[LAU] OT: Guitar level- Mic or Line?

[Reuben Martin]

Back on Tuesday 27 May 2008, Simon Williams was like:
> Hello.
>
> I often run the PA system for my CU at uni. So far we've been using
> jack-jack leads to connect guitars to the desk. However, my Dad has
> recently started using jack-XLR leads at my home church and says that
> it's much better.
>
> After a very long conversation and lots of googling (which incidentally
> provides no info at all on the subject), I'm now completely confused.
>
> Are guitars mic or line or what?

Hi-Z Line level. (The output level can vary quite drastically depending on the 
type of pickup though) 

>
> The rationale for using jack-XLR leads and connecting to the mic input
> on the desk is that guitars have mics in them so they are mic level.
> Apparently the battery unit in the guitar doesn't make it line level,
> but I'm not convinced.

A battery is for active pickups. Pickups that don't need batteries are 
passive.

>
> The other thing I don't understand is that if that is the case, why do
> people use DI boxes? A DI box takes a high impedance (line level - I
> think) input and converts it to low impedance output (mic level). If the
> guitar is mic level already then what's the point?

The DI converts a line level (regardless of impedance level) signal to Low-Z 
mic level. The reason for this is that line level signals can't travel long 
distances without degrading, but Low-Z mic level signals can go much much 
further. I wouldn't run a -10 dBu signal much futher than 20 feet. (A +4 dBu 
line level signal can go quite a long distance though) Most sources like 
keyboards are -10 dBu though, and levels on guitars can be all over the 
place.


A DI is used because it can take a wide range of signal levels and change them 
all to a uniform Low-Z mic level signal that can travel a long distance.  
They also usually have a ground lift switch for when your FOH and Stage power 
are sourced to different grounds to prevent ground loops. (The hum you 
sometimes get when plugging in a guitar or keyboard) Some can be placed in 
between a head-amp and cabnet. Some have pad switches. Some are active, some 
are passive. Some are crap. (I'm talking about you, Behringer)

>
> Please, could someone shed some light on this because I'm now very
> confused.
>

I wouldn't recommend plugging into a line jack, or a mic preamp. Both can be 
made to work, and both can be a mess. I would recommend getting DI boxes.

The cheap ones that still work good, are the passive IMP DI boxes made by 
Whirlwind. (~ $40)

I prefer active DI boxes because they have a better frequency response, but 
they cost quite a bit more.

I recommend:

BSS AR-133 - Great for keyboards because of the pad switch

Countryman Type-85 - Great for guitars because they can also go in between the 
amp and cabnet. They're also indestructible.

Anything made by Radial.

-Reuben




> Thanks in advance.
> Simon
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