the feed back. J1 is an external microphone socket.  
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Parts List:
P1            =            22K Potentiometer
R1            =            1M
R2            =            15K
R3            =            470R
R4            =            47K
R5            =            4K7
R6            =            4K7
C1            =            100 NF
C2            =            100 NF
C3            =            10 NF
C4            =            100 NF
C5            =            220 uF
C6            =            10 uF
Q1           =            BC547
IC            =            TDA7052
J1            =            3mm or 6mm Mono Jack socket
SW1        =            Slider Switch
SPKR      =            4-8 Ohm Loudspeaker