Direct Box, passive

[godd2]

Hello,

I have a number of DI boxes and I am really not sure how they work or what for. I do not do anything with guitars or whatever. I work at a high school and do stuff with dvd players being connected to the theater sound system. is this something these could be used for?

 

I am just lost really what they are for.

 

thanx

[MarkPAman]

Does the Blue Room Wiki help?

 

:P

[jodat2]

Because the mic inputs on a mixer have a much lower impendence than a line input, the DI box takes a line signal (such as one from a bass, guitar, keyboard etc) and increases the impendence so that the mic input on the mixer will handle the signal.

 

DI's are commonly used on Bass guitars, acoustic guitars, Synths and keyboards. An advantage of a DI as it means you are not going to get any bleed from other instruments through it as it takes a direct signal feed to the mixer.

 

 

Active DI's require a power source to operate. If your mixing console has phantom power, this should be placed on the appropriate channel corresponding to the DI box. Most Active DI boxes will have a battery clip allowing a 9V battery to apply power to the DI. If the mixer does not have a phantom power function or a battery clip, there are external phantom power supplies which are available.

 

If you were to have the DVD player out of cable reach of the mixing console, you could use two (one for each audio signal) to take the RCA signals (not all have RCA inputs so you would need a couple of RCA to Jack connectors) to two XLR feeds which could be sent to the desk.

 

Hope this helps B-)

[dmxtothemax]

The passive DI is usually just a transformer,

It has two jobs to do

correctly match the impedance from say a guitar, A guitar will have an impedance of at least 100k.

The input impedance of a balanced microphone input stage will be 600 ohms or less.

So the audio transformer will match 100K ohms to 600 ohms.

 

The second job of the DI is to provide electrical isolation for the balanced line.

So an unbalanced line becomes a balanced line.

 

The balanced system uses low impedance and balancing to reject noise in what is usually a very

noisy electrical enviroment,

remember in a theatre or show enviroment there could be hundreds of amps of lighting and dimming

systems, which will produce considerable EMF.

Which sensitive unbalanced lines could pick up.

 

A passive DI is also useful for connecting I pods, mp3 players or laptop computors to the sound system, which can sometimes be noisy.

 

Hello,

I have a number of DI boxes and I am really not sure how they work or what for. I do not do anything with guitars or whatever. I work at a high school and do stuff with dvd players being connected to the theater sound system. is this something these could be used for?

 

I am just lost really what they are for.

 

thanx

[boatman]

Sorry to hijack this thread, but I need a couple of 1:1 transformers to take a stereo feed of the sound desk output into a Fat Frog, over a 30m cable run. This one might be a suitable candidate, but there's a severe lack of technical detail on the web page.

[KevinE]

The original job of a D.I box (direct injection) was to take a speaker-level signal and put it into a line level input on a desk. This was to make it easy to interface organs, keyboards and guitar amplifiers etc with a mixer before the days of 'line out' sockets, you simply took a pair of wires from the back of the instrument speaker and connected it into the DI box input meaning you didnt have to mic-up the original instrument. The DI box provides isolation because the high speaker level output of an instrument could not itself be relied on to be either isolated nor at a safe voltage to put straight into a mixer.

 

Nowadays DI boxes have variable attenuators meaning they can also be used as plain old signal isolators for line-level or other sources making them a useful tool for many applications, indeed this is their most common application.

 

Passive DI boxes are the oldest (or cheapest) type which contain a double-wound matching transformer but no active electronics/amplifier etc, modern varieties usually have several I/o options eg balanced/unbalanced and selectable attenuation.

Active ones of course are either phantom powered or have a mains adaptor or 9V battery and contain circuitry that corrects for any loading, losses or distortion that a passive box may introduce in certain circumstances.

[TomHoward]

Sorry to hijack this thread, but I need a couple of 1:1 transformers to take a stereo feed of the sound desk output into a Fat Frog, over a 30m cable run. This one might be a suitable candidate, but there's a severe lack of technical detail on the web page.

Completely off-topic, but we bought a Behringer Xenyx 502 to attach to the line input of our Frog - as once a chase is in Bass mode, the 'Step' button doesn't seem to work to over-ride it, so if the feed is lost the chase stops running. The Xenyx gives the lighting operator the ability to adjust the input level to get the chase running effectively without having to disturb the sound bloke, gives them a visual cue that the feed is working, and you can plug a mic in for them to hit if the feed goes down.

[boatman]

Sorry to hijack this thread, but I need a couple of 1:1 transformers to take a stereo feed of the sound desk output into a Fat Frog, over a 30m cable run. This one might be a suitable candidate, but there's a severe lack of technical detail on the web page.

Completely off-topic, but we bought a Behringer Xenyx 502 to attach to the line input of our Frog - as once a chase is in Bass mode, the 'Step' button doesn't seem to work to over-ride it, so if the feed is lost the chase stops running. The Xenyx gives the lighting operator the ability to adjust the input level to get the chase running effectively without having to disturb the sound bloke, gives them a visual cue that the feed is working, and you can plug a mic in for them to hit if the feed goes down.

 

Thanks, that's only a few pounds more than a pair of the interfaces I was looking at, so I think I'll order one.