I need help on my college project!

Discussion in 'The Projects Forum' started by mehtadhaval, Feb 8, 2008.

  1. mehtadhaval

    Thread Starter New Member

    Sep 21, 2007
    Hello everyone.
    I am new to this field & I have been asked to make one simple project on anything[only electronics]. & I have chosen this project on simple amplifier.


    But my problem is that the transistor they have used is not available on any store near to me :confused: . So instead of that which transistor I can use in it's place? :( Please help me out with this.


    Can anyone suggest me a project on simplest amplifier other than this?
    Thanks in advance. :D
  2. SgtWookie


    Jul 17, 2007
    It's still a homework assignment.

    We can't design it for you, but we can help you with it.

    The amplifier suggested is an obscure Darlington. As you know, Darlington pair transistors have very high amplification factors.

    (very big hint)

    You can use other Darlington transistors. They're basically on/off switches.
  3. Salgat

    Active Member

    Dec 23, 2006
    Find a darlington pair (or two NPN transistors in a darlington pair configuration) with similar specifications, I'm sure gain won't be an issue, as long as it's also NPN you should be fine. If you want to increase the "loudness" or amplification of the circuit, change the 50OHM resistor to a lower one, and be sure to use a transistor package that can handle more current.
  4. Audioguru


    Dec 20, 2007
    It is a horrible amplifier circuit.
    The speaker and 50 ohms resistor have 138mA in them. So the speaker's cone is pulled to one side. The battery won't last long if the amplifier plays or not.

    It is not biased correctly. The darlington transistor has a current gain that is typically 60,000 when its current is 138mA. Its base current is 64uA so the darlington transistor is very much saturated.

    The 50 ohm resistor makes 0.95W of heat and the 8 ohm speaker makes 0.15W of heat.