AF Filter

This is an AF pre-amp and filter amplifier.  First stage BC547b is used as low noise af amplifier( here BC109c, in metalic pack gives good result). Second stage contains the OP AMP based filter with little gain. Third stage is also similar. From this AF is given to the standard LM386 amp which gives us comfortable audio.(this 386 amp is not shown here).

I used general purpose OP-AMP ic LM741 but when LF411 was used in first OP Amp stage it gave better performance then 741. At this ckt lower noise components helps tremendously.

This stages are powered from 12v DC , a well regulated sourse is must. there are few components on back side also.

It gives good Audio response. This is my favourite and reproduceable ckt block.