new student amplifier circuit question

Discussion in 'General Electronics Chat' started by todmeg, Sep 20, 2009.

  1. todmeg

    Thread Starter New Member

    Sep 20, 2009
    on a multi-stage amplifier circuit, how do i identify the beginning of each stage. In other words, how do I identify the end so I can tell how many stages of amplification in a given schematic. Thanks in advance.
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    Can you post a schematic of an example circuit for the purpose of discussion?

  3. todmeg

    Thread Starter New Member

    Sep 20, 2009
    hope this works
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
    This amp is a 3-stage audio amplifier.
  5. todmeg

    Thread Starter New Member

    Sep 20, 2009
    Thank you for the response. My teacher is kind of cryptic on his explanation. how do I tell it is a 3 stage? What in this circuit is separating the stages? would it be the common emitters? Do those two in series count as one common emmiter in that particular stage? again... thanks in advance.
  6. Audioguru


    Dec 20, 2007
    It is an extremely simple audio amplifier with horrible performance.
    You should be able to identify its stages just by glancing at the schematic.
  7. todmeg

    Thread Starter New Member

    Sep 20, 2009
    Thanks everybody. This is more for example to identify than something that will do a good job. Your response will help me to learn and in the )near) future, I'll be picking these off. New to this game but loving every minute of it.
    Scott <------real name
  8. kkazem

    Active Member

    Jul 23, 2009

    In order to tell the number of stages, you count the number of amplification stages. The first two are easy as they are single transistor, but the last stage is a complimentary BJT emitter-follower. You have to recognize that it is a single stage, since it has an input from the previous stage's output and it in turn, has an output. Therefore, as mentioned above, it is a 3-stage amp.

    Generally, any amp stage has an easily recognizable input and output, even if it is made from a stage with more than one active device (transistor). Try looking at a few multi-stage amp schematics and practice trying to identify the input and output nodes for each stage and you should catch-on quickly.

    good luck,
    Kamran Kazem
  9. todmeg

    Thread Starter New Member

    Sep 20, 2009
    Kamran Kazem <---- my hero
  10. harsha429

    New Member

    Sep 19, 2009
    actually there is a resistor or a capacitor across the o/p of the transistor i.e at collector or base or emitter based on the configuration . so whare v connect load or coupling capacitor i.e next stage amp.
  11. steveb

    Senior Member

    Jul 3, 2008
    It takes experience to know, and eventually it becomes second nature. As you get more an more familiar with different designs, you will be able identify key features that define and separate stages.

    We could draw an analogy to a similar question. How many rooms are in a house? It seems so simple, unless you don't know the important attributes of a room. An inexperienced person may not know that a closet, or a hallway, is not a room. Similarly, he may not know that one big open area is not one room but a living room and dining room, separated by the functions associated with table and chairs versus the sofa and TV. Is the basement a room? What about the attic?

    Distinctions and dividing lines are not always clear. Sometimes they are arbitrary, ambiguous or approximate.

    In your example, coupling capacitors are a good indications of stage separation, but there is no coupling capacitor between your second and third stage. A single transistor defines the first two of your stages, but the third has more than one transistor. Your example uses fairly standard stages, so most people with experience can see it instantly. However, a specialized design can be confusing to anyone (especially if it is drawn poorly) and it may take a little analysis to figure out the separate stages and their functions.

    By the way, it is good practice to make the stage separations clear. This is just common courtesy. There are very competent and smart people that may not have your particular training and experience. For example, a digital designer may not know the details of analog circuit design. Or, a repair technician may want to troubleshoot from a high-level stage-by-stage approach. Why make things difficult for them?
    Last edited: Sep 22, 2009