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Active vs. Passive DI

Discussion in 'Recording' started by MilesAway, Oct 11, 2005.

  1. MilesAway

    MilesAway Guest

    Hi - I've never been able to get a straight anwser out of anyone regarding which type of DI is best suited to which situation. I'm shopping around for one right now and here's what i need it to do:

    While tracking guitars, I keep my preamps (guitar preamps...) in the control room and have my power-amps & cabs located in my soundproof booth several rooms away (~75' of cable). What i'd like to do is run guitar--> preamp (distortion, tone-shaping), then into a DI box for the long cable run, then into the poweramp/cabs. The DI box would have to handle a fairly hot line-level signal coming out of the guitar preamps (JMP-1/Triaxis/Rockmaster).

    What should i be looking for? Active or Passive?

    -Dave
     
  2. Kev

    Kev Well-Known Member

    describe the power amp

    If the power amp is a typical guitar power amp the the input impedance and power transfer is easy even at high levels.

    A passive transformer coupling will do the trick.
    If the power amp has a very high input imp and is suseptable to external or internal thermal noise then it could all get tricky even with an active FET type unit.

    There is no SINGLE correct answer here.

    My gut feeling here is that your favourite DI box at the source with true balanced output and a simple 1:1 Transformer coupling box at the destination with a quality sheilded balanced cable will give good results.

    An earth lift option in this second box is a good thing.
     
  3. MilesAway

    MilesAway Guest

    Thanks for the info.

    The poweramps in question are Peavey Classic 50/50 and Classic 60/60 models... pretty standard config/setup from what i can tell.
     
  4. Kev

    Kev Well-Known Member

    These are basic guitar power amps designed for unbalanced guitar pre to guitar power levels.

    Generaly lower than 600 ohm Line levels.

    Either a passive or active DI box will get this unbalanced signal to balanced ... for the long run.
    The buffering provided by the active DI box is probably not a must
    BUT it doesn't do any harm either.

    At the other end a simple 1:1 transformer will unbalance this and provide the Common Mode Rejection (CMR) to cancel noise

    Probably should be
    150 ohms : AS high as possible
    but
    600:10k
    or
    600:600
    will probably work and work fine


    the Rane Site may have some info on coupling
    have a surf
     
  5. RemyRAD

    RemyRAD Guest

    Having done something similar numerous times in the past, the preamplifiers output should be fed via a balanced, microphone type output and cabling. This can generally be done with a un-balanced 1/4 in. to balanced XLR adapter, transformer isolated to your power amplifier input, with another balance XLR, transformer isolated to 1/4 in. into the amplifier (the transformer isolated adapters, can be run forward or backward). The reason I recommend the transformer isolated variety like a "Whirlwind Director" is that you also have ground lift switches since you are probably going to encounter ground loop problems, which will induce terrible hum, all the while while being transformer isolated. Which is something you cannot accomplish with an active direct box and you cannot run the active boxes forward or backward but only in one direction. I also do not recommend plugging a guitar output into these transformer isolated direct boxes because the guitar requires an extremely high impedance input, in the area of 1 to 2 million ohm input, while the transformer type are generally between 10,000 and 30,000 ohm, oading the guitar pickups down.

    Having 2 transformer isolated direct boxes and 1 active direct box, should always be in your audio toolbox.

    Are you more confused now?
     

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