SD8 hi-z question

  1. #1 by Steve Schow on 06-28-2018
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    SD8 hi-z question

    Alright, so I ordered an M32R today. Here I go...

    Thinking about adding an SD8 for home studio to plugin in keyboards, as we discussed on another thread. I notice that inputs 7/8 are high-Z. The question is what happens on 7/8 with XLR plugged in? In other words, for 7/8 i guess I will need to use a DI in between keyboard and XLR, to avoid the high-z instrument feed.

    Do I have that about right?

    At first I was a little annoyed by the high-Z, but now I'm thinking its kind of convenient that it basically has 8 DI's built into it, 2 of which are high-Z DI's... which can definitely come in handy and if you don't like it you can always just plug in mics to get around the built in DI's.

    Am i Understanding that correctly?
  2. #2 by Luc Henrion on 06-28-2018
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    Short answer: yes !
  3. #3 by Vasco Romijn on 06-28-2018
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    - Steve Schow wrote View Post
    ...I'm thinking its kind of convenient that it basically has 8 DI's built into it...
    There are no DI's built in the SD8/16. The TRS (jack) inputs are also balanced. You still need a DI because they usually do not have any ground- and potential-decoupling and just incorporate symmetrical input stages.

    If you do not have any noise by connecting directly a TR/TRS connector it will work fine without but telling there are DI's built in is not true.
  4. #4 by Anthonie Hunter on 06-29-2018
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    If you need ground- and potential-decoupling than Vasco is right: you need a seperate DI box.
    If you don't need ground- and potential-decoupling than the Jack inputs work fine.
    Just plug a mono Jack in the Hi-Z inputs for guitars and in the other inputs for line level instruments, like keyboards, samplers, etc.
    The mono Jack converts the symmetrical input in an a-symmetrical input by connecting Ring and Sleeve and it works fine.
    I use it all the time when instruments are close to my SD16.
  5. #5 by Steve Schow on 06-29-2018
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    Ok good point it’s not a transformer isolated di inside. I misspoke. In many cases it will remove the need for one though.

    one question, please excuse my ignorance, how can I know if I have a device that needs to be grounded and/or decoupled with an actual DI?
  6. #6 by Richard YClark on 06-29-2018
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    DIs are usually only needed for musical instruments with passive pickups installed like guitars and basses. These are usually also unbalanced and need HiZ inputs which the DI box sorts out. Also some headamps and/or keybaorads may have unbalanced line outs that may need to be fed some distance across a stage for instance. Here a DI can also help.

    Lots of acoustic instrument pickups these days are active and need phantom powering anyway. So they need to be fed into a mixer via an XLR mic connection.
  7. #7 by Steve Schow on 06-29-2018
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    balanced a line for long distances is a separate question and I agree...good idea to use a DI for that.

    Presuming that is not an issue, then under what circumstances do I need a DI specifically to handle, as mentioned above, ground and/or isolation?
  8. #8 by Craig Fowler on 06-29-2018
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    If there's a ground loop, eg if you've got a guitar with pedals and the pedals get power from the stage, but the mixer is somewhere else on a different circuit\phase (increasingly likely in venues like converted factories where power is all over the place) and there's some potential difference between the two grounds. Some devices (eg laptops) have noisy AC adapters too, regardless of which circuits they're on. Ground lifting can help here too. Sharing circuits with lighting gear (especially older dimmer racks) can also let noise into the PA. Ground lifting can help with this as well.
  9. #9 by Richard YClark on 06-30-2018
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    But again in these sort of cases you don't really need a DI as such because you don't really want to attenuate the audio signal and then have to amplify it again in a mic amp. You just need some sort of transformer box to decouple the input and output IMHO. I have found the Art DTI transformer boxes very adept at getting rid of the noisy laptop audio out PSU induced buzzes.