replacing transformer in a Shure SM57

[antichef]

OK - last night I was able to complete the transformer swap for my SM57, so that it now uses the AMI TAB-Funkenwerk T-58 transformer. I've got some samples, but I'll post those on the thread in the microphone forum:

http://homerecording.com/bbs/showthread.php?t=273292

This thread is about the process of the mod -- I took pictures.

First, I unscrewed the SM57 at the middle joint, and also pulled out the XLR pin assembly (by loosening the locking screw in the body of the mic, and gently pulling the assembly free by grabbing one of the pins with needle-nosed pliers). Next to it in the picture below is the T58 transformer, with the XLR-side leads sitting in a disposable drinking straw (more on that in a minute)

As you may know, the body of the SM57 that you see has a large chamber at the top in which the transformer sits, suspended in a bunch of what I think is rubber latex compound, that is solid at room temperature, but softens and liquefies as it heats up.

I *thought* that what I would do is to heat up the mic body enough to soften, but not liquefy the latex, slork-pull out the stock transformer, then jam the drinking straw (I pinch-sealed/cauterized the bottom of it with my soldering iron after taking this picture) down through the gooey latex and out the bottom of the mic, then pull out the drinking straw, leaving the leads from the transformer sticking neatly and cleanly out the bottom. Cool idea, huh? Turns out the straw was too big to fit through the hole at the bottom of the chamber in the mic body, and I misjudged the heating time, anyway (more later):



I desoldered the leads of the existing transformer from the capsule and the XLR pins. The bottom of the capsule had a convenient indicator of which terminal was positive -- I didn't see that in another SM57 I have. Here's the desoldered mic from the top, where you can see the capsule-side leads sticking up out of the latex goo, and you can see the stock transformer in the goo beneath:



Next comes the culinary step. I took a sock (a *clean* sock) and wrapped it around the top part of the body of the mic, then clamped some vice grips around the sock. The sock was both to protect the mic from scratches from the vice grips, and to provide some heat insulation. Next, I dipped the bottom of the mic in a pot of boiling water (being fairly careful to keep the sock above and out of the water -- if it got wet, then it's heat insulation properties would be lost, and I'd have to use an oven mitt to pick up the vice grips - didn't happen - sock stayed dry):



I don't have pictures of the next step, because it was so timing-critical and I needed both hands. The "right" way to do this would probably be to heat the mic until the latex completely liquefied (and hope it doesn't leak out the hole in the bottom, I guess - didn't think that through, because of my alternative plan), then pour off the liquid in a temporary container (keeping it hot), swap the transformers, then pour back in the latex and let it harden around the new transformer. Typing just now, I'm not 100% sure why I didn't take that approach, except that I was short on time and trying to find short cuts. As I mentioned, my plan was to work with semi-solid latex and real quick swap the transformers using the straw. The first failure occurred when I pulled the old transformer out -- the latex was not quite hot enough to release the transformer, but was hot enough to leave the mic body, so the whole mass came out, still encasing the transformer, but leaving some liquidy stuff behind, which probably began seeping out the small hole where the XLR-side leads go. The second failure came when I tried to jam the straw down through the small hole (in order to avoid the liquid latex traces getting on the wire leads), and found that the diameter of the straw was too big to fit through the hole. I wound up discarding the straw and carefully dangling the XLR-side leads of the T58 transformer through the small hole and out the bottom, then manually separating and pulling off the semi-solid latex from the old transformer, fitting around the body of the T58 in the body of the mic, and reheating to soften it some more. Here's the view from the top of the mic body afterward:



A little rough, but good encapsulation and isolation of the transformer, so it all worked out.

Next, you have to dry off the mic body, of course. I used a paper towel. Here's a vanity shot of the dry mic body next to the now-removed stock transformer, which still has a little bit of latex on it:



Next came the relatively straightforward job of hooking up the leads of the T58 to the capsule and the XLR pins, following Oliver's instructions for the pin-out at:

http://www.tab-funkenwerk.com/sitebu...s/t58specs.pdf

I was fresh out of flame-proof paper towels and used the regular kind (same one I used to dry the mic body) to keep me from burning my cloth towel (did I mention that I have no idea what I'm doing, and I'm basically just a bozo with a cheap soldering iron and an internet connection? ) Don't try this at home, even though you can see here that I did. There was no fire. I used silver-solder for the new connections, and had done my best to remove all the old solder using a solder sucker.



Finally comes reassembly, and then the most vexing problem of all: How are you gonna tell this modded mic apart from your other garden-variety SM57s without disassembling it? I choose embossed tape:



And there you have it -- sound samples will be in the mic forum.

[timthetortoise]

Cool stuff. How much $$$ did the new tranny run you?

[antichef]

Originally Posted by timthetortoise

Cool stuff. How much $$$ did the new tranny run you?

PM'ed you...

[dialatron]

Is it possible to use different transformers in this mod !!!! If so what would you recommend ?

[antichef]

Originally Posted by dialatron

Is it possible to use different transformers in this mod !!!! If so what would you recommend ?

Not sure which one - I looked at the Lundahl catalog and saw one that was 1:5, but it was PCB mounted. The T58 rocks, though! The modded mic almost never goes back in the "locker"

[dialatron]

Can't seem to find the transformer for sale on its own, only as a finished new product mic with transformer fitted. I have a 57 so am looking for the transformer only.Any ideas on where to obtain one ?

[dialatron]

Can't seem to find the transformer for sale on its own, only as a finished new product mic with transformer fitted. I have a 57 so am looking for the transformer only.Any ideas on where to obtain one ?

[jelaci aman]

Originally Posted by dialatron

Can't seem to find the transformer for sale on its own, only as a finished new product mic with transformer fitted. I have a 57 so am looking for the transformer only.Any ideas on where to obtain one ?

http://www.mercenary.com/tatrmosmands.html

"The AMI T58 microphone output transformer was developed as a high resolution transformer upgrade for existing SM-57 or SM-58 microphones to give the same solid character without restricting upper mid and high end response. It effectively makes the mic closer to that of an SM-7."

Good luck! I plan to add the transformer to a XM8500...if it works...

[stevieb]

$75 for just the TRANSFORMER?? Used SM57's often sell for that, or less.

[Chili]

Originally Posted by stevieb

$75 for just the TRANSFORMER?? Used SM57's often sell for that, or less.

It's not meant as a replacement xformer, but one that changes the character of the mic.

Someday, I will do this mod for my 58.