Wiring your mic properly is crucial to get the best performance from it. It is possible to wire a mic improperly and still have it work. It is very important to ground your mic properly to prevent hum. The shell of your mic, if it’s made of metal must be grounded as well. As they come from the factory, the Shure green bullet mic’s have the shell grounded via the tension spring where the cable enters the shell. The shielding from the mic cable (the bare outer wire that wraps around the inner wire(s) of the cable is soldered to the upper part of the tension spring that enters the mic. The spring has a wire (usually gray) that is soldered to the top of the spring as well and it is used as the ground wire to the mic element. This way of grounding is a poor design which usually ends up with frayed ground wires inside the spring which causes the mic to crackle, or stop working completely after a while. If you have a mic that sometimes cut’s out or is noisy when you move the cable around at the mic, this is usually the problem and the mic will need to be rewired.
When wiring a mic, I prefer to strip about 5 inches of the cable end then twist the bare wires together. Then run the wires from the cable up through the spring as far as it will go and then insert it all into the mic shell. I drill a small hole with a 7/64″ drill about 1/4″ deep into one of the 2 nub’s cast into the shell on the inside. I then tap it with a #6 X 32 tpi tap and install a ground lug using a quarter inch #6 x 32 screw. A short sheet metal screw can also be used if you don’t have the tool’s to tap the hole. I then solder the braid from the cable to the ground lug along with a short wire to use to ground the element (and pot) as well. If the mic has a volume pot, I’ll run the wire from the ground lug to the negative side of the volume pot. Grounding the mic in this manner will prevent the shield from fraying inside the spring and provide a much better ground for the mic and shell.
Holding an element with the terminal’s up, and closest to your body, the terminal on the right will always be the negative, or ground terminal. The terminal on the left side will always be the positive terminal. With the 520D elements, you can actually use either one of the two terminals that are on the same side as the positive terminal, but as they come from the factory, the lower terminal is the one used for the positive terminal. If it hasn’t already been removed, there will be a 39K resistor soldered to the positive and the negative terminals of the green bullet mic’s. It is there to roll off some of the high frequencies to make for better speech reproduction. Most harp players prefer to remove the resistor to allow for the higher frequencies. There really is not a big difference with the resistor removed and some people can’t tell much of a difference at all.
Soldering wires to the elements that have plastic bobbin’s must be done very quickly or the bobbin will begin to melt where the terminal enters it. Unless you have a black label CR, or one of the few white label CR’s that has a phenolic bobbin, your’s is plastic. It’s a good idea to use soldering flux on the wire’s and the terminals before making the solder joint. Tinning the end of the wires is a good idea too. This will help to make the solder flow onto the terminal fast and to make a better joint. Do not keep the iron on the terminal’s for more than 2 seconds or the bobbin will begin to melt. If the solder doesn’t take quickly, let it cool off before attempting to solder it again and add some more flux to the parts.
When using a volume pot, you’ll see that it has three terminals. The center terminal will be used for the positive wire coming from the mic cable. The remaining two terminals are used for the positive and negative wires going to the element. Either terminal can be used for the + or the negative side. How you wire it will determine which way the volume control will work. One way will make the volume increase if you turn the shaft in a clockwise direction. Reverse the wires and the pot will work increase volume if you turn it in a counterclockwise direction. Whichever way you wire it, the terminal that you use for the negative side must be grounded to the shell’s ground lug as well as the negative side of the element.
The diagrams below show how the Shure 520D is wired using a standard 1/4″ mono phone jack and an XLR connector as shown on the sheet that comes with the microphone’s. Actually, on the sheet that comes with the mic, the lower terminal is shown as being the positive terminal, but either one of the two that are on the same side can be used as the + terminal. As you can see, the element has two terminals on one side and only one on the other. The 520D is a dual impedance mic, thus the extra terminal on the positive side. The straight up high and low impedance elements have only one terminal on each side.
To wire the mic for low impedance, you will use only the two terminals that are on the left side of the element as shown in the top figure. With an XLR connector, pin 1 is the ground (shield from mic cable), pin 2 is the positive (red wire), and pin 3 would get the black wire from the cable that comes on the Shure 520D. NOTE: Pin 1 and pin 3 should have a metal clip on the pin side that shorts pin’s 1 and 3. If it doesn’t, solder a piece of wire to connect pin’s 1 and 3 to achieve the proper ground. When using an XLR connector wired for high Z with a mic such as a Hohner Blues Blaster or a CAD HM50, pin 1 is used for ground, and pin 3 is used for the positive connection. In this case, do not short pin’s 1 and 3, and make sure that there is no clip shorting these pin’s on the pin side of the connector. Pin # 2 will not be used when wiring for high Z. For high impedance using a standard 1/4″ phone jack, either one of the two terminals on the left side is used as the positive, and the terminal on the right for the negative.
When using a regular high Z guitar cable to wire a mic, you will use the outer braid or cable shielding (bare wires) for the ground, and the single center conductor as the positive conductor. Some cables such as the Planet Waves guitar cables have a cable shield and two center conductors. One is red and one is black. The red wire would be used as the positive conductor. The black wire is connected to the cable shielding, but only at one end. These cables have one end labeled as being shielded. This is the end that you will leave on and cut the other end off to wire into your mic shell. With a cable like this, you can simply solder the shielding to your ground lug inside the shell, and then run the black wire right to the element. Since the shield and the black wire are connected at the other end of the cable, there is no need to use a seperate wire from the ground lug to the element.
The Planet Waves cables are very good cables and are usually priced right around $30 for a 20 foot cable. I have used many of them and would recommend that you get one if you plan on wiring up a mic with a permanent cable. Just be careful to cut off the UNSHIELDED end if you’re going to hard wire your mic. It’s a good idea to use a high quality cable to use for your mic. I have seen some of the cheap cables oxidize on the shielding causing the mic to loose strength. Using a high quality mic cable will help you get all the tone that your mic can deliver and help prevent oxidation problems.