Audio mixer using op amp

Discussion in 'Homework Help' started by ishaan3731, Oct 13, 2012.

  1. ishaan3731

    Thread Starter Member

    Jun 23, 2011
    43
    1
    i made a audio mixer that mixes output from two mobile phone.... i used single channel from both mobiles as inputs to the summing amplifer.

    The circuit does the mixing work but the output is too low.....i had to remove my headphones and plug my speakers. My speakers at their full volume atleast showed the circuit works but still output was too low......

    Plz verify whether this circuit is ok to use as audio mixer...ie its resistance values etc!!!!

    i have used ne5532 low noise op amp!!!

    "The outputs cumming low does that have any connection to impedance matching between speaker and my circuit???"
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Why doesn't your schematic have a power supply? Unpowered opamps DO NOT WORK!

    If the opamps are powered with a dual-polarity supply and the volume control is at maximum then the output level will be exactly the same as the input level if it drives a load of 1k ohms or more.

    The output opamp cannot drive headphones and it cannot drive a speaker. It can drive a power amplifier that has an input resistance of 1k ohms or more. Then the power amplifier drives the headphones or speaker.
     
  3. CircuitZord

    Member

    Oct 8, 2012
    59
    2
    Somehow that made LOL, literally. :D
     
  4. ishaan3731

    Thread Starter Member

    Jun 23, 2011
    43
    1
    This is just a schematic of the concept not the project as a whole...i very well know that op amps require dual supply henceforth i have used 7805 and 7905 to produce +5 and -5V supply(not shown in schematic)..... my speakers have their own power supply and can be connected to mp3 players , mobile phones , computer ,laptops etc!!! so my op amp doesn't need to drive that....it just takes input from op amp's output and amplifies it!!!!

    Basic thing what i am asking is that doest a self power driven speaker and subwoofer set require impedance matching or not!!!!
     
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    You probably don't have enough gain.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    The output impedance of a mixer is usually extremely low. But the input impedance of an amplifier is usually fairly high. When they are connected then there is little voltage loss so the impedances are NEVER matched.

    The same for the output of a power amplifier, its impedance is very low, 0.04 ohms or less. Then when it drives a 4 ohm or 8 ohm speaker its very low impedance damps the resonances of the speaker and causes little voltage loss.

    You need more gain. It is simple to add gain to your mixer circuit.
     
  7. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    You might want to view this Application Note
     
  8. ishaan3731

    Thread Starter Member

    Jun 23, 2011
    43
    1
    I wanna ask something : in the schematic I have attached before are the potentiometer and the 10k resistor attached after the capacitor are in series or parallel !!!!!! if they are in series they decrease the gain as gain=Rf/R1 and if in parallel then R1 will always be less than 10k so the gain will be higher as compared to former case.
     
  9. ishaan3731

    Thread Starter Member

    Jun 23, 2011
    43
    1
    Thank for suggestion....So if I increase the gain of second inverting amplifier to 10 will that be enough because now the gain of mixer will get multiplied with 10.(if gain of ten from second inv op amp is sufficient so what gain or do I require more op amps with gradual gain increase).....
     
  10. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    They are parallel so your signal source must be able to drive 5k ohms which is pretty low.

    I don't know the output level from your mobiles so I don't know how much more gain you need.

    Your circuit does not need the second inverting opamp. Increasing the value of R5 will increase the gain of the first opamp.
     
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