Build Your Own Blues Harmonica Microphone

This tutorial guides you through building your own tone-filled blues harmonica microphone from easily sourced, inexpensive parts. It sounds great. Total parts cost between $30 and $70. Your labor is free. Assembly time runs 1-3 hours depending on your soldering skills.

The most important aspect of amplified blues harmonica sound is the individual player’s skill. Couple that with a microphone and amplifier, and you might find your own satisfactory tone. It will take a long time to tweak what how you want to sound. Most pros will tell you your acoustic playing should precede any work you do amplified. I agree. But there is still the lure of plugging a mic into an amp and having a wail with your harps.

James Cotton’s acoustic skill was superb, and when he cranked up the amp next to Muddy, it was a whole other world.

Custom and off-the-shelf blues harp microphones are great. They come in all shapes, sizes and vintages. You can find lots of commercial and boutique vendors. Original finish, beat up, powder-coated, chrome, dynamic or crystal, most harp mics share four or five things:

1. Sound capsule, otherwise known as an element
2. Enclosure
3. Cable connector
4. Gasket fitting element to enclosure

The variables of these four or more components are immense. High or low impedance, electrical output, response curves, transformers, enclosure shape. I don’t understand half of the options, but with some experimentation, you can take the basic parts and build a working microphone with relative ease.

Finding the individual parts is pretty easy, if you know where to look. I’m gonna show your where they hide, and how to put them together. We’re going to assemble this mic with inexpensive parts, so you can experiment a lot without breaking the bank.

No matter what you wrap it in, the single most-important part of the microphone we’re making is the element, often called a capsule or cartridge. Lots of choices out there. We’re looking for small and inexpensive.

One of the most-recommended retail microphones for starting-out harp players is a Shure SM57 or 58. It’s got a narrow, low impedance dynamic capsule inside. Because it’s one of the more popular mics in the world, many companies make replacement elements for them, and that makes them cheap. Though going straight into an amplifier, high impedance microphones are preferred, we will use a transformer to get the low impedance to high.

I tested a pile of elements, 30 or so that I could get on eBay for $10 or less. There are more than you can shake a stick at. Most of these are manufactured overseas, primarily China. There are also similar knock-offs for Sennheiser, Audio-Technica, and AKG. Most of the ones I experimented with were Shure clones.

There are literally thousands of things you can use as your microphone enclosure. Tin cans, pepper shakers, tea strainers. You name it, someone’s made a microphone out of it. Of course you can use a nice vintage shell like the common Shure green bullet, or an Astatic JT-30. If you find one at a reasonable price, by all means use that. But we’re going cheap, so we’re using one of the most popular options available. It’s a motorcycle turn signal light. Greg Heumann from Blows Me Away Productions was the first builder I know that used a motorcycle tail light as a microphone shell.

This shell is often a little small in diameter for some players but builders around the world are using it. As an alternative, there’s a larger diameter tail light that works well too, but finding or building the right gasket is a bit more trouble. Our primary shell fits the element pretty well, and you can buy a proper gasket online.

After playing each of the many elements, I slowly whittled the best-sounding elements down to 6. Building all six out, I then brought them to the New England Harmonica Intensive seminar, where I let all the players who cared to, try out the 6. There were 15 or so testers, including seasoned pros Annie Raines and Ronnie Shellist.

We used a stock Fender Blues Jr. as the amp in the tests. Not regarded as the best harp amp out there, but certainly available worldwide. After grading the microphones over a weekend, players evaluated two of the elements as standing out from the rest.

PARTS:

• Microphone capsule (element) ($3-15)
• Enclosure ($8-12)
• Cable connector ($6)
• Gasket or plumber’s putty ($3-8)
• 1″ foam ($1)
• Audio Transformer ($7)
• 22 Gauge Insulated Braided Wire ($5)
• Solder – Glue or silicone caulking (optional, $3)
• Shrink Tubing (optional ($2)
• Guitar Cable Adapter (optional, $9)

TOOLS:

• Wirecutter
• Hacksaw or Dremel Cutting Tool
• Good Soldering Iron with small tip
• Pliers
• Small Phillips Screwdriver
• Wire Stripper (optional) or Xacto knife
• Glue Gun (optional
• 5/8 x 32 Metal Tap (optional)

Unscrew the shell grill and twist to remove. Might take a little work, cause there is a rubber gasket inside. Try not to break it. Open up the shell and you’ll see the lens and bulb assembly, attached to two or three wires. Cut them all and remove bulb assembly. Pull out the wires from the neck.

The thread of the stock enclosure is very coarse. But the connector threads we’re going to install are small. If you can, use a 3/8″ x 32 tap in the neck to match up with the threads of the cable connector. It won’t be perfect, but the cable connector will be easier to install later on.

You'll notice that the connector has some flutes at the top of the threads. Still works just fine, but you may want to grind away a bit of the shell neck so the flutes aren't visible when it's threaded into the shell. Just a more finished look.

On this connector, the center hole is the positive connection, and the outside is the negative (ground) connection. Start with the negative connection. It’s a tricky soldering task because the inside of the connector is very smooth. If you’ve got a Dremel tool with a rotary cutting bit, or a triangular pin file, you can grind a small groove inside the connector to better set the wire when soldering. I use black wire for the negative connection, and red wire for the positive.

Cut about 5″ length of wire, and strip about 1/8″ off the tip of each wire. Solder the black wire to the interior side of the connector, and red wire through the center hole. To keep these connections from coming loose, you can fill the connector with either hot glue, or silicone caulk.

Insert the wires into the neck of the shell, and screw in the connector. It will fit nicely if you tapped the shell first, but you can force twist the connector in as an alternative. I apply a little hot glue, or thread-lock liquid on the connector to make sure it doesn’t loosen after time.

Most of the available elements have some sort of housing on the rear to fit various microphones. Generally these are simply hollow plastic or rubber extensions to the element capsule.

We need to remove the excess parts so the element will fit inside our shell. You can use a hacksaw, coping saw, or Dremel cutting disk for this job. Make the back of the element chassis smooth and level if you can.

Be careful with the wires inside the element housing. They can be used to connect to the transformer in the next step.

Almost all of these elements are low impedance, usually 600 ohms. These play great straight through a PA system, but are less desirable for cabling to an amp. On an amp you want a reading of 1000 or more ohms. To convert the low to high, you need an “impedance matching transformer.”

There are transformers you can attach to your microphone cable, but we want to keep this in the shell, so it needs to be small. In our build we will use one available from Shure, but don’t worry, it’s still cheap. $7 from Full Compass Systems. Shure 51A312

Wiring

Here’s your delicate soldering task. These wires are tiny, 22 gauge, and are easily broken, especially when stripping the ends. So be careful.

The transformer has 5 wires. You’ll only be using 4 of the five. Each wire is a different color. Two wires go to the cable connector, and 2 wires go to the element. You can choose to use shrink tubing or electrical tape over the solder points. The tubing works better.

These wiring instructions came from the late Dave Scudamore, who was a great harp mic builder in Chicago. Here are his recommended connections:
1. Transformer Red wire soldered to positive (red) wire of the connector.
2. Transformer Black wire soldered to negative (black) wire of the connector.
3. Transformer Green wire soldered to the positive connection on the element
4. Transformer Yellow wire soldered to the negative connection on the element (see option for Orange wire below)
5. Clip and insulate the orange wire.

(According to Scudamore’s instructions, you will hear a difference in your sound depending on using the Yellow or Orange wire as the negative contact of the element. He suggested you try both, and see which one you like better. He said the yellow usually sounds best.)

Though you don’t need to secure the transformer, you may find a hot glue gun handy here. I glue the transformer to the element before soldering the wires to the the contacts. When I’m done soldering, I use the glue to cover the contact points and wires. This will keep the fragile wires from breaking off during playing or rough handling of the microphone.

The final soldering is the red and black wires from the transformer to the red and black wires leading from the connector.

This has always been a failure point in microphone building. For best results, the element has to be both sealed tightly to the shell, and isolated from vibration when in use.

You have a couple choices here. You can either use a custom rubber gasket, simple plumbers putty, or thin foam rubber to set the element into the shell. I found a roll of foam shelf liner that is just the right thickness.

By all means try the plumbers putty, or foam rubber, but you can get the proper-fitting gasket from Jeffrey Spoor here: https://jlspoor.com/t/harmonica-microphone-gasket...

If you have one handy, use a small bit of breathable foam inside the grill, which will stop some of the breath and popping noise the element will pick up without some cover. I found very cheap microphone wind screen foam on Amazon.

Press the grill back on and align the screw hole at the bottom. This may take some effort, as there is a silicone o-ring on the shell fitting, but be careful to avoid damaging the face of the element.

The connector we’ve used is a traditional Switchcraft screw-on connector. Microphone cables to attach directly to this connecter are readily available. If you want to use a standard 1/4″ guitar cable, you can get an adapter between the screw-on and the 1/4″ plug. The model is a Switchcraft 332A. Even if you use a screw-on cable, it’s handy to have the adapter around in case the cable fails. Then you can just use a guitar cord.

Microphone capsules:
Here is the most popular element from my tests:
2x Replacement Cartridge Fit For Shure Beta 58A Microphone Repair Parts #VD10 CH

Try some of these searches on eBay for and you’ll get plenty to choose from.
“shure replacement microphone capsule”
“replacement microphone capsule”
“dynamic microphone cartridge”

Shell Enclosure
Search eBay for “bullet tail light.” Many of the bullet lights have the same interior diameter.

Cable connector:
Switchcraft 2501 available at Digi-Key and Mouser electronic supply houses

Gasket
C-Note model, jlspoor.com

Plumber’s putty:
Any hardware store

1/8″ thick acoustic foam
Search eBay or Amazon for “microphone wind screen.”

Link Impedance Matching Transformer
Shure 51A312 Impedance Matching Transformer at Full Compass

22 Gauge Insulated Braided Wire:
Any electronics Store.

Glue or Silicone Caulking
Any hardware store

1/16″ Shrink Tubing
Available at Digi-Key and Mouser electronic supply houses Link

Guitar Cable Adapter:
Switchcraft 332AX at Full Compass