Most DIY enthusiasts who are interested in audio gear are familiar with the standard “tin can mic” (or variations thereof), in which a piezo disc is taped onto the bottom of a tin can and then plugged into a high impedance voltage amplifier, like a guitar amp. These types of microphones are nice because they are so easy to make, but they are quite limited in most other areas, including bandwidth, microphonics, signal to noise ratio, impedance matching, and cable driving. These issues usually result in a very noisy and brittle sounding microphone. So out of frustration with these limitations, we created the “New and Improved Tin Can Mic” -- the standard tin can mic taken to the next level! Using common household items along with a simple circuit, this mic has a tonality similar to the original tin can mic (for all you Tom Waits fans), but improves upon nearly every other feature. The heart of the mic is the Cortado contact microphone which consists of a tiny phantom powered circuit which creates a balanced output from a piezo disc. This circuit provides a high impedance to the piezo disc, but also provides a low output impedance to match a mixing console input. By properly matching the input and output impedances we achieve a much wider bandwidth than the original tin can mic. The fact that the output is balanced provides a very high signal to noise ratio, and it allows for a long microphone cable to be used without signal degradation.
Another improvement we've made to the standard can mic is that we've added a styrofoam cup as a mechanical resonator. The cup floats inside of the tin can via rubber bands, which helps keep microphonics and feedback (in live performance situations) manageable. Another benefit of using a floating mechanical resonator is that it's easy to mod the mic to change its tonality. We can easily alter the resonant frequency of the mic by changing the mass of the cup, or we can emphasize a higher resonant harmonic by adding a vibration node to the cup.
The Cortado contact mic in itself is capable of a very wide, flat bandwidth which is suitable for use as a contact mic in lots of recording situations, on anything from a piano soundboard to a plate reverb. The circuit is fairly simple and can be built from common parts using the schematic given in this Instructable. As a service to the DIYer, the Cortado is offered as a kit from Zeppelin Design Labs. The kit includes the circuit board as well as all the other parts (including matched FETs) to make the Cortado into a variety of configurations for different applications. For this instructable, we will document the construction of the Cortado kit for its application in the “New and Improved Tin Can Mic.”
Every track in this song was recorded with only the Cortado contact mic. The vocals were recorded using the Cortado configured as the "New and Improved Tin Can Mic" described in this Instructable. For those interested, the band in this recording is Ami Moss and the Unfortunate. Recording notes and more info can be found here.
- Tin (steel) can (typical #1 can)
- Styrofoam cup (12 oz)
- 3 rubber bands (medium sized)
- 5” cross stitch or embroidery ring
- #6-32 2” Machine Screw
- 2x #6-32 Nut
- #6 Lock washer
- 3/8” 16tpi nut
- Mic stand adapter with 3/8” 16tpi threaded shaft
- Cortado Contact Mic kit (or these parts):
- Piezo disc (with 6” 30awg wire leads)
- PCB (or bread board)
- 1x male XLR jack with 12” balanced mic cable
- 2x matched 2N3819 FETs
- 1x unmatched 2N3819 FET
- 4x 3.3M 1/4W 5% resistors
- 3x 150 ohm 1/4W 1% resistors
- 1x 1.5K 1/4W 5% resistor
- 3x 220pF film capacitors
- 4” 22awg black ground wire
- ~1sq”double stick tape
- 12 mm nylon standoff
- 2x M3x6mm screws
- Rubber grommet (big enough for the mic cable)
1x Zip tie
- soldering iron
- digital multimeter
- drill bits (9/64, 3/8)
- sandpaper (~150 grit)
- needle nose pliers
- wire strippers
- #2 Philips screwdriver
- can opener (that can remove the top rim of a can)
- diagonal cutters or wire snips
- X-acto knife or razor blade
- Fine tip permanent marker
- Center punch or sharp nail for marking holes through the template
- Solder, 60/40 rosin core, the smaller diameter the better
- Black nylon stockings
- Sticky tack (the stuff you use to hang posters on the wall)
- Tape (masking or Scotch)
- Rubbing alcohol or Isopropyl alcohol
- Small rag or paper towel
Step 1: The Cup
- With your X-acto knife or razor blade cut off the top rim of the 12 oz styrofoam cup. Try to make the cut as smooth as possible. Set the rim aside until later(1).
- The next step creates a cup that is 2 11/32” tall. There are probably several ways to do this but here's how we did it. Use your ruler to measure 2 11/32” (or 6cm) from the bottom of the cup and mark the cup(2). Rotate the cup a few degrees and repeat this step. Continue marking small dashed lines until you make your way all around the cup(3). Connect all the dashes with a solid line(4). Use your X-acto knife or razor blade to cut the cup at this line(5). Set this cup aside until later.
Step 2: The Electronics
This circuit used in the Cortado was designed by Alex Rice who used it for his contact mic hydrophone. We have taken his circuit topology and tweaked a few component values to suit our purposes. In this Instructable we will show you how to assemble the Cortado kit from Zeppelin Design Labs. If you don't have the kit, you can follow the Cortado schematic to assemble the circuit on a breadboard.
Your work space should be well-lit, well-ventilated, and disposable; that is, don’t work on the nice dining room table! Work on a utility surface that you can burn, drill and scratch. A piece of ¼” tempered masonite, or a chunk of MDF, makes an excellent cover if you don’t have a utility work bench.
CAUTION: Solder fumes are not healthy for you. The fumes consist of vaporized flux, which can irritate your nose, lungs, and even your skin. You MUST work in a space where the air drifts away from you as you work, so fumes do not rise straight onto your face.
CAUTION: Solder residue usually contains lead, which is poisonous if you ingest it. Do not breathe the fumes, do not eat the supplies, wash your hands after you handle solder, and sweep and wipe up your work space after EVERY USE.
The printed circuit board (PCB) holds the components in this circuit. All of the components will be installed on the “component side” of the board, which is the side that has the part numbers on it. The other side of the board is called the “solder side”, which, as the name implies, is the side on which the legs of the components are soldered to the board. Proper technique for installing and soldering components to a circuit board is demonstrated in this instructable, but there are several other great resources on Instructables and YouTube under the search “soldering tutorial.” The general procedure consists of the following:
- Install the part on the “component side” of the board, by threading the wire leads through the appropriate holes in the board. For your convenience, the board has silk screen outlines indicating where the components should be placed, along with text indicating the part number and the component value.
- Hold the component in place with your finger and turn the board over.
- Gently bend the leads out at about 45 degrees to keep the component from falling out of its holes.
- Install all of one type of component, bending each of the leads as they are installed.
- Flip the board over solder-side-up, and solder all of the components in one pass.
- Clip the leads off (with small diagonal cutters) right at the solder joint.
- Resistors: The value of resistors are given by a series of colored stripes on their body. There are several tutorials online describing how to decode these stripes, but we will identify each resistor for you by simply naming the stripe colors, and giving you the value and the part number. “Figure 1: Component Values and Locations” is a good reference. If you are colorblind or can’t see the stripes clearly, then you must use your digital multimeter to measure the resistance of each resistor.
Resistors are not polarized, meaning they can be installed in their holes either direction. It doesn't matter which lead goes in what hole.
The hole spacing of most of the resistors on the circuit board allows the leads to be (gently) bent 90 degrees at the body of the resistor(6). This allows most resistors to slip into their holes very easily. Resistors R4 & R8 are exceptions to the normal hole spacing. Notice the picture of how those two components are bent(7).
- Start with the 3.3M resistors (R1, R2, R6, R7), labeled ORANGE, ORANGE, GREEN, GOLD. Find their locations on the circuit board and install and bend the leads as described above(8). Don’t solder any of them until all 8 resistors are installed; just bend the leads to keep them in their place
- Continue with the 150 ohm (150R) resistors (R3, R4, R5). The body of these resistors are blue and are labeled BROWN, GREEN, BLACK, BLACK, BROWN. R4 stands upright on the PCB so bend one lead nearly parallel with its body and install it standing up(9). Bend the leads on the back so it won't fall out.
- Continue with the 1.5K (or1K5) resistor (R8), labeled BROWN, GREEN, RED, GOLD. R8 also stands upright on the PCB.
- You should have a whole forest of bent leads coming out the solder side of the board. Now you can turn the board solder-side-up and solder each one to the board. Use a clamp or vise if you have one; it makes soldering much easier(10,11).
- Now clip each lead with your diagonal cutters at the solder joint. Keep the leads you cut off in a safe place because you'll use some of them in a later step(12).
- Before installing any more components on the circuit board, double check the resistance values of each of the installed resistors. Set your digital multimeter to the “ohms” or “resistance” setting, and measure across all of the resistors. Compare the measured value to the listed value in Figure 1. Make sure they are all correct (within 5%) before moving on!
Place all three capacitors (C1, C2, C3) in their holes and bend the leads on the back(13,14). Turn the board over, solder and clip the leads(15).
FETs are quite sensitive to static electricity and could easily be damaged if they are exposed to moderately high voltages. The voltage rating of these FETs is only 25V, meaning that if over 25 volts is applied across two leads, the FET will likely be damaged beyond use. Unfortunately, most of us are not sensitive to static electricity at such low levels; in fact, most people can't even feel a static discharge less than 1000 volts! So it is very easy to damage these components without even knowing it. Consequently, it is important to handle these components as little as possible. When you do have to handle them make sure you are grounded, preferably by touching something grounded to the mains like the metal chassis of a plugged in amplifier or a refrigerator. At the very least you should touch a large conductive object like a metal desk or a filing cabinet. With this information in mind please proceed carefully.
Transistors are polarized, meaning it is important which way they fit into the holes. The component side of the circuit board has a silk screened outline of the the transistor body in the correct orientation.
Place the silver-painted FETs in the locations of Q1 and Q2. Either silver FET can be Q1 or Q2; it doesn't matter which one goes in those locations as long as they are both silver (16,17). Note the flat sides of Q1 and Q2 face in opposite directions(18). Before you put the transistors in, bend the outside leads out a little so that the leads can fit into the holes on the PCB. On the bottom of the board bend the leads a bit so they won't fall out of their holes. Place the other FET in the Q3 location(19). Please be mindful of the correct orientation. Bend the leads of Q3 on the bottom of the board. Turn the board over, solder and clip all the transistor leads(20,21,22).
Step 3: The Piezo Disc
This step consists of placing the piezo disc on the styrofoam cup and then soldering the leads to the circuit board.
- Clean all the finger oil and other contaminants from the bottom of the piezo disc with rubbing alcohol and a rag or paper towel(30). Use the same rag to clean the bottom inside of the styrofoam cup(31). Make sure you don't touch any of the surfaces you just cleaned!
- Stick the double sided tape to the the bottom of the piezo disc(32,33). Make sure it covers the entire bottom surface. Trim off the overhanging excess with scissors(34,35).
- Twist the wires of the disc together(36). They don't have to be tight, just enough to keep them together.
- Strip off about 1/8” of insulation from each of the two wires(37,38).
- With your X-acto knife make a small hole in the side of the cup, near the bottom, big enough for the piezo disc wires to fit through(39).
- Peel the backing off the double sided tape(40). Place the wires through the hole in the cup form the inside out. Stick the piezo disc to the bottom of the inside of the cup(41,42). Make sure it is well-centered on the bottom.
- Solder the two wires to the PZ1 and PZ2 holes on the circuit board(43). It doesn't matter which wire goes into which hole.
Step 4: The Can
- With your can opener, cut the top rim of the can off(44,45). The top of the can will be very sharp -- don't cut yourself.
- Print out this template. Make sure you print it “full size.” Place the can top-down on the can template(46). Use your marker to mark the 6 evenly spaced solid lines on the edge of the can(47).
- With the can top down on the table, use your ruler to measure 7/8" up from each of the 6 marks. Mark that spot on the can and use your center punch or a sharp object (like a nail) to make a dimple in the can for drilling(48,49).
- Use a 9/64th bit to drill all 6 holes(50). Use a file or a larger drill bit to deburr the holes on the inside of the can.
- Cut the can template out along the dotted line(51). Hold the template in place on the bottom of the can and use your punch or nail to mark the center of the can and the standoff hole(52,53). Also use the template to mark the grommet hole on the side of the can. This is indicated on the template by the straight dotted line coming from the center. Use your marker to draw a line on the side of the can where the dotted line is leading to(54). Punch a mark on the side of the can 1/2” down on this line(55).
- Drill the two holes in the bottom of the can and one on the side with a 9/64” bit(56,57,58, 59). Use a 3/8” bit to finish drilling the hole in the side(60).
- The inside of the can may be coated with something to keep the food that was inside sanitary. You need to scrape some of this off in order to solder a ground wire to the inside of the can. Use your X-acto knife or some sandpaper to scrape the coating off the inside of the can about 1/2” up from the bottom on the opposite side from the 3/8” hole(61). The scraped area needs to be no larger than ¼ sq in. Once it is scraped or sanded thoroughly, tin the area with solder(62,63).
- Place the grommet in the hole on the side of the can(64).
- Next we need to install the “harmonic screw.” This screw can be tightened against the bottom of the styrofoam cup to act as a vibration node, theoretically doubling the resonant frequency of the cup. In this particular system there are several other factors involved with how well the cup vibrates so the harmonic screw's effect is not as pronounced as it could be, but it does offer a different tone when it's engaged.
Place the #6-32 nut on the 2” #6-32 screw about 3/4” down on the shaft(65). Put the screw in the center hole on the bottom of the can from the outside(66). From the inside of the can put the #6 lock washer on the screw(67). Then put the other #6-32 nut on the screw and tighten it down snug(68). On our tin can mics we found it helpful to add a little bit of thick contact cement or epoxy around the outside of the nut (on the inside of the can)(69,70). If you do this you must be very careful to keep the glue away from the screw so that it still can turn through the nut. Let the glue dry before continuing.
- It's time to attach the PCB to the can. First we need to solder on the XLR cable. Strip off about 1/2” of outer insulation from the mic cable attached to the XLR jack. When stripping the outer insulation be careful not to cut too deep and cut through the thin copper wires acting as the cable shield. Pull all of these copper shield wires to one side of the cable and twist them together(71). Pull the layer of foil and the cotton strings to the other side of the cable and cut all of them off with your snips(72,73). Strip off about 1/8” from the white and red wires(74). Tin the twisted copper shield wire, the red wire, and the white wire(75).
- Pinch all three wires together on the mic cable and put the cable into the grommet from the outside of the can(76). Pull the cable all the way through the can until the XLR jack butts up against the grommet(77).
- Solder the cable to the PCB(78,79). The red and white wires go in the square holes marked “XLR2” and “XLR3.” The red or white wire can go in either square hole. The copper shield wire goes in the round hole labeled “XLR1.”
- Solder the ground wire to the tinned part of the inside of the can(80). This can be a tricky step which may take some practice(81). We've found it helps to tin the ground wire. It also helps to bend the wire in a way to help the tinned wire to lay down flat against the tinned part of the can. Be patient and don't burn yourself with your iron. You'll get it.
- Use the other M3 screw to attach the PCB standoff to the hole in the bottom of the inside of the can(82,83,84). Make sure the side of the PCB that has the mic cable soldered to it is closest to the grommet(85). Lay the ground wire flat against the bottom of the can.
- Now we need to attach the rubber band to the inside of the can so that it will hold the cup in place. The rubber band will stretch in the shape of a hexagon, using the 6 holes you drilled in the can earlier. Stretch the rubber band over the styrofoam cup so the red piezo wires run through the band(86). Pinch the rubber band into a very tight loop and slide it through one of the 6 holes(87). Use one of the leads you cut off the resistors or capacitors earlier to hold the rubber band loop in place (note the pictures 88,89). You may want to use your pliers to bend the ends of the lead over to keep it from falling out(90). Stretch the rubber band through the hole on the opposite side of the can and use another component lead to hold it in place(91). Continue this process until the rubber band is in the shape of a hexagon and securely held in place by the component leads(92,93).
- Make sure the “harmonic screw” is mostly screwed out of the can and push the styrofoam cup into the can. It should be lightly suspended by the rubber band in the center of the can(94,95).
- Retrieve the top rim of the styrofoam cut that you cut off earlier. We will use this to hold the nylon stockings on top of the can. Most likely the rim of the cup is a little too small to fit over the top of the can, so use sandpaper to evenly remove some of the styrofoam from the inside of the rim until it fits snugly(96). We've found that anything from 60 to 150 grit works well for this, but be careful not to remove too much. Use trial and error until you have a good, snug fit.
- The nylon stocking acts as a pop filter to keep fast moving air from reaching the styrofoam cup. Put the stocking around the end of the can and stretch it tight(97). Place the styrofoam ring around the can and stocking to hold it in place(98). Trim off the excess stocking with scissors(99).
Step 5: The Ring
- Embroidery hoops usually consist of a split outer hoop with a tightening screw, and a solid inner hoop. This build uses only the inside part of a (nominal) 5" embroidery hoop. Use the template to mark 8 lines on the hoop(100,101). Extend the lines around the sides of the hoop and mark cross hairs along the center of the rim(102).
- Center punch these marks and drill them with the 9/64” bit(103,104). Make sure you drill very slowly otherwise it could blowout the back or the hoop could break. This will be safer and easier if you can back up the hoop with a baseball bat or a piece of closet pole.
- Cut one of the rubber bands to make it straight(105). We've found that cutting the rubber band at an angle helps it to thread through the holes(106). Attach a paper clip on one end of the rubber band, or clamp the rubber band end in a vice. Feed the other end of the rubber band through one of the holes you just drilled(107), from outside the hoop to the inside. Now follow the template for how the rubber band threads around the hoop(108,109). Tie the ends of the rubber band back together with a solid square knot(110,111). Trim off the end of the rubber band after you tie the knot(112). Repeat this step for the other rubber band on the hoop(113,114).
- Glue the nut on the side of the ring with epoxy or thick contact cement(115,116,117). This will allow you to use an adapter to attach it to a microphone stand. Try to keep the glue off the rubber bands. Let the glue dry before continuing.
- Once the glue is dry place your tin can microphone in the ring allowing the rubber bands hold the can(118). Adjust the can until it is suspended parallel to the sides of the ring (or put another way, until the can and the ring are coaxial).
- Use two zip-ties to attach the XLR jack to one side of the ring(119,120,121). This will act as a strain relief for the mic cable and the circuit board.
Step 6: Using Your Microphone
- The Harmonic Screw
The great thing about making your own microphone is that you get to modify it and customize the way it sounds. One of the easiest ways to alter the tone of this mic is to use the “harmonic screw.” When activated, this screw touches the center of the bottom of the styrofoam cup, creating a vibration node at that point, which allows the cup to vibrate equally around that point. Theoretically, this causes the second harmonic to be emphasized. In practice, there are already so many other harmonics embellished (by way of how the cup is held, the shape and size of the cup, and even the material of the cup itself) that the “harmonic screw” creates a subtle effect, but yet it is still recognizable. To use the “harmonic screw”, loosen the #6-32 nut away from the can. Very gently rotate the screw on the back of the can clockwise until you feel some slight resistance from it touching the bottom of the cup. Do not over tighten or else it could dislodge the cup from the rubber bands that are holding it in place -- or worse, you could poke a hole through the cup. Re-tighten the #6-32 nut tight against the can(122,123).
- Tuning the Cup
Another easy way to modify the sound of your microphone is to “tune” the cup by dampening out some harmonics by using sticky-tack. This is mostly a trial and error approach to finding what sounds good. Very carefully remove the styrofoam ring and nylon stocking (124). Gently place 2 or 3 small, pea sized, flattened balls of sticky-tack on the bottom of the inside of the cup. Place half of the sticky-tack on the piezo disc and half on the bottom of the cup (125,126,127). Adding mass to the cup like this alters the resonant frequency and tones down the higher, harsher harmonics and smooths out the midrange.
- More Experiments
There are many more options for modifying your microphone that you could play around with. One thing that would be fun to explore would be how the polar pick-up pattern would change with different amounts of holes in various parts of the can. Another idea that would be interesting to try out would be to hear how different types of cups resonate in different ways...such as paper or plastic, compared to styrofoam. Another modification that could be explored would be how can sizes change the tonality of the mic. The possibilities are endless. Be creative and keep exploring until you discover a sound that is so unique that it just has to go on your next album!