As @Ice-Tea mentioned, we have not the slightest clue whether you are talking about one-off hobby "projects" or commercial devices (large- or small-scale).

Remember that forums (especially like this EEVblog Forum) are a gold-mine of information, quite possibly exactly what you are asking for. Remember also that many circuit stages are available as small, board-level modules that save you the time, effort, and expense of designing and building for yourself.