Audio - Split and adjust only one output

Discussion in 'The Projects Forum' started by andyhof, Mar 18, 2016.

  1. andyhof

    Thread Starter New Member

    Jun 22, 2011
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    Totally noob here, so please be patient ! But you guys have been helpful before so here goes:


    I am looking at creating a splitter box for an unbalanced line level audio signal.

    organ rotary signal (+) ~4dBu
    audio ground (-)

    I would like to split the 1 signal into two separate outputs.

    One separate output would continue unchanged to organ speaker/amp.
    I would like the 2nd output to be controlled to vary its output (decrease) before it reaches the speaker/amp.

    So, in theory, I would like one input, two outs, with a volume pot on one output

    I understand (or have been told) that this cannot be done passively.

    Is there a simple circuit i can put together to accomplish this?

    I'm open to learning and welcome any suggestions.

    thanks
    Andrew
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    A volume control feeding the second amplifier will do, i take it there are two separate amps?
     
  3. andyhof

    Thread Starter New Member

    Jun 22, 2011
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    Yes 2 separate amps.

    I was told that it's not that simple and that I would need to build a buffer


    2 separate amps
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You can use an op amp as a unity gain buffer, dead easy.
     
  5. andyhof

    Thread Starter New Member

    Jun 22, 2011
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    Dead easy I like

    But since this is new to me..
    I need the circuit spelled out

    Should we continue off list in email so others don't get bored?
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    This
    is the simple buffer circuit, you put the input to the volume control wiper and the signal is altered.
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    I see no particular reason for the buffer amp, unless the reduced output is driving a long cable.
    Just run the signal directly to the non-altered output and use a pot for the second output (a 10kΩ or so pot should work).
     
  8. andyhof

    Thread Starter New Member

    Jun 22, 2011
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    0
    So, if i make a "daisy chain" splitter, and use a pot for the second output, that simple?
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,529
    1,248
    It can be. Here is a seat of the pants method for thinking about the voltages and components.

    If the audio source has a relatively low output impedance, and both amps have relatively high output impedances, then you can run the audio directly to amp #1, and through a simple volume control to amp #1. For example, if the source is an electronic circuit such as an opamp output stage with a 100 ohm series resistor to prevent damage from accidental short circuits as things are plugged and unplugged, then the output impedance is 100 ohms. If the input impedance to amp #1 is 100 K, then when it is connected the source voltage decreases 0.1%, trivial. If you also connect a 10K pot, then the source decreases 1%, barely noticeable. The worst case output impedance of a 10K pot is 5K, and amp #2 has that 100 K input impedance, so at 50% rotation (assuming a linear pot, which you would *not * use but it makes the math easier), the input to amp #2 will be 5% lower than the actual 50% audio voltage. But you don't care about that because it is an adjustable attenuator on purpose, so you turn it up a tiny bit to compensate.

    A voltage follower buffer or two make the two outputs absolutely independent, but there is no reason (yet) to make that your starting point.

    ak
     
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