Many units like the Edirol R-09 etc have 'plugin power'. NOTE: These capsules require plugin-power (a low voltage phantom standard) to work, that is 2V (min) - 10V (max) down the mic cable to work. Buy some Panasonic WM-61A capsules ( on eBay ~$15 for 10). They offer several different circuits, this particular one is titled вЂњBest So FarвЂќ at the bottom of the page.Step 1. The one I decided to go with comes from good guys at Direct Approach website and itвЂ™s based upon BehringerвЂ™s ECM8000 mic. ThereвЂ™s a bunch of different circuits and most involve either a pair of transistor or an op-amp.

ThatвЂ™s it! If you did everything right, your capsule should look something like the capsule from the photo on the left. ItвЂ™s sufficient to go halfway through and thin aluminum will give in once you try to peel it off the trace. Just make sure that you donвЂ™t cut too deep and damage the trace. Now repeat the same for the second cut and you should be able to lift the casing lip, exposing the trace. The way I did it was to place the blade against the casing and lightly tap the knife with the palm of my hand until it cut into the lip of the casing. To do that, we need to cut through the aluminum casing and peel it off. We can uncover part of the casing and expose some copper trace that we can use to solder the ground lead. We canвЂ™t solder to the casing, but there is a copper trace on the PCB itself that goes around the edge of the board and is normally covered by the lip of the casing. As you can see on the photo above, there is a tiny circular PCB that is encased in the casing. Now onto the next step вЂ“ making it possible to solder to the casing. After cutting, make sure thereвЂ™s no continuity between the casing and the solder pad. Try to remove as much of the trace as possible to prevent it from bridging back together once you start to solder the leads. Cutting the trace is the easier part of the job. On the photo above you can see a modded capsule next to the stock capsules. YouвЂ™ll need a sharp blade, xacto knife or something similar. Make sure you get more than one capsule, as itвЂ™s easy to screw up and destroy a capsule in the process. The second problem is that the casing is made of aluminum and itвЂ™s difficult, almost impossible to solder to. They are hard handle, hard to cut, hard to solder and easy to lose. It may look big on photos, but in reality 6mm is very small. The first problem is that the capsule itself is tiny. In theory, this sounds pretty easy, right? Well, itвЂ™s not that easy рџ™‚. Then we can solder two leads to the terminals and the third lead to the capsule casing. That involves some precision surgery on the capsule and cutting a thin copper trace that connects one of the two terminals with the capsule casing. According to Linkwitz, much better performance can be obtained from this capsule if we break this connection, wire the capsule with three leads and bias the FET ourselves. In other words, the FET will operate in common source mode. WM-61A capsules have an integrated FET that has its source terminal hard-wired to the capsule casing, which means that it will be grounded when wired with two leads as intended. WM-61A based microphone can be built for less than $20, so it was a great introductory project into the world of mics for me. You can still find some on the eBay (together with a bunch of Chinese clones advertised as the real thing), but there are also good alternatives, such as Primo capsules. Unfortunately, like with some other components that are loved by the DIY community (J201 FETS come to mind), they are discontinued by Panasonic. WM-61A capsules are praised for their super flat response and good signal-to-noise ratio. Projects built around Panasonic WM-61A electret ( datasheet) capsules are on the top of the results when you search for cheap but decent mics.

I needed a simple (and cheap) microphone with flat frequency response and decent noise level to record acoustic guitar.

Panasonic wm-61a capsules