Transistor as amplifier's (cont.)......!!

Discussion in 'General Electronics Chat' started by RRITESH KAKKAR, Jul 11, 2011.

  1. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    Hello again,


    I want to make a amplifier using transistor, now it should have loud sound then earlier circuit given by Audio Guru and i don't want to add ready made chip in it....!!


    thanks
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    My extremely simple circuit is loud only when you hold the speaker to your ear. Its output power is only 0.42W like a cheap clock radio. Its power is a little more with a 12V supply but then the small output transistors might melt.

    Its distortion is very high at 10% when it plays loudly while an IC amplifier has many more transistors for very low distortion.
     
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  3. radiohead

    Active Member

    May 28, 2009
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    You could feed the weak signal into this chip for a little more volume. See the typical circuit on the datasheet. I know you don't want a chip, but this is as simple as it gets...

    For transistor circuits, see this link... http://www.discovercircuits.com/A/a-audioamp.htm
     
    Last edited: Jul 12, 2011
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  4. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    It should drive 12 inch woofer or less will also work, but there should not be any ready made amplifier chip used in it, it can have transistor transformers, darlington,......
    and i would like to design the circuit rather then copying same..!!
     
  5. Audioguru

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    After you learn about how transistors work then you can design an amplifier.
     
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  6. RRITESH KAKKAR

    Thread Starter Senior Member

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    I can use transistor as a switches, please.......AG tell me how to design transistor as audio amplifier.
    you know very well........
     
  7. debjit625

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    Apr 17, 2010
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  8. SgtWookie

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  9. radiohead

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    That's a great link, SGT Wookie. Thanks.
     
  10. RRITESH KAKKAR

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    Is there any diff. in working, of both common emmiter amplifier.??
     
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  11. SgtWookie

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  12. Audioguru

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    The transistor on the left side has an important emitter resistor that adds DC negative feedback. Then the transistor's operating point is not changed much when different transistors are used (even with the same part number) and when they have different Vbe and different hFE. The Vbe of a transistor changes when the temperature changes and the emitter resistor cancels most of the change.

    The transistor on the right side does not have an important voltage divider for its base voltage so its is saturated if its Vbe is low. It is also saturated if the hFE and/or if the supply voltage and/or if the temperature is high. Most of us were taught to NEVER bias a transistor like that.
     
  13. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    I have readied this article...
    Now please tell how to make amplifiers of nearby 5 watt??
    In my course book i have studied coupling stages in amplifiers like transformer, RC, etc.....
    The amplifiers can have active devices like transformer, Darlington, MOSFET,transistor,etc... but i don't wont to use chip..
     
  14. Audioguru

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    Modern power amplifiers do not use coupling transformers nor coupling capacitors. They are DC-coupled. The input and output might have coupling capacitors.

    Use simple arithmatic to calculate the voltage swing in an 8 ohm speaker to produce 5W. It is 17.9V peak-to-peak. The peak current in each output transistor is 1.1A. The output transistors have a small voltage loss of about 2V each so the power supply must be about 22V.

    The amplifier circuit has a complementary pair at the output which is an NPN transistor in series with a PNP transistor that operate push-pull. They are biased with two series diodes or a transistor and driven by a driver transistor. The input is a differential using two transistors or a single transistor which makes it simpler. Negative feedback reduces the distortion and sets the gain.
     
  15. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    IIRC this was a good article about the basics, but I cannot see the pictures, so it is not that useful anymore.

    A good starting poing could be, who could guess it, wikipedia, which shows a basic audio amp topology, along with links to details of each part.

    If I can recommend download this simulator as it is very easy to use, build the circuit from wiki and play with the values before building it. There are many examples included, so you should be able to simulate things very soon.
     
  16. RRITESH KAKKAR

    Thread Starter Senior Member

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    I think then, This circuit will work by changing its supply power and output transistor in common collector modes, but which no.??
     
  17. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    1) Audioguru already told you what supply voltage you need.
    2) I recommend using the Long tailed pair on the input, because that will allow for much lower distortion than the negative feedback, created by R1 if that is what I think it is.

    The output transistors will likely need to be changed, but for now that doesn´t change the simulation much. For example this is what your circuit could look like in the end. Q9 is a better substitute for the two diodes you have there, while Q3 acts like a constant current source instead of a single resistor that supplies the LTP.

    For your kind of power you probably don´t need the darlington outputs and single transistors will be enough.

    Disclaimer: I am no guru in transistor circuits, but what I know should be enough to make a working amplifier.
     
  18. Audioguru

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    My simple amplifier schematic has a 9V supply and an output of only 0.42W with a horrible 10% distortion. Its output transistors are tiny and will melt if used in a 5W amplifier. The driver transistor does not use enough current for a 5W amplifier.

    The 25W amplifier with Mosfet article has a horrible attempted translation into Engrish and does not use Mosfets.
    It has a trimpot to make it a class-A heater, a good class-AB audio amplifier or a class-B distortion machine.
     
  19. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    I was just looking about Long pair in Google, It has two transistor like diff. amplifier for increasing common mode rejection ratio......
    This long tail only create less distortion or ....???
     
  20. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    reply.......
     
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