Line level into really high input impedance

Discussion in 'Pro Audio' started by Lorin David Schultz, Dec 17, 2005.

  1. I've tried working this through in my head, and either it's just too
    early in the morning or I'm just too stupid to figure it out.

    "Typical" impedance for a line-level input is around 20K or so. A
    device I'm looking at has combo Line/DI inputs. The switch changes
    input sensitivity but not impedance. Thus the line inputs are balanced
    +4, but with an input impedance of 10 Megohms. What are the
    consequences of such a high input impedance (if any)?

    --
    "It CAN'T be too loud... some of the red lights aren't even on yet!"
    - Lorin David Schultz
    in the control room
    making even bad news sound good

    (Remove spamblock to reply)
     
    Lorin David Schultz, Dec 17, 2005
    #1
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  2. Lorin David Schultz

    Scott Dorsey Guest

    High cost. And probably slightly higher noise due to some of the design
    constraints involved in the super-high input Z.

    As long as the input Z is higher than or equal to the output Z, you are
    fine, unless you have a device with an output transformer that needs to
    see a particular load. In that case, a termination resistor across the
    input is needed.
    --scott
     
    Scott Dorsey, Dec 17, 2005
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  3. Lorin David Schultz

    Pooh Bear Guest

    None you need to worry about from the perspective of plugging it in and
    using it.

    That's an unusually high impedance. What's the unit ?

    Graham
     
    Pooh Bear, Dec 17, 2005
    #3

  4. Good. That confirms what I thought then. I looked up my notes from
    school (written with a quill on papyrus) and all I noted was that low
    into high is fine but high into low isn't (with the standard garden hose
    analogy). Nothing about what current issues might arise as a result of
    putting a bigger impedance across a fixed voltage. Needless to say, the
    little red schoolhouse I attended was focussed more on practical
    applications than technical theory.


    Right. I don't presently have any gear with a transformer output, but
    if I did, I'd be looking at matching.

    Thanks guys!

    --
    "It CAN'T be too loud... some of the red lights aren't even on yet!"
    - Lorin David Schultz
    in the control room
    making even bad news sound good

    (Remove spamblock to reply)
     
    Lorin David Schultz, Dec 17, 2005
    #4


  5. Digi 002R.

    --
    "It CAN'T be too loud... some of the red lights aren't even on yet!"
    - Lorin David Schultz
    in the control room
    making even bad news sound good

    (Remove spamblock to reply)
     
    Lorin David Schultz, Dec 17, 2005
    #5
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