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What's the diff between passive and active direct boxs?

Discussion in 'Sound, Music, and Intercom' started by 9voltnewbie, Aug 30, 2003.

  1. 9voltnewbie

    9voltnewbie Member

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    I am going thru our inventory of equipment and I found two direct boxes. One is your standard whirlwind passive direct box (very nice :) ) and the other is also from whirlwind, but it says that it is an active direct box... What are the differences between the two and what situations would I use one over the other?
     
  2. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Hiya and welcome to the forum....

    Difference between the two DI's is primarily that one requires an external power source to operate--like a 9volt battery or phantom power from your console, and the other one does not need power to operate. The Active requires power--so its internal workings & wirings along with the transformer are ACTIVE--usually these have pads and circuits that need power to help it with the input signal, while the passive box simply uses a basic hi/lo transformer that requires no power to work except the voltage that is produced by the input source. Other differences--there may be some sonic quality difference between the two but its negligable for the
    most part.

    hope that helps!
    -wolf
     
  3. TechDirector

    TechDirector Active Member

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    I used to use a direct box when I play my violin in my band (check out my profile for details). And it never need a battery. Now I use a pre-amp which is basically the same thing but it does require a battery and I have the option to change the volume, bass, and treble coming from the pre-amp to the mixer. But I sure hate having to replace the battery every 4-5 times I use it.
     
  4. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    I checked your profile as suggested--didn't see a violin reference...but I did see you are also a baseball fan as I am. When I played on school or church teams, I was usually catcher or shortstop. =)

    FWIW, a pre-amp is a bit different then a DI is...you can do so much more with a preamp such as the volume and tonal quality changes you mentioned, where you can only change a signals impedance level with a DI. Some of the Active DI's have pads and phase shifters, ground lifts and filters, but thats as far as they go usually. Pre-amp is a much better choice but it is the second step in the sound chain, where a DI is in the first part of input transducers (speaking of input transducers--look for my basic sound tutorial coming to this BB soon as I am finished writing it--a shameless plug =) ).
    Ya--hate those battery changes..on DI's and everywhere else. But without that power for either a DI or a pre-amp--its just a doorstop. :lol:

    cheers mate...
    -wolf
     
  5. TechDirector

    TechDirector Active Member

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    Oh your right, it isn't in my profile, but under "TechDirector" in the "New Member" board. I guess I just figured it was there.In baseball I only played outfield; mostly center but sometimes "left-out"...........lol bad joke.

    Anyway I forgot that DI's can change the impedance. I guess it's been that long since I looked at one. lol. And your referance of a DI or a pre-amp as a doorstop without power, also a very expensive doorstep indeed. haha!
     
  6. 9voltnewbie

    9voltnewbie Member

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    I never learned what impedence and ohms (sp?) are... does anybody know that stuff or have a good link to a guide or something about that?

    Because I've got a reel2reel projector that we use and it has an 8ohm 1/4 output... how should that be hooked up to a sound board?
     
  7. wolf825

    wolf825 Senior Team Emeritus Premium Member

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    Hiya,
    well if you are looking for links you can read up on, I'll post a few good ones below on the topic to getya started...

    To answer your question (and try not to get techno-geek in terms): Impedance and Ohms are differeing measurements of Resistance, specifically the amount of resistance an electrical current experiences while it moves from one place to another. Specifcally--Impedance is defined as "the total passive resistance offered to the flow of electronic current". This would refer to the wire and circuitry that the electronic current passes thru--each has its own amount of resistance--kind of like a water hose that has something stuffed into the end--the water has to pass thru it to flow--but what it encounters can cause it to slow down or reduce in amount. Technically, impedance is determined by a combined measurement based on resistance and reactance(inductive & capacitance) in a given circuit... Some metals let electricity pass thru well, while others do not. Many factors can effect resistance such as wire thickness and compisition and distance as well as basic things like temperature...some things that heat up can cause a drastic change in impedance to an electrical circuit Ohms refer to an amount of resistance based upon calculations made from Ohms Law. Using Voltage, Current and Resistance in any combination, the math of two of those will give you the other. Ohms Law is the following:

    Voltage = Current X Resistance...say 14Volts = 2amperes X 7ohms
    Current = Voltage / Resistance...say 2amperes = 14volts / 7ohms ( / = divided by)
    Resistance = Voltage / Current...say 7 ohms = 14volts / 2 amperes


    Here area few links you can check out on your own...

    http://www.whirlwindusa.com/tech03.html

    http://ohmslaw.com/ohmslaw.htm

    also check out the STUDY HALL of www.prosoundweb.com for more tidbits of info...

    Your 1/4" reel to reel deck should have a LINE OUT that should go into a sound console 1/4" LINE IN.

    -wolf
     
  8. anticowboyism

    anticowboyism Member

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    Use a DI. Most have an Instrument/Amp switch - set it to amp, that's what your projector output is. Or some DI's have a -40db pad instead, use that.
     

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