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Help fixing Shure SM57 Unidyne III
Old 28th February 2011
Gear Nut

Help fixing Shure SM57 Unidyne III

Hey everyone.

I was hoping that maybe someone has had some experience repairing shure SM57s. I bought a broken one off ebay as a kind of project. It's proving to be a little more difficult than I thought it would be.

I put up what I think are the best pictures I can get, tried to get a variety of angles. Really, where I am stuck now is that there seem to be 4 wires coming out down by the XLR pins, only 3 of which are attached to the XLR connectors (properly) and then there is 1 wire just hangin out with a loose end. I don't think it's supposed to be attached to the 4th XLR tab because it has no signs of solder or of a wire having broken off of it. I can't see up the bottom of the microphone well enough to see what's going on on the bottom side of the transformer. I can sorta see the top of the transformer, but I can't really see any of the joints of the wires going in and out of the transformer. I'd like to remove it and get a look at everything disassembled, but I don't know that that is going to be an option because it's glued in there like cement. I suppose I could saw through it somehow if it came to that with serrated blade of some sort.

When I first got it, it made no sound. There was a wire in the middle chamber that had broken midway along it's length. I exposed clean wire and soldered them back together, and then the microphone picked up noise, but it sounds like a broken speaker where only the tweeter works kinda. No bass and kinda like a talkbox. It doesn't sound distorted. The signal is very very low, much lower than a 57 normally is.

Any ideas on what the deal is with this 4th wire? How to go about getting access to the joints on the transformer.
Attached Thumbnails
Help fixing Shure SM57 Unidyne III-xlr-joints-good-but-1-extra-loose-wire.jpg   Help fixing Shure SM57 Unidyne III-wire-obviously-did-not-come-4th-xlr-connector.jpg   Help fixing Shure SM57 Unidyne III-soldered-broken-wire-together.jpg   Help fixing Shure SM57 Unidyne III-resoldered-yellow-connector.jpg   Help fixing Shure SM57 Unidyne III-cant-see-down-there-much-less-stick-solder-iron.jpg  

Help fixing Shure SM57 Unidyne III-cant-really-see-whats-goin-down-there.jpg   Help fixing Shure SM57 Unidyne III-cant-really-see-whats-goin-down-there-2.jpg   Help fixing Shure SM57 Unidyne III-bar-holding-transformer-cemented-w-glue.jpg  

Last edited by nathanp; 28th February 2011 at 10:44 PM.. Reason: realized I left out something in a sentence
Old 22nd March 2019
Here for the gear

Was wondering if you ever found a fix for this issue. I have a Unidyne 57 with the exact same problem and I’m a bit lost at the moment. Any help is appreciated!
Old 22nd March 2019
Lives for gear
toledo3's Avatar

The reason there are four leads on some older unidyne mics is because there is a high z and a low z 2 is high z. They were setup for four pin cannon connectors. No need to chop the wire off.

If the mic is low level/funny when going into a mic pre, it may be that the high z connection is wired up instead of the low z. Or that the mic is broken.

Here’s the full breakdown from shure’s site:

Wiring of vintage Shure mics: 3 or 4 pin Amphenol to XLR | Knowledge Base | Shure Americas
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