DI boxes part 1: What does a DI box do, and when do I need one?

greetings all bruno loose here with GLB productions in this video we're going to discuss what does the DI box do and when do I need one on the table in front of you you can see two di boxes on the left previously reviewed you have the BSS audio a r133 considered by many to be the industry standard for active di boxes and on the right you have the jensen transformer equipped radial JDI direct box considered by many one of the best passive direct boxes that money can buy so first of all let's look at the term di where does this come from and what does it mean the term di box comes from the phrase direct insertion or direct injection and it refers to the process of capturing a signal without the use of a microphone this has many advantages first of all you do not pass the signal through the air so it does not suffer from signal degradation while being transferred you don't have background noise you don't have external interferences within your sound that might cause you problems later or be difficult to remove if you don't want them so that's what di box means direct insertion or direct injection box secondly what does a di do di actually has three functions which we will look at one after another connector matching impedance matching and signal balancing so let's begin with connector matching most of you who play guitar or keyboards know that your instrument outputs on what we call a jack connector in other words you take a typical guitar cable which has plugs like this on the end and you connect them to your guitar if you try and plug your guitar directly into a PA system you will immediately discover that these are not compatible with the XLR connectors that are commonly found on mixers as well as on the wall at your venue so what the DI box does is it has jack connectors on one side where you plug in your guitar or keyboard and on the other side it has an XLR output so you would plug in a normal mic cable here and run that into your wall socket or into your sound reinforcement or recording console so that's the first thing that they do now the second thing that di boxes do is impedance matching impedance is essentially AC resistance resistance to the flow of electrical current now I'm sure we all remember our school physics experiment where we connected a battery to a light bulb current flow through the circuit and the light bulb glowed well an old fashioned incandescent light bulb is basically a resistor it's a coil of wire in a vacuum that when electrical current passes through it some of that current is converted into heat and eventually into light energy when you apply the concept of resistance to an alternating current such as that found in a musical instrument you have the concept of impedance now without getting overly technical it's important to understand that all instruments whether they be guitars or keyboards or Fender Rhodes pianos they have what is called an output impedance in other words it is the electrical resistance of the circuit that is outputting the signal from the instrument this can be either high or low typically instruments such as fender Stratocasters Fender Jazz and precision basses that do not have an onboard preamp in other words there's no battery in the instrument have a relatively high output impedance if you connect this output impedance directly to a mixing console or directly to a recorder you will typically experience high frequency loss and this high frequency loss is due to a miss match of the impedances so one of the things that a DI box does is it provides a relatively high input impedance so that you do not encounter this high frequency loss the radial JDI has an input impedance of one hundred and forty thousand ohms 140 kilo ohms the BSS AR one 33 has an input impedance of 1 million ohms or one mega ohm and this will ensure correct impedance matching between your instrument and the recording or sound reinforcement system so you do not experience this high frequency loss the third thing that a DI box does is signal balancing the difference between an unbalanced and a balanced signal is that an unbalanced signal consists of only two legs you have a hot and a ground a balanced signal consists of three legs you have a positive a negative and a common ground the difference in application between the two signals is that a balanced signal can be transmitted much longer distances without the risk of outside interference or signal degradation and unbalanced signal such as that derived from a passive guitar or bass can typically only be transmitted 5 meters of 15 feet before you run the risk of outside interference hum buzz and in extreme cases picking up local radio broadcasts from taxi companies and even the police force which is not something you want breaking in during your gig balance signals on the other hand can be transmitted many hundreds of meters without the risk of outside interference or signal loss and that is why you need a direct box it converts the high impedance unbalanced signal from your instrument into a low impedance balanced signal that can be transmitted a long distance without suffering from signal degradation now let's move on to the question when do I need a direct box the first situation already touched on is anytime you need to run an unbalanced signal more than five meters or 15 feet you need a direct box because you need to convert that unbalanced signal to a balanced signal in order to avoid the problems of hum and bus typical setup for a DI box would look something like this this diagram incidentally is contained in the excellent user guide that is supplied with the radial JDI direct box thank you Peter Janis and all the wonderful folks at radial you would take your instrument in this case the instrument depicted is an electric bass but it could equally be an acoustic guitar or a keyboard you plug that into the DI box you then have two separate outputs this which is your original signal is connected to your stage amplification in the typical manner this which is your balanced low impedance leg is connected to your sound reinforcement console or indeed to your recording setup this leg here needs to be kept short because typically it is still unbalanced so you would need to keep this under five meters or 15 feet this can be as long as is necessary runs of up to 600 meters are perfectly fine with no issues secondly you need a DI box anytime you are dealing with what are called ground loops now a ground loop manifests itself as a very very low hum or buzz in a PA system typically either 50 or 60 Hertz depending on the type of electricity you have in your local area the cause of a ground loop is unequal ground references within your sound reinforcement system once again the folks at radial have provided us an excellent diagram to illustrate this here you have a keyboard the keyboard is connected to your mixer via a signal cable the mixer is connected to a power point typically at the back of the venue or on one side and the keyboard is connected to a second power point typically on stage or near the front of the venue what most people don't realize is that there is actually a second path connecting the two pieces of equipment and this is the electrical system of the building itself now as you can see because of this connection you actually have a loop of cable now if the ground reference at this point is not the same as the ground reference at this point you have a potential difference and as we all know any potential difference also known as a voltage difference will cause a flow of current within this loop of wire and this manifests itself as a ground loop ground loops can be incredibly loud and they can prevent a show from taking place if they're really loud the function of a DI box in this case is to break the ground connection between the instrument and the sound reinforcement console and this is usually done through the use of an audio transformer now an audio transformer as many of you will know is an iron core with two coils of wire one on either side the key thing to understand about audio transformers is that there is no physical connection between the primary and the secondary coils of the transformer it is what is called a magnetic bridge because of this there is no longer a direct electrical connection here and thus the ground loop which previously was continuous and thus causing a hum is now broken and the system falls silent the best way to deal with this issue is with a DI box containing an audio transformer some people attempt to lift the AC or power ground on one of these components to try and do this this is extremely dangerous because if there is any fault with the system any electrical fault the ground becomes you the operator and this in the past has killed a number of musicians including some rather high-profile ones so that's the second function of the DI box to deal with ground loops so that's our video on what does the DI box do and when do I need to use one in a future video I'm going to be discussing the difference between active and passive di boxes what the correct application is for both types and how they differ in the way that they sound and the way that they interface with your equipment until then this is bruno loose for GLB productions thanks very much for watching see you again soon you

Channel: GLB Productions

Views: 446,880

Rating: 4.9348216 out of 5

Keywords: direct injection, direct insertion, direct input, DI box, Radial, JDI, BSS, AR-133, direct box, Sound reinforcement, PA system, public address, ground loop, impedance, instrument, sound system, mixer, mixing console, Keyboard (Musical Instrument), Bass Guitar (Musical Instrument), Guitar (Musical Instrument)

Id: 2SBGSDKgKHo

Length: 12min 37sec (757 seconds)

Published: Thu Nov 21 2013