DI boxes question

[samneal]

Okay, let's start this off with letting you guys know I'm new to the forum, and relatively new to sound engineering, although I do sound and lighting at my school, I wouldn't really call this proper "sound engineering"!

 

I've recently started doing sound for a local band, and have a few questions regarding DI boxes:

 

I generally don't worry too much about the settings on the DI box itself but am now curious as to what all the settings actually mean!

 

I'm using the DI boxes to run guitar/bass amps into the mixer to run through PA and I was hoping someone could explain the best settings for this out of the following:

 

1. INSTR/AMP - I think this one is self-explanatory.

2. FLAT/FILTER

3. GND/LIFT

[Shez]

Welcome to the forum Sam.

 

Could you tell us which make / model of DI box you're using? The flat / filter switch could be any number of things but isn't all that common on DI boxes so its exact purpose is likely to be specific to your particular DI.

 

The ground / lift switch is there to enable you to break a ground loop should it occur. A search of the forum will reveal a wealth of information about the causes and effects of ground loops but in a nutshell, a ground loop will usually manifest itself as a low frequency hum / buzz through the PA system. It's usually caused by the keyboard / amp / whatever you're DI-ing being plugged in to a different mains supply to that which feeds the rest of the PA.

[jmaudio]

INSTR/AMP - On the instrument setting, the DI box is expecting a high impedance, low level signal from something like a guitar. On the AMP setting, it would be expecting a low impedance line level input. Lots of things output at this level. Keyboards, CD players, etc.

 

FLAT/FILTER - This is dependent on your DI box, and could be various things. However, I think the most likely explanation, is: This is the EQ applied to the signal. On flat, the signal will pass through unaffected. On FILTER, the DI box will roll off the bass frequencies. Typically this roll off starts at about 80hz, and is fairly steep. Probably in the region of 12dB per octave. In most cases you'll want to leave it on flat.

 

GND/LIFT. A very useful feature on DI boxes. Lots of hum problems can be solved by flicking this switch to the LIFT position. Here, the earth path is interrupted, so ground loops can't be made. It works by not connecting the screen of the unbalanced signal to the screen of the balanced signal.

 

Sure someone will be along to provide a more detailed explanation of what they do. But I hope this helps.

 

Jamie.

[samneal]

Welcome to the forum Sam.

 

Could you tell us which make / model of DI box you're using? The flat / filter switch could be any number of things but isn't all that common on DI boxes so its exact purpose is likely to be specific to your particular DI.

 

The ground / lift switch is there to enable you to break a ground loop should it occur. A search of the forum will reveal a wealth of information about the causes and effects of ground loops but in a nutshell, a ground loop will usually manifest itself as a low frequency hum / buzz through the PA system. It's usually caused by the keyboard / amp / whatever you're DI-ing being plugged in to a different mains supply to that which feeds the rest of the PA.

 

Thanks Shez.

 

I'm currently using a Samson S-direct DI box for my live work, however I used to have a Behringer Ultra-DI DI600P, that I bought when I was first getting started with sound engineering and this particular DI box had a flat / filter switch.

 

INSTR/AMP - On the instrument setting, the DI box is expecting a high impedance, low level signal from something like a guitar. On the AMP setting, it would be expecting a low impedance line level input. Lots of things output at this level. Keyboards, CD players, etc.

 

FLAT/FILTER - This is dependent on your DI box, and could be various things. However, I think the most likely explanation, is: This is the EQ applied to the signal. On flat, the signal will pass through unaffected. On FILTER, the DI box will roll off the bass frequencies. Typically this roll off starts at about 80hz, and is fairly steep. Probably in the region of 12dB per octave. In most cases you'll want to leave it on flat.

 

GND/LIFT. A very useful feature on DI boxes. Lots of hum problems can be solved by flicking this switch to the LIFT position. Here, the earth path is interrupted, so ground loops can't be made. It works by not connecting the screen of the unbalanced signal to the screen of the balanced signal.

 

Sure someone will be along to provide a more detailed explanation of what they do. But I hope this helps.

 

Jamie.

 

Thanks Jamie. Very informative, has definitely helped my understanding :)

[timtheenchanteruk]

INSTR/AMP - On the instrument setting, the DI box is expecting a high impedance, low level signal from something like a guitar. On the AMP setting, it would be expecting a low impedance line level input. Lots of things output at this level. Keyboards, CD players, etc.

 

 

Please dont assume this is correct, there are some DIs (definatly one of the behringers) that can accept a signal from an amp, ie a speaker output, so this switch could equally mean instrument (or line level) or amp level.

[grizzly]

I'm currently using a Samson S-direct DI box for my live work, however I used to have a Behringer Ultra-DI DI600P, that I bought when I was first getting started with sound engineering and this particular DI box had a flat / filter switch.

 

Not wanting to sound mean, but did it occur to you to have a look at the user manuals for the units you mention, as these tell you exactly what each setting does?

 

Samson S direct

Behringer Ultra-DI DI600P

[ramdram]

Samneal, just looked at your profile. It occurs to me that you may find this site useful for your edification.

 

http://www.astralsound.com/equipment_guide.htm

 

If you have the resources I would suggest you print off all the relevant pages and keep in a binder wotever. There is a mass of info on the site which is very easy to understand and given your age you will probably soak it up like a sponge.

 

Anything you don't quite twig first off then the forum will probably help out. A word of caution...some spkr cabs and amps can be very heavy, suggest also you google up some safe handling practices....you really, really do not want a duff back at your age.

 

Sincerely hope this helps.

[samneal]

Samneal, just looked at your profile. It occurs to me that you may find this site useful for your edification.

 

http://www.astralsou...pment_guide.htm

 

If you have the resources I would suggest you print off all the relevant pages and keep in a binder wotever. There is a mass of info on the site which is very easy to understand and given your age you will probably soak it up like a sponge.

 

Anything you don't quite twig first off then the forum will probably help out. A word of caution...some spkr cabs and amps can be very heavy, suggest also you google up some safe handling practices....you really, really do not want a duff back at your age.

 

Sincerely hope this helps.

 

Thanks Ramdram, that website looks great; just what I need to fill the gaps in my knowledge! And very wise words, I shall definitely take a look :)

 

Cheers,

Sam