The Sound Sleuthers

The Sound Sleuther is a top notch microphone based on the PUI 5024 mic capsule. They are really quiet and sensitive, making a perfect nature microphone. They are inexpensive as well at under $3 each in quantity of 10. They have an internal FET which makes interfacing to them very easy. This instructable will show you how to make a couple variations allowing you to capture some pristine audio. Because of the mic’s sensitivity and noise floor, it is optimized for quieter sounds. It is not for use on a drum kit. It is perfect for ambient, nature, speaking voice, and ASMR sounds. It is inexpensive and easy to build. You will want several in your audio arsenal. They are cheap enough that you won’t mind placing them in harm's way in search of that elusive sound. We are going to build two versions, one PIP or “Plug in Power” and a P48 version for professional recorders and mixers that use 48 volt phantom power. Both offer stellar performance regardless of the powering method. For the PIP version both a mono and stereo version.

Background

A condenser microphone is in essence a capacitor, which is nothing more than two conductive plates separated by a small distance. If we make one of the plates out of flexible material that can vibrate with sound, it will convert those vibrations into an electrical signal that we can record. Top end studio condenser microphones require an external charge to produce a signal. An electret condenser microphone has a permanent charge built in. The PUI 5024, like most small electret capsules, has an internal Field Effect Transistor (FET) built in, making the rest of the electronics even simpler. Check out the circuit below.

The black dashed box contains everything inside the capsule. The blue dashed box represents the rest of the circuit. And, it is already built into any recorder, camera, etc that supports Plug in Power or PIP. All we need to do is connect the two boxes with some wire.

The wire needs to be shielded to minimise any electrical noise from entering the system and degrading our sound. We are going to use Mogami W2697, two conductor shielded. It is pretty inexpensive but most importantly, easy to work with. I have tried others from both Mogami and other vendors, this one is the simplest to strip and solder.

Parts List:

The Capsule: https://www.mouser.com/ProductDetail/665-AOM-5024L-HD-R

The wire we are using (And yes, you want to use this…) https://www.redco.com/Mogami-W2697.html

UPDATED: The 1/8" Connector https://www.redco.com/Rean-Neutrik-NYS231BG.html

Male XLR https://www.redco.com/Neutrik-NC3MX-B.html

68K ¼ W https://www.mouser.com/ProductDetail/Yageo/MFR-25...

3.3uF capacitor https://www.mouser.com/ProductDetail/Panasonic/EE...

Electrical Tape: https://www.amazon.com/AmazonCommercial-Electrica...

E6000 Glue: https://www.amazon.com/E6000-230012-Craft-Adhesive...

Tools needed:

Small wire cutters, Needle nose pliers, Soldering iron, Electronic solder, Single edge razor blade

Small vice https://www.amazon.com/PanaVise-381-Vacuum-Base/d...

Alligator clip third hand rig https://www.amazon.com/PanaVise-381-Vacuum-Base/d...

Single edge razor blades https://www.amazon.com/PanaVise-381-Vacuum-Base/d...

Wire strippers (that go to 26 gauge) https://www.amazon.com/PanaVise-381-Vacuum-Base/d...

“Bonus Lap” items:
Mini “dead cat” windscreen: https://www.amazon.com/gp/product/B076Z5TGXH/

Brass tubing just bigger than the mic cable: https://www.amazon.com/gp/product/B002C0SPSU/

Foam windscreen: https://www.amazon.com/gp/product/B002C0SPSU/

Foam cable sleeve: https://www.amazon.com/gp/product/B002C0SPSU/

The first set of these is what I call the PIP build for use with devices that have an ⅛ inch jack. This includes cameras, miniature recorders, anything with an1/8th inch jack (or 3.25mm even if the math isn't exact…) We will build a mono, or single channel mic and a stereo pair connecting two capsules to one jack. Before building here is something to think about and the cool part of this project. You can make the wire as long or as short as you need. So build several of different lengths. I have a mono one that is a foot long, perfect for attaching to my Sony A7iii. Then I have a couple of the P48 versions that are 25 feet long, for use as ambient sound and outriggers for a Decca Tree. More on those in future instructables!

First step is prepping the wire to solder to the capsule. I use a single edge razor blade to remove about ⅜ of an inch or so of the outer jacket. Then peel back the inner copper shield layer. What I like about the wire we are using is that it is wrapped, not braided. Which is much easier to work with. Cut away the shielding layer flush with the jacket to expose the white and red inner wires. We are using the shield as it will be connected to ground at the connector end. Now strip back just a little bit the insulation from the red and white wire. You only need a little as the insulation will stretch and snap back. Tin each of the wires and then solder the red to the “+” terminal and the white to the common (Ground) connection. We will seal this and strengthen the joint with some E6000 adhesive after we test them.

Now we prep and solder the connection to the ⅛” plug.

Caution: Ensure you have the housing and the plastic sleeve insulator on the wire before you solder it to the plug. I can not tell you how many times I have forgotten this… Here are the steps:

1. Place the metal housing with spring on the wire facing the correct direction
2. Place the plastic insulating sleeve on the wire
3. Prep the wire, strip etc.
4. Double check…
5. Now Solder

Prep the wire by stripping back the jacket about ¾ of an inch. A bit extra is the key here we will trim the excess as we connect the red wire. Separate the shield exposing the white and red wire. Now for the shielding magic, strip the white wire as close to the shield as possible. We are going to connect them together and then solder to the ground or common connection on the jack. This provides shielding and minimizes RF and EMI noise. Twisting the stripped white wire and the shield together and then tin them with solder. Cut back all but about an ⅛ of an inch.

With the plug body held snuggly, tin the inner top portion of the ground connection. Now, solder the shield portion of our Mic cable to the plug. Careful not to burn a finger here. Hold still while the solder solidifies. Now we are going to push the ring and tip connections together. We will connect the signal wire (the red one) to both of these. This lets us use the mic on mono connections. Trim the red wire so that we can strip back enough insulation to solder to the common tip/ring connections. Eyeball the wire and strip back enough insulation to make a connection without excess slack or stretching the wire to make it reach. Tin the wire and then feed it through both of the tip/ring connection points. If this is too difficult, tin the pushed together connections and solder the red wire to them. Either will work. Trim any excess sticking out. Let the plug cool and inspect it for anything awry. Slide the plastic sleeve over the connector and then screw on the housing.

Before the final step, plug the mic into your device of choice and test it. Once you know it works we are going to suspend the mic in one of the alligator clips from our third hand rig and coat the top with E6000 glue. Don’t worry about how it looks now as it shrinks as it dries.

If you are wondering why we used a stereo jack for the mono version, it is to allow it to work with mono cameras like the DJI Osmo Pocket and Osmo Action, along with the Rode Wireless go and similar devices. And to work with stereo devices like Sony Cameras and GoPro’s. The signal will be mono but recorded to both left and right channels on those devices.

The stereo version uses two capsules and one jack. One wired to the Ring and one to the Tip connection. The capsule connection and soldering part is identical. I would build the first set with about 6 feet of wire. This will cover most situations. I have a pair that is three feet and one that is ten. I use the 6 ft one most often. The ten footer lets you use these as lavaliers on two people for an interview. Prepare the capsule wiring just as before. For the plug connection discard the spring portion of the jack housing and slide that over both wires followered by the plastic inner sleeve. This is worth repeating:

1. Place the metal housing without the spring on the wire facing the correct direction
2. Place the plastic insulating sleeve on the wire
3. Prep the wire, strip etc.
4. Double check…
5. Now Solder

The big difference on the soldering part is we need to combine all the shield wire and grounds. For each wire strip back about ¾ inch of the outer jacket. Then strip the white wire flush with the outer jacket. Now twist all of these together in one bundle and pull to one side. Now tin this with solder. Cut all but an ⅛ inch or so. With the jack body in the vice facing you, tin the top portion of the ground/common connection. Now solder the combined shield and ground to this. Let it cool and tug gently to make sure the connection is solid. Now we will cut each red wire to the correct length, eyeballing it so we can strip it and connect it to the appropriate tip or ring connection. Unlike the mono version, we are going to tin the red wires then solder to the outside of ring and tip connections. See the photos for a better explanation. After they cool, slide the plastic sleeve over the jack and then screw down the outer sleeve. Test the mics to ensure they work then apply the E6000 glue to seal the mic connection just like the mono version.

This version uses 48V Phantom power and XLR connectors. It uses a highly regarded but very simple circuit called "The Simple P48". To quote many of us that build mics: "I didn't come up with this circuit but I wish I had" It was conceived by David McGriffy. It consists of two additional components, a 68K resistor and 3.3uF capacitor. These combined with the input circuitry of the mic preamp to properly bias the internal FET of the PUI-5024 capsule. The 68K is optimal and selected specific to this capsule. If you are using a different capsule please refer to the Simple P48 document. Other capsules will need a different resistor value. The capacitor can be 1uF to 4.7uF without noticeable change in sound. I am using 3.3uF. You want an aluminum electrolytic. You can use one rated for 10V but I am using one rated for 63V both because I already had them and with the max voltage of 48 available, worst case scenario -- incorrect wiring etc. it is rated above that. The real requirement is that it and the 68K fit inside the XLR jack. With the wiring we are using, this is pretty easy. There is also one other difference, and it is important! The capsule case, which would normally be at ground potential, is NOT in the P48. It is above that and must be insulated. This can be either a wrap of electrical tape, putting the capsule in a windscreen or mini furry dead cat. Other people have used heat shrink tubing, as have I in the past. If you do, be careful of the heat on the capsule. Use a heat gun not a lighter or open flame. The included "Simple P48 Doc" written by Richard Lee is from the Micbuilders forum https://groups.io/g/MicBuilders/topics. If you are really into this project and want to learn a lot more send an email to MicBuilders@groups.io and ask to join. I am one of the moderators there.

The capsule wiring is identical. We use the shielding as before. Cutting it at the capsule end. Note: It is no longer connected to the white wire and in this case truly is shielding all the wiring. Some builders of this use extra copper foil or screen to extend it around the capsule. You will need a layer of insulation between the capsule and this if you choose to do this. I have not had an issue with EMI or RF in my builds. The difference is all in the XLR connector. Check out the circuit below. It is originally by David McGriffy and the graphics are by Lucas Falkenhain. I Deviate from it as I don't connect Pin one to the connector ground. I have not had any issues. First step is to slide the XLR outer sleeve over the mic cable. The inner plastic piece is actually split and can be put on later but I am in the habit of always sliding this one as well. Bend the negative (-) lead of the capacitor and bend it up and along the body of the capacitor. Take the 68K resistor and hold it flush with the bottom of the capacitor, next to the (-) lead. Twist the resistor lead and the (-) capacitor lead together. Using the “Third Hand” alligator clip thing to hold both together. Solder the resistor and capacitor leads together. Now trim them back leaving enough to connect the white wire to later. Clamp the XLR connector piece on a small vice or other means of holding it. Ensure you identify Pin 1,2,3 correctly! Tin all three pins with solder. Now take the resistor capacitor assembly and trim the two leads to allow easy connection to Pin 1 and 2. Tin the leads. Then solder the resistor lead to Pin 1 and the capacitor lead (+) to Pin 2. Now it is time to prep the microphone cable and attach. Double check the connector parts are already on the wire! Trim back about an inch of the outer jack and twist back the copper shield. Trim this and then cut it to about a ¼ inch. See the photos. Trim the Red wire to about ½ inch over all and strip about ¼ inch and tin. Solder the shield wire to Pin 1 and the red wire to Pin 3. Now line up the white wire it can be trimmed, stripped and soldered to the junction of the resistor and capacitor. Inspect everything to make sure the connections are good and that there are no shorts. We are going to take a small piece of electrical tape and wrap it around the connector parts to ensure no shorts when the connector housing is screwed on. Start between the capacitor body and the resistor/cap leads. Wrap around until the whole assembly is covered. Now slide the connector into the XLR housing. Carefully push in the plastic insert aligning the internal slot with the outer tab. Screw on the shell and we are finished!

These fit well into the Movo MCW8 of Lavalier Microphone Windscreen Muffs. They are made for a 12MM Lav and these are about 10MM and fit in just fine. I tried a couple other ones and they either fit too loose, with the mic flopping around inside or were impossible to get the capsule into.

One other thing I tried that works really well is to put a short piece of 5/32 inch brass tubing over the wire either glueing it near the capsule using a small foam piece glued to the capsule with the E6000 glue.

The capsule sensitivity is -24db (+/-) which is 10-20 db higher than a lot of other electret condenser capsules. This means they don't need as much gain as other microphones. Combine that with an 80db signal to noise ratio and they are perfect for quieter sounds. We can put them very close to things that we wouldn't put other microphones near. So let's listen to them in action!

Final thoughts:

These are the perfect capsules for the starting point of other recording projects. They could go into a PZM design or an exponential horn. What can you do with them? I hope you enjoyed this instructable. I will be featuring these mics on my youtube channel Sound Sleuth so if you enjoy strange and different sounds, please subscribe to that. I also will post the audio with no compression on SoundCloud.