How To Modify Your Shure SM57
Someone suggested that older Shure microphones sound better because the quality of the transformers was better. Then my friend Dave recommended that I rip out the transformer all together! Since the Shure SM57 is inexpensive, and the changes are relatively simple, I decided to try my first microphone modifications in the summer of 2007.
REPLACE THE STOCK TRANSFORMER
The good folks at Mercenary Audio sold me some TAB Funkenwerk T58 transformers, designed specifically to replace the ones that come in stock 57s and 58s. First I unscrewed the back portion of the mic and de-soldered the contacts from the stock transformer to the microphone element. Then I released the XLR connector at the base and de-soldered it.
The next part was tricky… I had to remove the old transformer from the mic body, which was held in place by some sort of rubbery glue. The folks at Mercenary gave me a hot tip: put the lower body of the mic (not the element!) in a toaster oven for 3-5 minutes. Despite warnings I still managed to burn myself. And some of the glue spilled onto the metal tray. Bummer. That stuff would not come off, rendering it unsuitable for cooking food. But it did break the stock transformer free.
Then I needed to insert the new transformer and attach it so that it wouldn’t bounce around inside. A dot of double stick foam seemed to work pretty well. Now I have to admit this doesn’t form the same acoustical cavity formed by that gooey glue. So the new transformer may not be the only significant change. But since I didn’t seem to have a large supply of industrial glue or the manufacturing setup to apply it without trashing other parts of the mic in the process, I decided the sticky foam dot would suffice.
I used a solder sucker to clean off the residue from the previous wiring. I tinned with some good Kester solder because cheap stuff can sound bad. I attached the XLR to the transformer leads. Then I attached the XLR connector to the base and soldered the other end of the transformer wires to the mic element.
I threaded the body back onto the mic. Except for a little glue residue on the outside of the mic, this modified version didn’t look any different from a stock 57. So I added a personal touch, a red enamel “T” for Transformer to help visually differentiate this mic. I call this mic my Hotrod 57.
I nicknamed the next modification Sawed-Off 57. There were two separate goals here: (1) See if I can improve sonics by removing the transformer, and (2) create a low profile mic that is easier to place in tight spots. This mod turned out to be more difficult than I expected. Removing the back portion of the mic was easy enough, but when I went to attach the chassis of the mic to the drain wire I discovered the chassis wouldn’t take solder. So I left the project and came back to it the next day. I decided to try another approach — physically attach to the mic body using a terminal. I took the chassis out into the garage to find out how difficult it would be to drill a hole in it. Piece of cake! The metal was soft enough to accept a standard wood bit in the drill. So far so good.
I soldered the terminal to the end of the wire. I pushed a machine screw through the hole in the chassis, intending to thread the terminal inside the mic body. But the nut and bolt took up too much room inside, so I moved the whole assembly outside the mic body.
I purposely cut the drain wire short so that it would bare any stress instead of the +/- connections. Having cleaned off the old solder and tinned the terminals to the mic element, I finished the soldering by connecting the positive and negative wires. Then I dropped the sawed-off into a SABRA-SOM SSM-1 shockmount. I would have preferred something smaller, but that’s a different project!
My drummer friend Austin brought his kit into the studio as a favor to me. The Hotrod 57 sounded noticeably better than the stock 57 as a snare mic. And even in the somewhat bulky shockmount, the Sawed-Off 57 fit under the high hat better than the other versions. The Sawed-Off had 15dB less output than the other two — no problem up close on a loud snare. And it sounded really great… significantly better than the stock 57 and the Hotrod 57. That was a pleasant surprise. But I also noticed a lot more sound getting in the Sawed-Off from behind. Perhaps the normal frequency limitation of a stock 57 is also a key design feature for the cardioid pattern. It also seemed very likely that removing the rear chassis of the mic exposed the back side of the element to sound that wouldn’t otherwise get in.
Another friend of mine let me put up a bunch of mikes while he sang and played acoustic guitar. This is when the limitation of the Sawed-Off 57 became obvious. That 15dB loss without the transformer was an absolute deal breaker. I like the No Transformer 57 on loud sources like snare and electric guitar cabs, but the Hotrod 57 for sources that have moderate volume.
The sound leakage into the back of the microphone was the biggest problem with the Sawed-Off version. So I decided to return the mic body to the Transformerless version and paint a yellow “N” on it for No Transformer. Someday I’d like to bend both microphones 90 degrees with the Granelli Audio Labs G5790 so they fit better in tight spots.