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Discussion in 'Electronic Basics' started by Darths Jordan, Jan 23, 2006.

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  1. Can someone give me direction on this?

    I want to build a circuit that allows me to remix(?) left and right
    channels from a normal stereo in a custom fashion. In other words, I
    would have 4 knobs: one that controls level of left channel to right
    ear, one that controls level of right channel to right ear, one that
    controls level of left channel to left ear and one that controls level
    of right channel to left ear.

    Can I do this with a buffer (simple op amp) circuit maybe (4 total op
    amps) with pots to control gain?

  2. BobG

    BobG Guest

    Maybe buy an inexpensive DJ mixer with pan on the line inputs?
  3. David Harmon

    David Harmon Guest

    On 23 Jan 2006 18:12:24 -0800 in sci.electronics.basics, "BobG"
    What part of "I want to build" don't you understand?
  4. BobG

    BobG Guest

    I predict you will be unhappy with the results of repanning existing
    mixed and panned left and right channels, but I understand you want to
    build something, evidently. Maybe someone else has some ideas. I feel
    suffciently chastised for saying anything at all.
  5. Bob Masta

    Bob Masta Guest

    More or less. You can probably get away with only 2
    op amps, for L and R output summers. Each would sum the
    outputs of its own pair of L and R input gain pots. If
    you use simple inverting summers, then of course the
    outputs will be inverted. If that matters (and it sometimes
    does) you can follow each summer with another inverting

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
  6. I greatly appreciate any leads on raw circuits, kits or full devices

    I'm really hoping to have something I can power with a 9V battery and
    use it with an ipod-like device

    I have to apologize for asking really dumb questions, but I'm a real
    amature at this stuff.

    So would I be able to use a circuit like that shown in:

    I would use one of these for each stereo channel - but then how would
    I mix the signals? I assume I can't just connect the outputs from the
    two circuits to mix them correct? Since there is feedback on the opamp
    circuits, wouldn't this mess up the circuits?

    I guess that is what confuses me at a very basic level - is isolation.
    How can signals be mixed (combined) without feeding back to the other
    signal? I see if you use an opamp then you are really buffering the
    original signal and recreating it with another power supply. But then
    if you combine outputs (physically connect them) from the opamp
    buffers (to mix signals) you would mess up the function of the
    individual circuits.

    Sorry to ramble - I'm not smart enough to see how this works exactly

    thanks for all the help guys
  7. You already got the correct lead on a full device. A mini-mixer, for less
    than $50, will do exactly what you need. (An example would be the Behringer

    If you really want to build it yourself, you should understand that the
    parts will probably cost you more than that and the quality you'll end up
    with will be much lower.

    Ah, more requirements emerge. Must be powered with single 9V battery. Any
    other requirements, while we're at it? For instance, does the output need
    to be able to drive headphones? Need to be small and portable?

    A Rolls Pro Mix IV mini mixer will run on two 9V batteries, and it has a
    headphone output, and it is small. But it costs $150.

    That *idea* would work as part of your circuit. But you'd need to change a
    few things. For instance, that circuit requires a split power supply, e.g.,
    two batteries rather than one. (The supply circuitry isn't shown at all;
    the thing that makes it clear is that the non-inverting inputs of the opamps
    are taken directly to ground, rather than to a bias voltage, and there is no
    DC blocking capacitor on the input or output.)

    So, take a look at "mixer" circuits. The idea is that you'll feed each
    channel individually into one of your panpot circuits, and then you'll use a
    mixer circuit to mix the panpot left channels together, and likewise the
    panpot right channels together. And then, if you need, you'll use yet
    another stage to power the headphones.
  8. So if I take the output of the circuit in panpot.pdf (one for each
    stereo channel) and feed it to:

    I should be OK?

    Stupid follow-up question:

    In the mixer circuit, isolation is performed by just the resistances?
    This keeps the opamps from being affected by the connection of the
    channels in the mixer?

    I guess I might be confused because the currents are almost zero
  9. Rich Grise

    Rich Grise Guest

    This is sci.electronics.basics - note "basics". No question is unwelcome
    here, albeit we do frown on spammers and flamers. ;-)

    The only "dumb" question is the one you don't ask. :)

  10. Rich Grise

    Rich Grise Guest

    What you use is a "summing amplifier", where the inputs converge through
    resistors at the opamp's input.

    Here's an example:

    The inputs are perfectly isolated from each other, because the opamp will
    output whatever voltage it needs to to make the differential voltage from
    the "-" input to the "+" input equal to zero. The 3.3K is only to equalize
    the bias currents; it's equal to the parallel combination of the three 10K

    Hope This Helps!
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