There are many instances where a simple and reliable power amplifier is needed - rear and centre channel speakers for surround-sound, beefing up the PC speakers, etc.
I have to say from the outset that I do not agree with the use of weighting filters, since they are not (despite the claims to the contrary) an accurate representation of human hearing.
Preamp in this circuit design by use IC 1458 is amplifier from microphon signal will divide phase by transistor T1 BC109 via Emitter and Collector which is 2 channel .
