Balanced versus Unbalanced - When to use a DI Box
Date Posted:21 September 2011
What is a balanced signal?
A balanced signal is when you have 2 copies of the same signal but one is phase reversed. This is used to remove noise from your signal because when the 2 phase reversed signals are switched back in phase, any noise picked up by the cable is phase reversed - effectively cutting in out completely (It's really ingenious when you think about it).
So how do I tell if I should be running balanced or not?
The simple rule is - If you start out with a balanced connection you should try and keep it balanced all the way till it gets to the mixer. Changing to unbalanced at any point makes your signal unbalanced and you will lose the noise cancelling effect (even if you use another lead to go back to balanced)
The basic take home from this is that if you're using a Mic and your connecting to a mixer, always use XLR - XLR (or Cannon to Cannon) cables. don't be tempted to use an XLR - TS Jack at any point.
WARNING - Many PA systems have 1/4" inputs but these are often very low gain - so they suit a loud source like an iPod or a keyboard but are not ideal for microphones. An iPod can have a signal of 1000mV (or 1V) or more whereas a typical microphone is only 20-40mV
Now the main reason you would use an XLR to jack cable is when you have a very short run of cable (up to 20ft/6M is OK) and your plugging into a basic amplifier like a guitar amp or keyboard amp (that doesn't have a balanced input.) In this case, it's completely acceptable to use an unbalanced cable.
What About if I want to connect an unbalanced signal to a balanced signal - Can I just use the cable in reverse?
While this can work you will have a lot of problems. If you do this, you won't get the benefits of a balanced signal. the correct way to connect up an unbalanced source is to use a DI Box. A DI box will take a high impedance unbalanced source and make it Balanced, Low impedance & Louder (if it's active). low impedance means it won't lose as much signal or top-end when sent down a long cable like a snake or multi core. If you have a keyboard with a high output you can connect up to the 1/4" unbalanced inputs without much of a problem - but the pro way to do this is to use a DI box. If you're using a passive bass and you don't use a DI box your sound will be terrible (weak with no top end)
An active DI box is the best type to use, an active DI has a built-in buffer that delivers a stronger signal than the passive counterpart.
What do all the switches do on a DI Box?
(Signal) Earth lift - Sometimes you can get an earth loop. its usually only an issue when you have 2 devices with 2 different power supplies., If you're getting noise, you can consider lifting the earth. If that makes the noise reduce then leave it open, if not switch it back (WARNING NEVER REMOVE THE EARTH FROM A POWER PLUG - IT COULD KILL YOU)
Pad / Attenuation - If you have a loud keyboard or bass amp output (Never connect to a speaker out - only connect to a line out or signal out) you can reduce the signal level so it doesn't distort the input on your mixer, it starts at 0dB (same level) and then goes to -20dB (softer) and finally -40dB (softer again). This is very useful if you have a keyboard with a high output.
Phase - This changes the phase of the source to the mixer, it can be useful if you have feedback issues or any strange phasing problems, but normally it should not be used.
Secret Tip - For a great recorded guitar sound use the shortest cable you have, and remove any unnecessary pedals or cables from your sound.
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