How to Mount a Switchcraft 2501 MP Connector in a Shure Bullet Shell

Required tools:
Drill bits - 19/64, 11/32, and as many sizes in between as you can afford
3/8-32 Tap
Soldering iron

Recommended tools:
Drill Press
Dremel

The Shure 520, 404, and other Bullet shells come stock with a hard-wired cable. Many harp players prefer to have a cable disconnect so the mic can be more easily stored. The most common connector is a Switchcraft 2501 MP. These are available at many Electronic Supply companies like Allied and Mouser. However, drilling and tapping the hole can be a tricky procedure. If you are not comfortable with using power tools, it is probably best to leave this job to a pro.

Making a Mic Jig
Ask any mic builder and they'll tell you the hardest thing about messing with mics is how to hold them. I have tried all sorts of contraptions. Of course, it is completely possible to simply hold the mic in one hand and drill with the other, but this particular job requires a certain amount of precision. I don't recommend trying to drill the mic by hand.

Lately, I've been experimenting with molding a jig specifically for a given mic type. It's cheap and easy. All it requires is some good quality plaster of paris, a short piece of hardwood dowel, and a containment field. I used a plastic cup, but you could use just about anything. If you're able, I'd suggest building a shallow plywood box that you could mount to the drill press. Don't get cheap plaster of paris, as it is too chalky and brittle. You can get the good stuff on line. Look for casting quality. It is also possible to use other stuff, like liquid plastic, etc. if you want to spend the extra money. Even the best plaster of paris is not that great, but will do the job. By the way, if your mic is painted and you don't want to mar the finish, you may want to wrap the painted surface in duct tape or masking tape before beginning this whole process.

Preparing the mic
I cut a 3" piece of 5/16" oak dowel (nice and straight), and sanded it to just more than 19/64 (the size of the cable hole in a 520 shell) and press-fit it into the mic, making sure it was as true as possible.

I mixed some plaster of paris to a dough-like consistency, and pressed the mouth of the mic over the mixture. Not much is needed here, only about 1/4" of depth. All that's necessary is that you cover the mouth of the mic with something. Even Duct tape would do.

Once the mic was prepared, I mounted it in the drill press and covered the mic with a demolding agent. I use a professional silicone demolding product, but most anything slippery will do, including silicone, paste wax, vegetable oil or even Pam. I coated the entire mic, inside and out so the excess plaster would wipe off easily and the mic would demold with very little pressure.

Preparing the Mold
Nothing to this part. I just cut a plastic cup down to around 2-1/2" or so. I mixed a fairly wet batch of plaster, enough to fill the cup about 3/4 full. Then, using the drill press, I plunged the mounted mic into the cup and locked it off for about 5 minutes until the plaster was set (but not completely hardened). I popped the mic out of the mold, sanded the top side (just to make it pretty), and the job was done.


Here's the mic, waiting for the plaster to set (about 5-10 minutes)	The mic removed from the plaster jig

Wiped clean, the mic is now ready to drill. Align the mic to the drill press with an 11/32 bit	Time to drill. Before you do, put on a glove. Use incremental sized bits or (even better) a tapered bit or reamer

Drilling the Mic
This is the trickiest part of the entire job. I suggest wearing a glove for this process to protect your hand. There is a tendency for the standard twist drill bits to "grab" and rip the shell out of your hands or whatever jig you're using. This can cause damage to the shell and leave nasty blood stains on your workbench.

Start with a 19/64" bit and plunge into the cable hole to align the mic and drill press. Switch to the next larger size. The more incremental sized bits you have, the better off you are. NOTE: If you are buying bits, consider getting a few sizes of reamers or tapered bits instead. Reamers are specifically designed for enlarging holes. They have a slight taper will will reduce the problem of grabbing as mentioned above. The final size hole should be done with a standard twist drill however, because the reamer may not reach far enough into the sell to give you the proper sized hole. If you are using the Switchcraft 2501 MP, your final hole should be 11/32. If you need bits and taps for this job, you can find them at McMaster-Carr.

Preparing the Connector
The 2501 MP connector has some splines at the base that are used to press-fit the connector. These will have to be removed. I do this with the lathe, but you can use a Dremel or even a metal file. The brass is soft, and you need only to take off enough material to clear the threads. If you happen to have a 3/8-32 die (I don't), you could instead remove the splines by tapping them, though I haven't tried.

Soldering the Connector
There are several soldering methods that you can use. At the very least, you'll have to solder a wire into the center conductor. Greg Heumann at Blowsmeaway.com has a very good primer on soldering screw-on connectors. It's easiest to do the soldering before you put the screw-on in it's final home. Personally, I like to drill a hole in the connector threads and solder in a ground wire. This method guarantees a good path-to-ground, but compromises the threads, because you'll have to ground that area smooth. That is, unless you have a 3/8-32 die (I think I'll order one).

Tapping the Hole
You'll need a 3/8-32 tap, which is a pretty common size. Since the tap is tapered, it's important to plunge it as true as possible into the shell. Mounting the tap in the drill press and hand-turning the press with the mic resting in the jig can help keep the tap straight. If your plaster of paris jig is not mounted to anything, this will be a three-hand job, because you'll have to use the press's plunger to hold pressure between the tap and the mic.

Is this overkill? Probably. You can easily do the job by hand. Once the hole is tapped, screw in the connector and check the fit. If there is any "lean" to the connector, you can carefully re-tap the hole, creating some side pressure to wallow out the threads. If you are slow and careful, you can take off just enough metal to allow the connector to seat properly without compromising the integrity of the threads.

Seating the Connector
Although there is a hole in the back side of the shell for a set screw, drilling and tapping the shell will remove enough material that you probably won't be able to reuse the set screw. Insead, I will screw the connector in place and drill /tap a hole to fit a 1/4" 4-40 screw. Add a little superglue or loctite to the screw and the job is done.

Are you still here?
If you are, you are hooked. It's hopeless. Get the tools and do the job, it'll be fun. If you've decided this is a job best left to the pros, then there are many guys who will do a fine job for you. I have a few listed in my links section that you can trust. At least now you'll understand why they charge so much to do the job. And whatever they're charging, the job is worth triple!