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Re-amping with Radial JDI questions...

Discussion in 'Recording' started by ssbeeb, Mar 31, 2010.

  1. ssbeeb

    ssbeeb Guest

    I want to reamplify my DI bass recorded signal but I'm unsure how to connect everything. The manual says to hook everything up this way:
    I use a MOTU 828mk2 with my DAW and usually use either my ME-1NV preamp or my RNP. Would I plug an analog out from the MOTU into the preamp input(in place of plugging into the 'mixer') and then out to the DI or is the Motu AI acting as 'the mixer'? If that were the case I could therefore run from an analog out straight to the DI? Or have I missed it completely?
     
  2. ssbeeb

    ssbeeb Guest

    I figured out that I should be running straight out of the analog balanced out on the MOTU and into the DI output but now I do not know how to assign the output of the recorded track to send out to the DI. Is this something that I do in Logic or on the MOTU? I have Logic 7.2 Express and the MOTU828mk2.
    Any help would be great!
     
  3. Link555

    Link555 Well-Known Member

    Hi and welcome SSBEEB!

    Ok first ask yourself what does a DI do?

    It takes a unbalanced signal (1/4" TS-Guitar Plug) and makes it a balanced signal (XLR Mic Plug).

    Now some DI's are active some like the JDI are passive....

    Active DI's and powered via a battery and typically only allow audio pass in one direction, from the TS jack to the XLR jack.

    The JDI is a passive device, inside there is a Jensen transformer
    http://www.jensen-transformers.com/datashts/dbe.pdf

    You can pass audio in both directions with a transformer such as this.

    So what you want to do is:
    1) Take a analog out from your MOTU unit feed into the XLR side of the JDI.
    2) Take a guitar chord and plug it into the TS jack on the JDI ( don't use the speaker mode)
    3) Plug the other end of the guitar chord into the bass amp.

    As for the software side:
    Setup a output bus to send the bass sound out of the Analog out your want.

    Hit apple key + 2 to see the mixer view,enable the global button (top left) to see all the tracks drag the bar and find the bus tracks, double click on the bus and it will be added to the arrange window.
     
  4. Boswell

    Boswell Moderator Distinguished Member

    This technique can be made to work fine, but you need to take care not to overload the DI's transformer and/or the guitar amplifier input when re-amping with passive DI boxes. Radial does not give a turns ratio for the JDI, but a guess derived from the impedance figures would be 4:1. If there were no overloading, a +19dBu signal applied to the XLR connector from a MOTU TRS analog out would emerge from the TS jack at +31dBu, which is far too hot for an amp.

    When using a transformer-based passive DI box for re-amping, I normally use an attenuator in the XLR input, or else a passive volume control. One alternative would be to drive it from an interface output that has a genuine volume control on it such as one channel of a headphone jack. You need about 40dB of passive attenuation. Don't turn down the output amplitude digitally in your DAW, as this would just use a small range of the interface's DAC output, with resulting loss of signal quality.
     
  5. Link555

    Link555 Well-Known Member

    its 12:1

    I have a few Attenuators built one is 12:1 and one 30:1
    Here is a good site that details the design and construction....

    Uneeda Audio - Build your own attenuator pads
     

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