I recently bought some Panasonic WM61A condenser electret capsules from eBay ($10 or so!) and thought I’d give them a go. From what I had heard the frequency response curve was supposedly very flat, making them ideal as measurement mikes.
After building one mic using a copper pipe and running it through a powering circuit I’d built on my breadboard, I found that it was really sensitive and was not suitable at all recording high SPL sources. Then I came across Siegfried Linkwitz’ mod for the WM60AY. The principle is to cut a small copper tracing in two and soldering a wire from one of the terminals to the housing, disabling the internal FET amplifier stage. After doing so and building an identical mic as the previous one, the difference was remarkable. The frequency curve was more distinct and could withstand more of an audial beating. This image from Linkwitz’ page shows a normal and modified capsule:
And here are the (ugly) mics I put together. One with the original WM61A capsule, and one with the Linkwitz mod. The mics housings are made with ordinary copper pipes, with silicone in both ends to attach the microphone elements and the leads. Simple and ugly. But it works.
The circuit I had been using to power the WM61A’s had involved a 9V battery, which would be impractical while recording. I did not want to have another potential source of error, having to check the status of a 9V battery in a mic… so I found an article by Richard Mudhar that described how to build a Phantom (+48V) powered circuit for the capsules. It also inverts the signal on one of the pins, making it a balanced signal suitable for long stretches of XLR-cables. Here’s the schematics for the circuit:
And here are some pictures of the circuit in a neat hobby enclosure. It turned out pretty ok.
I mounted a female mini-jack connector to the enclosure. Combined with the male mini-jack plugs on the mics, I can easily switch between the microphones.
When it comes to placing the mics in a microphone stand, the leads to the microphones are a too short. Also the weight of the Phantom/XLR-box makes the mounting impractical.
So I made 2 meter mini-jack extension cable to circumvent this problem (not in picture).
I’m currently recording an album with my band, so I can’t wait to test these babies out!
Siegfried Linkwitz – https://www.linkwitzlab.com/sys_test.htm
Richard Mudhar – https://www.suite101.com/content/how-to-use-an-electret-capsule-with-p48-power-a150317