10 watt output quasi design

Discussion in 'The Projects Forum' started by simpsonss, Mar 16, 2010.

  1. simpsonss

    Thread Starter Active Member

    Jul 8, 2008
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    hi,

    this would be the quasi-complementary amplifier that i try to build it and observe it how it works.

    quasi1_pix.JPG
    http://www.sentex.ca/~mec1995/tutorial/xtor/xtor6/xtor6.html

    When constructing the circuit there are a few doubts.
    What rate of transformer that i should use for my power supply part which is not mention in the tutorial. Any idea everyone?

    And what is the watt rating that i should choose for all the resistors? Could 1 watt be a good choice?

    thanks.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    R4, R5 around 2W
    R6, R7 around 5W cement.... do not use wire wound type
    R8 2W
    others low wattage

    as for power... u can suffice with 1 amps. but do check the voltage for sagging.
     
  3. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    A few tips:-

    To get your 30V power supply, use a transformer with a 24VAC secondary and connect a bridge rectiifier and smoothing capacitor. Transformer and rectifier at least good for 1A or a bit more. Capacitor about 4700uF, 35V to 50V DC.

    Before you first power it up, make sure that R10 is adjusted so that the base of Q1 is connected to the collector.

    I would advise temporally connecting a wire-wound resistor of say, 470 ohms in series with the power supply when you first switch on. This will limit the current and save your transistors if there is a fault.

    The positive end of C4 should be at about half supply voltage. Adjust R10 until you get a small continuous current through the output transistors (about 50mA).

    When you are sure that everything is OK, then short out the 470 ohm resistor and try it with some audio.
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I hear ya.... but I still say he will blow the output before he can hear anything :D
     
  5. simpsonss

    Thread Starter Active Member

    Jul 8, 2008
    173
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    hi,
    thanks for all the replies. I would use a transformer with 24VA and 22Vac at the secondary voltage to get my 30V power supply.
    After calculating the watt for resistors R1 and R2 i will choose a 1/4 watt resistor for them.
    But what about the R3? how to calculate the watt across R3? Is it ~1.76mW?

    thanks.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    R3 is 470KΩ 0.25W will be OK
     
  7. simpsonss

    Thread Starter Active Member

    Jul 8, 2008
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    how do u actually calculate the watt across R3?

    thanks.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    experience
     
  9. retched

    AAC Fanatic!

    Dec 5, 2009
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    Ohms Law will help.
     
  10. simpsonss

    Thread Starter Active Member

    Jul 8, 2008
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    since the speaker i use is a 8ohm speaker. Can i connect the output to a 8ohm resistor to try before i connect the real speaker on to avoid any damage to my speaker?

    thanks.
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    You want damage any thing if you do exactly what post 3 says.
     
  12. simpsonss

    Thread Starter Active Member

    Jul 8, 2008
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    u mean which part? the 470ohm resistor after power supply that part?

    thanks.
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    exactly that
     
  14. simpsonss

    Thread Starter Active Member

    Jul 8, 2008
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  15. Audioguru

    New Member

    Dec 20, 2007
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    If the volume control R9 is wired correctly then it should adjust the volume smoothly from zero to maximum.
     
  16. dmccormick84

    New Member

    Mar 3, 2010
    11
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    Yes... I would use an 8ohm 20 watt resistor at a minimum. Many surplus outlets have hi-powered resistors at decent prices.
    dmccormick84
     
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    R9 is the volume and any 0.5W pot would suffice.
    R10 is a trip pot which is used to adjust the biasing of the drivers and power stage.
    The noise could be that your bias is too low which is heard as distortion
     
  18. simpsonss

    Thread Starter Active Member

    Jul 8, 2008
    173
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    hi,

    i change the R9 potentiometer from 4k7 to 5K7. then i manage to tune the volume lower.but still when i tune the volume to the lowest point the volume still too loud for me. Is it because of the bias part?

    thanks.
     
  19. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Are u hearing any thing from the speaker
     
  20. simpsonss

    Thread Starter Active Member

    Jul 8, 2008
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    yes.i input the audio sound from a DVD player to the input point.But it seems like the volume is too high even i tune the volume POT to the lowest.

    thanks.
     
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