Intro: DIY "bullet" Style Harmonica Mic!
In this instructable, I'm going to show you how to build your very own "bullet" style harmonica microphone. You will get that cool bullet-mic look with shelling out the 100's of $$$ that you would pay for a real vintage bullet mic. Tone? That all depends on the mic element you choose to put in this shell. This shell has some serious Mojo because anything you make yourself has GOT to have more mojo than something you bought!
This Instructable WILL NOT cover the how-to's of mic element choice, mic wiring, or soldering, although you will need to know all of these things. For info about soldering, search around here, you'll find plenty of instructables on how to solder! (eg: https://www.instructables.com/id/How-to-solder/). For info on mic wiring, see this instructablehttps://www.instructables.com/id/I-Mic-Harmonica-Microphone/ . For more info on mic wiring (including videos) as well as mic element selection, check out my other harmonica microphone instructable https://www.instructables.com/id/How-to-build-your-own-harmonica-mics/.
Let's get started!
Step 1: Get the Parts Together.
Next: You will need the following items to complete this project:
1) A 1 and 1/2 inch diameter "slip on" PVC endcap (from the plumbing section of your local hardware). This will form one half of the mic shell.
2) A 1 and 3/8 inch diameter metal fence post cap (From the garden section of you hardware store). This will form the second half of the mic shell.
3) A package of 1 and 1/2 inch diameter rubber "cups" (for putting under you kitchen table's legs)
4) A 10 to 100 K ohm log taper potentiometer (for the voloume control, you can get these at rat shack)
5) A 1/4 inch mono panel mount guitar jack (again, rat shack)
6) A microphone element of some kind (mine comes from an old AudioTechnica ATR30 microphone I got used at Savers for $3.99. New it will cost around $30. You can use any element you like for this project)
7) Some hookup wire, acid-free solder for electronics, and some electrical tape.
8) Optionally: some cotton balls, spray paint, an old dryer cloth or other piece of cloth, a knob for the volume control.
Watch the first half of this video to hear more detail about the PVC end cap and fence post cap:
Step 2: Salvage a Cool Mic Element! (or Buy a New One)
If you mic element is coming from an already assembled mic, you have to take that other mic apart and get the element out. This will be different for evey mic type, but you'll figure it out. Many times, dynamic mic elements will have an 'acoustic chamber' of some kind attached to them. This will be attached by a screw or a clip. Take this off. Our mic will have it's own acoustic properties, and the stock acoustic chamber will prevent our mic from having it's own character. Plus, this will make the element too long to fit in the shell. :)
Step 3: Drill Some Holes!
Now you have to drill some holes. Take a 1/8th" drill bit and drill some grill holes in the end of the PVC end cap. I laid out a nice concentric ring pattern using a compass. Now check to see if the fence post cap actually fits into the PVC endcap. If it does, you are golden. If not, then you'll have to carve out a bit of material from inside the rim of the PVC endcap. I had to remove about 1/32" all around the inside of the lip of the PVC endcap before my fence post cap would fit properly into it. You'll likely want to sand the end of the end cap after you drilled the holes. This is the business end that you are going to have in your cupped hands all the time, so you want it to me smooth and comfortable. Mine had some embossed letters on it (basically telling the brand and size) which I sanded off to make it perfectly smooth. I first sanded with 80 grit, and then smoothed it 250 grit. Look at the pics and the video from step 1 to get the idea about where to sand.
Next, drill the holes for the 1/4" guitar jack and the potentiometer (volume control) int he metal fence post cap. The hole for the guitar jack will need to be 3/8" in diameter, and the hole for the potentiometer will need to be 1/4" in diameter. So use those two drill bits, or a step drill bit to do these. Look at the picture to see how I laid these out (at angles on opposite sides of the fencepost cap).
Step 4: Wiring and Screwing.
Once you've got them wired, you attach the potentiometer and the 1/4" jack to the metal fence post cap through the holes you drilled. Make sure you wrap the terminal part of the potentiometer with electrical tape, otherwise you'll probably end up shorting the signal leads to the metal chassis, and all you'll hear when you plug it in will be a buzzing sound. Watch the last part of this video to see how to do that:
(PS. Don;t get confused when you see a different mic element in the video from what I'm showing in the pictures. I originally used a different microphone element in this mic, which did not need to be gasketed the way were are doing it here. That was a very cheap element from a crappy karaoke mic. The audio technica one I'm showing you how to put in in this instructable is MUCH better.)
Step 5: Making the Gasket (this Is VERY Important).
Now we must make a gasket for the mic. Why do this? Well, the mic element is too narrow for the shell, and will rattle around if you don't make a gasket to fix it in place, but more importantly, your mic is going to sound really wimpy if the front of the mic element is not AIRTIGHT sealed from the back of the mic element. This is what lets you get great overdriven tone from a tight cup, and also what allows the tone characteristics of the mic shell to come through. The mic gasket seals around the mic element and creates a resonant "acoustic chamber" out of the rest of the mic shell (all the space behind the mic element). This has to be airtight in order to create pressure differentials between the front of the element (where you are playing your harp, and where your cupped hands and mouth are creating another resonant chamber) and the back of the element (which is the resonant chamber created by the mic shell.
Okay, okay. Let me tell you how to do this. This is where we will use one of those rubber feet for putting under table legs. These feet are the right diameter to fit inside the 1 and 1/2 inch PVC end cap part of the shell. All you need to do is cut out the right size hole in one for you mic element to fit into. Luckily, there are some nice rings already stamped into one side of the the rrubber feet that are handy guides for doing this cutting. First, put you mic element on top of the rubber foot to see which ring you should use as a guide (see picture). Then use a utility knife to carefully cut around this ring. You'll want to make the hole just SLIGHTLY larger then the diameter of the mic element. The rubber foot is going to get compressed when we jam it down in the mic shell, and if the fit is too snug around the element, there won't be room for this compression. Don't worry, it'll all be VERY airtight when we're done. Fit the element into the hole you've just carved. See the pictures for how to get it seated properly.
(PS. If you were using a REAL bullet microphone shell, I'd tell you to go to http://www.harpmicgaskets.com and just buy a ready made gasket from them. They work great, and those guys are really nice and will treat you right.)
Step 6: Puttin' It All Together!
Now we have to put it all together, and we will be done! You want to get the gasketed element seated all the way down into the PVC endcap so that the element is as far down as it can go. You'll need to use some sort if slim blunt poking device to get the gasket pushed all the way in. I used the back of bic pen. Take a look at the pic to see how this looks.
An optional step is to cut a small round out of a used dryer sheet, and to put it down into the PVC endcap before you put the element in. It should cover all the grill holes you drilled. This will act like a pop filter, and may help keep spit away from the element too. You can also use fabric. Colored fabric might show through the grill holes, which could be a cool effect.
Another optional step at this time is to pack cotton balls all around the rest of the exposed part of the back of the mic element. This will create a slightly darker tone, and might also help reduce some handling noise. You should experiment with your mic first though to see how it sounds with out the cotton first. It might just sound great without the cotton. If it sounds a little too bright and hollow for you, consider the cotton ball trick.
If you want to paint it, now's the time! I opted only to paint the metal fencepost endcap prtion as I like the look of the black PVC. I used four coats of yellow enamel spray paint formulated to bond to metal and to make a nice smooth glossy finish. You could spray a coat or two of clearcoat or bruch on some clear polyurethane for a glossier finish, but I didn't. Check out the pics of the painted mic below
To do the final assemble, all you do is fit the lip of the metal fencepost cap into the the PVC endcap. If you carved it out right, it should fit nice and snugly. It's best to avoid gluing the two parts together so that it will be possible to get inside it in the future if you should need to fix it or ever want to change out the element. If you are really happy with it though, a little glue will make the connection permanent and very strong (I didn't glue mine). If you have a knob to fit the shaft of the volume potentiometer, go ahead and stick it on now. I didn't have aknob that looked good, so I left the knob bare. I used a knurled shaft potentiometer, so it has plenty of grip all on it's own....
And that's it! No get out there and wail on your new awesome mojo-filled bullet mic!
TIP: If you have used a low-Z element (as I have here), you may find that it sounds a bit wimpy when you plug directly into an amplifier meant for electric guitar. This is because of an impedance mismatch between the mic output and amp input. You can solve this a couple different ways. One is to buy an impedance matching transformer (about $15), and plug the mic into that before the amp. Another is just use a booster pedal. A good cheap one is the Danelectro Fab distortion pedal, which you can also get for $15. Just turn the volume on the pedal all the way up and the distortion all the way down. I go the booster route (with that FAB pedal) because it gives you added control over tone and volume. You can plug a low-Z mic straight into a PA, a "keyboard amp", or an "acoustic guitar amp". If you used a High-Z element, you can plug straight into a guitar amp.
Step 7: Sound Clips!
How does it sound? The following sound clips should give you a clue. All were recorded on my computer with Audacity. The mic was plugged directly into a solid state amp I built. i set the amp on a mild overdrive setting.
Sound clip 1: MS Blues Harp in A playing "Got my Mojo Working"
Sound clip 2: Seydel Soloist Pro in Bb playing a slow blues inspired by the music of Adam Gussow
Sound clip 3" Special 20 in Low E playing a 3rd position jam of my own that uses tongue blocked octaves heavily