27 May
2008
27 May
'08
5:50 p.m.
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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