Now that your iPhone can capture 4K video and most DSLR's can record 1080P usable for filmmaking, the one thing that separates great video from mediocre video is the audio. Most of the time having a simple lavalier or lapel microphone can make all the difference between something usable and something totally “cheap” sounding. Most camcorders, phones and DSLR's have external microphone jacks which are used far less than they should! You can purchase aftermarket microphones for this but how much fun is that? All we need to do is wire up a microphone element to the correct jack and voila! Instant external microphone perfect for a lavalier or other use. In fact, we can actually build very good ones inexpensively. This instructable will show you how to make external microphones for use with most of these devices. iPhone and Android devices have one microphone input and thus are mono, while most DSLR's Camcorders and portable recorders such as the Zoom H4n are stereo. We will build mic's for both of these. Check out a short demo video
Step 1: Finding Parts
After my mod a cheap Chinese mic instructable I went back the roots of my first experiments with microphone capsules. Specifically the Panasonic WM-61A mic capsule. This was a great little capsule that was widely used in the DIY community. The difference between it and the capsule I used in the other instructable is that the Panasonic capsule has the FET built into it already much simplifying the circuitry required for use. Unfortunately it is also obsolete. I had four left from a Digikey purchase a few years ago but needed a replacement if I were to use it in a project. Looking through JLI's website here I found the JLI-61A which suspiciously had the same specs as the Panasonic WM-61A. Time to order ten of them and see how they compared. I was pleased when they showed up. Physically they are identical and they are on par sound wise if not a bit quieter.
How they work:
These are electret capsules similar to the ones I used in my previous instructable with one big difference. They have an internal FET transistor to interface to the outside world. The FET has an additional feature of an internal diode that has enough leakage current that it can replace the 1gig ohm resistor that is used in the “Alice” or Schoeps circuit used in the other instructable. See figure-1 Box “A” contains the capsule and the FET all in one nice small package. Box “B” contains the rest of the electronics needed to pull of the microphone signal and send it to what ever is next. The cool part of that is most devices that can use a microphone capsule like this already contain the capacitor, resistor and supply the 5 volts DC. Most of the FET's can be supplied from 1.5 to around 10 volts DC and will still work. Supplying power like this is called “Plug In Power” or PIP microphone power. Things that supply this include PC sound cards, Mac laptops, smart phones, dedicated recorders and DSLR cameras with microphone jacks. All we have to do is wire the capsule to a 3.5 MM jack correctly and we have an quick and easy external microphone.
Lets Build a few!
There are three basic styles of this:
Mono input to a smart phone using a TRRS 3.5 MM jack (iPhone and Android)
Mono input to a PC sound card
Stereo input to an external recorder such as a Zoom H4N or a DSLR
Here is what we will need:
The microphone capsules. Available from JLI electronics here.
Thin single conductor shielded wire. I used Mogami wire. Specifically the W2330 for single conductor and W3031 for two conductor. We don't use the two conductor in this instructable but it is great wire.
There are multiple sources for stereo 3.5MM plugs and I already had a few of those but these will work great.
The TRRS ones are harder to come by. I found some for $7 each and just couldn't justify it... So I looked elsewhere... And found these from dealextreme here. Hey! 20 of them for $7 now that I can do. Amazon also has them search “trrs plug” and you will get multiple results of varying pricing.
Heat shrink tubing
For tools you will need a soldering iron, typical electronics tools and a razor blade. Also an alligator clip “holding” jig is great for soldering to the capsules.
Step 2: Let's Build
The first thing to think about is how long of a wire do we need? There are two use cases that I came up with for this.
Case One: You can put the recorder on the person. In this case we only need about 6 feet. This works because it is pretty easy to resync up audio in most video editing programs these days. And by recorder I mean not just a dedicated mini audio recorder but an iPhone or iPod.
Case Two: You are plugging the microphone into the actual video camera. Which still could be an iPhone or iPod. In this case we may need a longer wire, ten feet or more. This circuit will easily work with 40-50 feet of wire.
First step it to strip the wire. We will need to expose the outer shield to connect to ground and the then the inner conductor. I am using spiral shielded wire. This is very easy to work with. I like to use a razor blade to strip this type of wire as it doesn't stretch the insulation and makes a nice clean edge. You have to be careful not to cut the inner wire and only the insulation. See the pictures for step by step:
- Strip about 3/8” of the outer insulation
- Peel back the spiral shield and angle it to one side
- Twist the spiral shield tightly
- Strip a vary short 1/16th of an inch or so from the center conductor
- Tin the center conductor then tin just the end of the shield. This is important so that we can easily flex the rest of it after soldering to the capsule.
Step 3: The Capsule
Second step is to solder the capsule.
Look at the capsule closely and you will see that one of the solder pads has a small conductor that goes to the edge of the capsule, making electrical contact with the shell. This is the ground terminal. See the photo with the arrow pointing to ground. The other connection is the FET terminal that we will call “Mic”. Form the leads so that they are close to each other and line up to the solder tabs on the capsule. If needed, trim the shield wire so that it is parallel to the center conductor. Carefully solder the wires to the capsule so that the capsule remains aligned straight with the wire.
Third step is to cover the capsule with a bit of heat shrink. Cut a 3/4” inch or so piece of heat shrink tubing and place over the capsule. The goal is not to cover the end of the capsule. Also, we want to minimize the amount of heat used so as to not damage the capsule. Use a hot air gun and carefully shrink the tubing around the capsule while striving to not overlap the end.
Step 4: Solder the Connector (iPhone Style)
See the chart showing the two possible connections. We are going to build the iPhone version. Which incidentally, works for for iPod touches, iPads, and macbooks.
I used a DMM to determine which lead corresponded to the correct sleeve connection on the plug. To make things easier, I cut off the other solder tabs.
Saftey Tip: Before soldering the connector on PUT THE OUTER PART OF THE CONNECTOR on the wire so that you can screw it on after soldering the wire on. Oh yea, face it the right way so you can screw it on post soldering. It is a total bummer to do a really great neat and tidy solder job on the connector and realize you forgot this step! I have done this many many times...
Start by stripping back about the same amount of outer insulation as for the capsule. Twist the sheild together as before and pull to one side. Strip an 1/8” or so from the center conductor. Tin the center conductor but do not tin the shield. See the pictures. Solder the center conductor to the normally grounded connection on the TRRS connector. Once connected, move the wire shield connection close the solder tab that it will be soldered to. Trim the shield so that it rests up against the solder tab. Tin and solder the shield wire to the tab. Bend the wire up so it exists the connector properly and slide the screw on cover down over the connector. Tighten the connector and you are done! Give it a quick test by plugging it into your iPhone and either shoot a short video or use the recorder app and record a short bit of audio. To see if it works, you will have to unplug the mic to enable the internal speaker. Do this and you should have some nice clean audio. If it doesn't work, check for shorts or a broken solder joint.
Step 5: Build a Stereo Version
This version uses two microphone capsules and a regular 3.5MM stereo jack. To build one of these we will use two pieces of wire and once again pick a length that will allow you to connect the mic and recording device the way you will use them i.e. shorter if you are putting the recorder on the person using the mic or longer if you are plugging into a DSLR or other video camera.
Step one: Prepare two identical lengths of wire and solder the capsules to them just as we did for the iPhone version.
Step two: Fed both of the wires through the plug housing (ensure it is facing the right way to screw on after soldering.) Strip back about half and inch or so the outer insulation. Twist the shield together like before and angle out from the center conductors. Strip about 1/8” from the center conductors and tin them. My particular 3.5MM plug has weird solder connections on it and yours may vary. Solder the center conductors to the tip and sleeve terminals. Carefully dress in the two wires to the connector. Solder the shield wire to the ground connection on the plug. Screw on the cover being careful not to stretch or break the inner wires. I removed the external spring/strain relief from mine due to the small inner diameter. After assembly test it with an external recorder.
Step 6: Using the Microphones
These make great lapel mic's. All you
need is a bobby pin or small hair clip to clip it to a shirt. The Mogami wire is pretty flexible and thin while being strong too. This turns an iPhone into a perfect portable interview camera and dramatically improves video made with an iPhone. You can also use an iPhone or iPod as a stand alone audio recorder while using a “real” video camera.
The stereo version works with most small digital recorders with 3.5MM jacks that supply PIP power (Plug in Power) It also works with my canon 7D DSLR however, due to the Automatic Gain Control built into the camera the resulting audio is not the best. With a suitable adaptor, they will work with a GoPro 3 or 4. (Go to Amazon or ebay and put in GoPro mic adaptor.) You can also use the stereo version to put a lapel mic on two people and separate left/right in post production.
Because these mics are so cheap to make you can use them to get close to things you might not want to use a studio microphone for.
What will you use yours for? Let me know in the comments.