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Old January 11th, 2014, 03:47 PM   #1 (permalink)
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SM57/58 impedance tip

Having read this article

http://www.recordingmag.com/resource...etail/330.html

I bought a wee gizmo that is a male/female XLR connector with a resistor soldered across a couple of pins.

The theory is that the SM57 and 58 were designed for use with desks with an input impedance of about 500 Ohms, whereas most modern desks and preamps are 1500 to 2500 Ohms. The gizmo changes the impedance that the mic "sees" to 500 Ohms. The result?

I did a quick voice test with my 58 into a RNP pre and Pro Tools, comparing the mic with and without the gizmo. The gizmo cleans up the mud and reduces sibilance. It's a cleaner, clearer, richer sound. Much nicer to my ears.

I also got nice tones miking a 63 Super using the gizmo and the 58 with the ball end off (but didn't compare it to the same without the gizmo).

A really cheap way for those of us on a tight budget to get more from a 58/57. I paid $30 for the gizmo but you could easily solder one up if you have a spare XLR adaptor, or solder a resistor into the plug of a mic cable.

It's apparently no use on condenser mics and didn't help with my other dynamics, which are more modern. Might help with other older design dynamics.

Anyone else tried this?

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Old January 11th, 2014, 04:32 PM   #2 (permalink)
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The old magic number was actually 600 Ohms.

All the old stuff I worked with was 600 Ohms and then the engineers realized it was voltages, not current that was the vital part of the signal.

I forget when "Bridging" came into widespread existence, but I'm sure some one here will.

This theory states that an input of a device will be at least 10 times higher than the source load feeding it.

So your typical modern mic has an output impedance of 1,000 Ohms, and the mic pre will have an input impedance of 12-15,000 ohms.

Many higher end mic pres have switchable or variable impedance selection which is a very nice option.

The Gizmo should be great with ribbon mics too, and give it a go on an SM-7.

You can build one of these in a box using a potentiometer so you can tune the mics resonant peak.

This is handy when recording sources like drums, percussion, voice.

As you lower the resonant peak you do begin to roll off high end, but your ear will let you know where you want to set things.

Have fun with your Gizmo.
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Old January 11th, 2014, 04:47 PM   #3 (permalink)
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Yep, 600. A lot of preamps have an impedance switch, definitely opens the sound up a bit. But not in a pleasing way for guitar amp tracking IMO.
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Old January 14th, 2014, 05:27 PM   #4 (permalink)
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Sorry, my bad. I was dashing that off from memory before heading out of town for a funeral. I should have checked the figures. That potentiometer idea sounds good.

I certainly liked the way the loader changed the sound of my 58 on my voice, but haven't tried in it a mix yet or on any other voice. I've never been that keen on the 58 for me. I now use a Heil PR35 for live gigs. Got the 58 when I knew nothing about mics and needed one for stage work. It was the one everyone used so I went with that without doing any research or trying anything else. So I think $30 for the gizmo is worth it if I now get a bit more use out of a mic that wasn't being used any more.

The guitar track I did was low volume and clean. I didn't do an A/B test without the loader or test it on overdriven guitar as I was working on a project and was happy with the sound I was getting. I needed to keep working as I don't get a lot of time in the studio due to family commitments.

@ Rusrant: what didn't you like about the impedance change on guitar? And are you talking about clean sounds, dirt, or both?
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