Audio amplifier

Discussion in 'The Projects Forum' started by Eddy boy, Mar 7, 2009.

  1. Eddy boy

    Thread Starter Member

    Nov 19, 2008
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    In this week,my assigned project is 3-stage audio amplifier.well the circuit diagram is attached...if any body like to comment,it would be greatly appreciated.
     
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  2. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,345
    Hello,

    Can you post a schematic in PNG (screenshot) format ?
    I can not use the attached format.

    Greetings,
    Bertus
     
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I used the free Linear Technology simulation program LTspiceIV to open, run and modify the amplifier.
    The original circuit has a few things wrong. I fixed them and now the amplifier works pretty well and is more sensitive so the input level is turned down. The frequency is only 5Hz. The output power at clipping is a whopping 180mW.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    180mW isn't too bad with a 5V Supply and 3 transistors. Do you have a Bode Plot of the response?

    What are the assignment requirements for gain and bandwidth?

    Did the one Audioguru made fix the issues?
     
  5. Eddy boy

    Thread Starter Member

    Nov 19, 2008
    11
    0
    It works well at 5hz (sin wave signal) but my task is to built a audio amplifier(having constant frequency response from 20hz-20khz).tommorow i will tell further details about gain,bandwidth,...
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    My simulation of my modified circuit shows an input of 0.2V peak and an output of 1.95V peak. So the gain is 9.75.
    The transistors work well up to 100MHz so the amplifier should have a bandwidth of at least 500kHz.

    It is a class-A room heater. Its max output at clipping is 180mW but its dissipation is 595mW even without any output. The dissipation in the load is 380mW even without an output.
     
  7. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    The above circuit from Audioguru does that and match your requirement.

    However, you would need to find a 10Ω DC coil resistance speaker and as a bonus get free heating from your speaker coil with the large constant DC current through it when the amp is idle.
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Are those efficiency levels what give tube amps the "warm sound"? :p

    I kid, I kid.....
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    Tubes radiate warmth which makes you feel warm.
    Their second harmonic distortion is liked by some people.
    Their high frequencies are reduced by their output transformer.
    Their fairly high output impedance does not damp the resonances of speakers and some people like the resulting boomy sound.
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Add "Really Easy to Fix" to the list. Unless it's a hybrid. In high school I had a part time job at the radio shop plugging tubes into the tester and sorting them, and some repair work. Most often it was the power supply, some things never change.

    I like tube based guitar distortion, but can't really tell the difference on a "typical home theater". Then again, I'm mostly deaf (really).
     
  11. Eddy boy

    Thread Starter Member

    Nov 19, 2008
    11
    0
    I am in great trouble ,audioguru my circuit does work well (and ur modified too) if you are good in amplifiers circuit design then give me suggestions...my old circuit was rejected by Sir and i have to make only a single stage audio preamplifier having a voltage gain of 40(using a 2n2222 npn transistor) ...your response would be greatly appreciated.
     
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