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Mixing 4 audio channels to 3?

Discussion in 'Electrical Engineering' started by DaveC, Oct 26, 2011.

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  1. DaveC

    DaveC Guest

    Why not go active and get rid of the caps altogether?

    Thanks John. Good simple design.

    Can you suggest a good op amp for such an audio application?

    Is it possible to use single-supply amps throughout?

    Thanks,
    Dave
     
  2. DaveC

    DaveC Guest

    Can you suggest a good op amp for such an audio application?
    No tools.

    I made the L & R op amps fixed gain and added input level control pots:

    <http://i43.tinypic.com/2hh3y12.jpg>

    Comments?

    Thanks.
     
  3. DaveC

    DaveC Guest

  4. DaveC

    DaveC Guest

    I used an LT1007 in the simulation.

    Can't find them on Mouser.

    Suggest another one that's good for audio?

    How about LM833? ::

    <http://www.national.com/ds/LM/LM833.pdf>

    The SR and GBW beat the 1007... ;-)

    Thanks.
     
  5. DaveC

    DaveC Guest

    Is the type of resistor important (wire wound, etc.)?

    Thanks.
     
  6. DaveC

    DaveC Guest

    Is it possible to use single-supply amps throughout?

    Only a single supply (in the amplified speakers) is available to power this
    circuit. I can tap this supply for my circuit:

    <http://i41.tinypic.com/2vlo2t2.jpg>

    I've added input & output caps. Are these values sound? ;-)

    How do I go about getting a 1/2 Vcc ground reference? (See my non-EE
    attempt.) What values to use for the divider resistors?

    What needs to be reference to the new "ground"? Everything between the input
    caps and output caps?

    Thanks,
    Dave
     
  7. DaveC

    DaveC Guest

    Latest rev:

    You do mean each of the op amps' *inverting* inputs, yes?
    Is this what you mean (see link)?

    Thanks.
     
  8. DaveC

    DaveC Guest

    Your drawing is wrong; signal goes to the inverting (-) inputs and the
    Thanks guys. Fixed:

    <http://i44.tinypic.com/r1k8qa.jpg>

    All else looks good?

    Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
    designs. Values for these?

    Thanks.
     
  9. DaveC

    DaveC Guest

    You still have the signal go to the non-inverting input.

    The current version of the drawing has signal going to the inverting input
    That means you're not looking at the right version of the drawing. Copy &
    paste this into a browser:

    Suggestions?

    Thanks.
     
  10. Don Pearce

    Don Pearce Guest

    What does U4 do?

    d
     
  11. DaveC

    DaveC Guest

    I'd eliminate C9. Some op amps aren't able to drive capacitive loads
    OK, done.
    Sound like basic good advice. :)
    I presumed that such coupling caps should be non-polar. No?

    Thanks.
     
  12. Bob E.

    Bob E. Guest

    What does U4 do?

    Provides a Vcc/2 local "ground" so I can use these op amps with a single
    supply voltage.
     
  13. DaveC

    DaveC Guest

    I'd also recommend decoupling your 16-volt power supply, with a .1 uF
    Since the V- pin is already PS ground, I need decouple caps only on the V+
    pins, yes?
     
  14. DaveC

    DaveC Guest

    First you can replace C1-[4?] with 1uF each. Replace C8 with 220uF, and
    Leave C5-7 as is?
    Teach this man to fish: why don't I want to use 50K pot & 10K load
    combination?
    "adjusting" means replace those with 100K's also?

    Thanks.
     
  15. Don Pearce

    Don Pearce Guest

    More useful to let it oscillate as a square wave generator at 100kHz
    or so, and rectify the output into a negative 15V rail. That way you
    can run the op amps the way they are meant to be run.

    d
     
  16. DaveC

    DaveC Guest

    More useful to let it oscillate as a square wave generator at 100kHz
    Suggest a circuit...?

    Thanks.
     
  17. DaveC

    DaveC Guest

    I was going to suggest that, since the mixer is going to be external
    Enough to suggest a nice circuit? ;-)

    Thanks,
    Dave
     
  18. DaveC

    DaveC Guest

    No need for that. You're going to have an 8-volt bias sitting on each
    I'm learnin'! Thanks for the explanation. I'll use standard aluminum 'lytics
    here, connected as noted.

    Dave C.
     
  19. Guest

    Hint: Don't use the chassis ground symbol as a "Vref" symbol. It's confusing
    and someone along the line might get hurt. Grounds should be.
     
  20. DaveC

    DaveC Guest

    Hint: Don't use the chassis ground symbol as a "Vref" symbol. It's
    confusing
    Yeah, I wasn't sure about that. How should I have indicated 2 separate
    grounds?

    Thanks.
     
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