Building Your Own Mic

Have Fun, Build One

Building your own harp mic can be a fun and rewarding project, whether you build it from vintage parts, or new parts, but it must be done right if you want the mic to work properly. Whatever type of connector you use, it will need to be grounded to the mic shell to keep hum and noise to a minimum. Your choice of element will need to be properly mounted as well, and should be held securely in place with the proper rubber gasket. This is VERY IMPORTANT as it will provide a good airtight seal around the element and the mic shell to prevent air leakage around the element. Most harp mic elements are pressure actuated, which means that the element needs to be sealed properly for the mic to perform as it was designed. If you don’t use the proper gasket, you will loose response and the mic will not provide the sound that it’s capable of providing


Factory mic gaskets for the old Shure CR and CM elements are not available from the company anymore, but you can still get quality custom made gaskets from, The original owner and I teamed up awhile back and we designed some custom gaskets to be able to use vintage Shure elements in a variety of vintage shells. They also designed gaskets for some of the older crystal elements, and other mics that are impossible to find gaskets for these days. Contact Harpmicgaskets and let them know what you need. If they don’t already have it, they’ll probably be able to make it. Many thanks Tim and Jeff for all your hard work, and for providing a crucial part for us mic builders to use that wouldn’t be available otherwise!

NOTE: Harpmicgaskets is now owned by Jeff Spoor, who has taken over the gasket making, and who is also offering his customers custom mic painting services. Jeff is now using a powder coat process which offers a more durable finish in just about any color. Jeff can be contacted at the same harpmicgasket link above if you need a gasket or a new custom powder coat paint job for your mic. Tell Jeff I sent you!

Using the right gasket also helps to keep mic handling noise to a minimum, so don’t try to make a gasket from a roll of electrical tape, or secure the element with a piece of foam or whatever it is you have in the house. The proper gasket is an important part of a good harp mic that does a lot more than just hold the element in place. A professional harp mic needs a professionally made gasket!

When building a harp mic, it is imperative that you use a rubber gasket that fits whatever element you choose to use in your mic to get the best response from it! Most elements are pressure actuated and need to be sealed both around the element and the shell. If air is able to pass by the element into the shell, the element will not give you all the tone that it’s capable of giving. Most of the popular elements can be fit into almost any shell using stock gaskets, or, stock gaskets that may need to be customized a bit. If you don’t think you can get the proper gasket for your project, contact Jeff at the link above for a custom made gasket. The rubber gasket also helps to reduce handling noise picked up by the element, so don’t skimp on the gasket. It’s one of the most important parts of your mic. Using a rubber gasket is the only way to go. Using tape, or other ways of holding the element in place just won’t work as well. Yes, the mic will work, but it won’t sound anywhere near as good as it could, and hand techniques will not produce the effects that they otherwise would. Rubber gasket, thats it, or loose out! I can’t emphasize this enough. As I mentioned earlier, you may be able to get a custom made gasket at the above link or they may have something that you might be able to use with a little customization. The material they use is very easy to mold and work with, and grinds nicely if you have a grinding wheel to use. Just be extremely carefull if you try this because they doesn’t make any rubber fingers as far as I know!

FIG 1a and FIG 1b
Figure 1a and 1b show an Electro-Voice model 605 shell fitted with a Shure Controlled Magnetic element. The gasket was made using a 1/4 in. thick rubber O ring that was flattened out on the outside and on the inside. It was then glued to the element. It was fitted to seal around the shell front and it is held in place by the casting in the front part of the shell that held the screws for the bracket of the original dynamic element, and the diameter of the back part of the shell. This provided for a good seal around the element and the shell for best response, and I didn’t have to damage the shell should the owner decide to replace the element with an original EV dynamic element in the future.

FIG 2a and FIG 2b
Figure 2a and 2b show an American Microphone Co. shell fitted with a Shure CM element. The gasket I molded from a copy of a stock Green Bullet gasket made for me by Tim Dougherty. I had to cut a notch in the bottom side of the gasket as shown in Fig. 2a so the gasket would go deep enough into the shell to allow the grill to fit. Again, the gasket seals both the element and the shell as shown in Fig. 2b. The grille seats on the front perimeter of the gasket and the gasket was molded at an angle around the diameter to fit the angled shell. It’s very important that any harp mic using pressure actuated elements be sealed around the element and the shell to get the best tone and performance from the mic.


I also recommend using a high quality mic cable too, whether you hardwire it permanently into the mic shell, or use it with whichever type of connector you choose to use. You may not think it will make much of a difference, but it does. Use the best quality cable that you can afford. Cheap cables made with copper alloys I have seen oxidize, which will make your mic sound as if it’s getting weak, when it’s actually the cable causing the problem. High quality cables are made of pure oxygen free copper which won’t oxidize like the cheaper ones will. High impedance mics require unbalanced, single conductor shielded mic cables (sometimes referred to as coax). Regular guitar or other instrument cables are unbalanced cables, but are available in lots of different forms and qualities. One of the better cables that isn’t outrageously priced that I like to use is made by Planet Waves. They are very good quality cables with molded jacks. If you’re hardwiring a mic, you’ll need to cut one of the jack’s off. You will notice that these cables have one end that is shielded and one that is not. If cutting one end off, cut the jack that is not shielded off and make sure that you ground the mic shell properly. There are a few other high quality cables available such as Mogami and Klotz, but they can be very pricey and for the money you won’t notice any difference from the Planet Waves cables.

Low impedance mic’s use balanced cables, which usually have more than a single center wire plus the shield. Unbalanced cables usually have a braided shield, which you use as the ground wire, and a single wire in the center of the cable which is used for the positive connection to the element. There are a number of adaptors, and ways to connect to a cable, some which have drawbacks that go along with the advantages like the adaptors that allow you to use a regular guitar cable that just plugs into the mic. While this is a convenient method, the cables have been known to pull out of these adaptors if you happen to step on the cable, or if a band mate stumbles across your cable and out it comes cutting you off in the middle of a solo!

Personally, I prefer the screw on type connectors using the correct type of screw on cable connector, or the XLR connectors that clip onto the mic’s so they won’t pull out. Whatever you choose to use, build your mic using the correct parts and build it the right way or you may end up with a mic that doesn’t sound half as good as it could.

Grounding and Connector

Your mic shell, if made of metal, should be grounded with the braid, or shield of the mic cable if the cable is permanently attached to the mic. This can be done in a number of ways. I like to drill a hole and tap it for a #6-32TPI screw and use some type of a lug that you will screw onto the shell. Most shells have a nub or two inside the shell that you can drill and tap to do this. Grounding the shell will eliminate problems with hum which you may end up with if you don’t properly ground the shell.

If you plan on installing a screw on button type connector like the older JT30’s used, it should have a solid metal to metal contact with the shell. I’ve seen many of these connectors glued into the shell. This won’t allow for a good electrical contact, and they usually end up falling out eventually or become loose. Avoid glueing if at all possible. If you must glue it into the shell, first solder a ground wire to the body of the connector, on the inside of the collar that goes up into the mic shell. Then run that wire to a ground lug inside the shell to properly ground the shell. Then run a wire from the ground lug to the element’s negative side.

When I install this type of connector, I drill the hole in the mic large enough to tap with the proper size tap so I can screw the connectors into the mic shell tightly making for a good contact between the shell and the connector. Some connectors have a band at the bottom of the threads that you may need to grind off to screw the connector all the way in. If you attempt to install a connector this way, you must be carefull not to grind too much metal from the side of the hole in the mic shell where a set screw is located if it has one. If you do, you may not be able to use the set screw which you should use. I try not to remove any metal from that part of the hole, and just make the hole larger by grinding the metal from the opposite side of the hole to enlarge it enough to tap. If you install the connector this way, it’s not necessary to solder a ground wire to the connector. You can just run the wire from a ground lug inside the shell directly to the element.

Volume Control

If you plan on using a volume control in your mic, it too must be grounded to the shell. That is, the negative tab of the volume pot that should be grounded to the shell. When using a volume pot, make sure that you have the proper value for the type of element that you’re using. For Shure CR and CM’s, I like to use 250K pot’s, or 100K pot’s if no 250K’s are available. You can use up to a 500K pot with these elements if you must, but the 250K’s work best. I prefer to use linear taper pot’s for even and steady control of the volume.

If you’re using a crystal element, I would suggest that you use a volume pot with as high a value as you can find. I prefer to use 5 Meg Ohm’s or higher if possible, but use at least a 2.5 Meg pot for a crystal element. You may have a real hard time finding a pot higher than 5 meg ohm’s in value, but the 5 meg pot’s can usually be found at electronic’s outlets such as Mouser or Allied Electronic’s. These work very well for crystal elements. If you use a low value pot with a crystal, you will loose response, especially in the low end, which is something you don’t want to loose with a crystal since good ones seem to be getting very hard to find these days.

No matter what element you use, if you’re using a volume pot, use a pot that is made with a conductive plastic element. You don’t want to use carbon or graphite pot’s with volume controls. They will work, but will eventually cause problems. The conductive plastic pots are smooth and noise free when operating and won’t oxidize. When connecting a volume pot, the center or + positive lead from either your mic cable or the connector will be soldered to the center tab of the pot. You will use the two side tabs as the + to the element, and the – negative side to the element. Just make sure that the side you use for the negative is grounded to the shell and the shield or negative lead of the mic cable. You can use either side tab of the pot for the positive and negative element leads, but, if you want the pot to operate increasing the volume if you turn the pot shaft in a certain direction, then you must wire the side tabs with the positive and negative leads in a certain way. If you wire the pot in a way that the volume control operates backwards, simply reverse the two side tabs and swap the negative and positive leads at the pot (not the element), and the pot will operate the way you want it to.

Wiring Your Microphone

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.