why is impedance so important?

Posted: Mon Dec 01, 2008 5:21 pm

A buddy of mine let me borrow his Great River Mp2nv and I fell in love with the thing however there is one thing bothering me. When he's tracking a song from his motif xs to protools he always has the impedance switch in. He's tracking everything from kick, snare, guitars, bass, piano pretty much everthing is with the impedance switch on.

Is this a good thing?

Posted: Mon Dec 01, 2008 7:44 pm

I'm assuming the impedance switch is like a pad?
If it is a pad, this works to make the microphone less sensitive so you can run your pre-amp hotter.
Some good quality pre's sound better when driven hard.

Posted: Mon Dec 01, 2008 9:28 pm

The impedance switch on the GR pre-amps selects either 1200 or 300 Ohm as the load impedance on the XLR mic input.

For some microphones (mainly FET-buffered capacitor mics), the switch will have little effect, but the 300 Ohm setting may attenuate relative to the 1200 Ohm.

For many dynamic mics (including ribbons), however, there will be a sonic difference, as the 300 Ohm setting will give a higher damping factor for the coil (or ribbon).

The GR pre-amp also has a switch for loading the output transformer with 600 Ohm. Switching this in runs the transformer much harder, which many engineers like to do for some types of acoustic material.

Posted: Tue Dec 02, 2008 1:53 am

I have the UA 4110, which also features an impedance selector. In addition to the technical explanation above, there is a certain sound that you get (on some mics) by changing this setting. It often gives me the sense that the source can be "roomy" or more "focussed". As usual though, words are poor at describing sound - try it yourself and see!

Posted: Tue Dec 02, 2008 9:26 am

I just hear a boost in mids I dont know if thats good though. I dont really use it for microphones but rather for the DI's.

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