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



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

http://www.blowsmeaway.com
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