[Harp-L] re: Line out? direct box? still trying to figure out what's what.

[Greg Heumann <greg@xxxxxxxxxxx>]

> From: "Bruce K Ritter" <Ritterbk@xxxxxxxxxxxxxx>
> Date: March 2, 2010 10:57:09 AM PST
> To: <harp-l@xxxxxxxxxx>
> Subject: [Harp-L] Line out? direct box? still trying to figure out  
> what's what.


Hi, Bruce

Everyone is confused about this stuff, don't worry.

The line-out signal from most amps is high impedance. So is the output  
from typical vintage mics. You would use a "DI Box" to connect these  
straight to the sound board/PA. A DI Box has a 1/4" jack to accept a  
high impedance signal and turns it into a low impedance signal coming  
out an XLR jack - that in turn is connected to the sound board with an  
XLR cable.

By contrast, some times we use a vocal mic like a Shure SM57 or SM58,  
which are low impedance mics -- and we want to connect them to our  
guitar/harp amps. The amps are high impedance. So we use a device  
called an Impedance Matching Transformer. That device takes the low  
impedance signal from the mic's XLR connector and turns it into a high  
impedance signal coming out a 1/4" plug.

In truth - these devices are BOTH impedance matching transformers. In  
fact both kinds can usually be used in either direction. The  
difference is only the sex of the connectors. The thingy we harmonica  
guys call an Impedance Matching Transformer is the one for low-in to  
high-out; the thing the soundguy calls a DI box is for hi-in to low  
out. Sounds guys typically HAVE DI boxes, but not IMT's as we know them.

To add one last bit of complication because I'm sure someone will call  
me on it if I don't mention it - although MOST DI boxes are passive  
and would work in either direction as described above, a few are  
"active" meaning they have powered electronics within. These may or  
may NOT work in the reverse direction.



/Greg

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