I was first introduced to Crimson Audio Transformers through their useful Mogaine ribbon mic pre-preamp [Tape Op #110]. I later tried one of their modded SM57 mics while I was working back at Treelady Studios in Pittsburgh a few months ago and was really floored with the guitar sound it produced. The session was a three-day marathon, and I didn't have time to look into the mod very much, so I jumped at the opportunity to test all three of Crimson's new SM57/58 modifications.
Crimson offers three different modification flavors in the Mod Squad series: Orange.sm, Yellow.sm, and White.sm. Orange and yellow utilize "tuned" transformers while white includes a transformerless phantom-powered circuit. Each modification comes already mounted in a replacement mic handle, making installation a breeze even for the most technically inept like myself. Simply unscrew the stock handle on your SM57 or SM58 mic, identify the two terminal connections (the leads on the replacements are the same color as the original to make things easier), unsolder the stock connections, and solder the new leads. Screw the mic handle back on, and you're in business. Each modified handle comes marked with a Crimson Audio logo and an appropriately colored XLR insert to distinguish between your originals and the modified mics.
Onto the transformers themselves. I should first note the sheer difference in weight between the original SM57 and the orange and yellow modifications. Both mods were significantly heavier than the original due to Crimson's beefed up transformer designs. According to Crimson, Orange.sm has a double "E" transformer that is 40% larger than the original SM57's, ultimately producing "a bigger bottom and more open upper-mids." On the other hand, Yellow.sm sets out to produce a "more pronounced mid and upper-mid response without being harsh" by employing a twin-coil humbucker design.
In use, I found Crimson's descriptions pretty spot on, though I always worry about possible confirmation bias. To avoid this as best as I could, I set up DI'ed bass and guitar tracks, then re-amped them through identical signal paths, changing only the mics. It was then as simple as soloing between the tracks to hear the differences. I instantly preferred Yellow.sm over the other two options and the stock SM57, for both clean and distorted electric guitars. It was clearer and more articulate than the original, and present without being bright or harsh. Not surprisingly, I favored Orange.sm for both electric bass and kick drum applications, where it offered a subtle, natural bump in the low end. In almost every instance of blind A/B'ing, I chose one of the Crimson mods over stock. To my ears, all three mods exhibited a slight dip in the 300-400 Hz range, in addition to the characteristics mentioned above. This made the recorded material sound closer to done before ever reaching for an EQ. I should also note that these differences were always subtle and remained true to the original character of an SM57. In other words, the modified transformers did not turn the mic into an RE20 or SM7, but instead enhanced the already familiar character.
Now the White.sm handle is different from the other two in that it doesn't include a transformer and instead uses a phantom-powered electronics pack, which brings back the 12-15 dB of signal level that's lost without the transformer. Recordists have been removing SM57 transformers for years, and Tape Op even featured a "how to" on the modification back in issue #52. But again, if you're like me and not prone to disassembling perfectly fine gear, then Crimson's white mod is a quick and easy alternative at an affordable price. Plus, you don't lose the output gain!
I preferred the white modification over the stock mic on both guitars and bass, but it was most remarkable on material heavy in transients, like snare drums. Removing the transformer allows the diaphragm to respond more easily to sound waves, resulting in a faster reaction to sharp transients. I found that White.sm produced a much punchier and more detailed snare sound, which is why it hasn't left the snare since!
As I mentioned, I'm usually not one to tinker with gear that isn't broken. In that way, I feel pretty different from most of my engineer friends. But Crimson's Mod Squad handles are a breeze to install and really do enhance the sound of an SM57. And if it ultimately gets me closer to a finished guitar or snare sound more quickly and without as much EQ, then sign me up.
Also, for those who are scared of soldering or don't want to mod the mics they already own, Crimson's exclusive distributor, Front End Audio, has new SM57 cartridges for sale, and will do the handle soldering for an additional $25 charge.