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Condenser mics (WM61A) with Phantom powering

Description
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.

Linkwitz mod
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:

 

© Siegfried Linkwitz

 

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.

Phantom
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:

© Richard Mudhar

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!

Sources
Siegfried Linkwitz - http://www.linkwitzlab.com/sys_test.htm
Richard Mudhar - http://www.suite101.com/content/how-to-use-an-electret-capsule-with-p48-power-a150317

Comments (4) Trackbacks (1)
  1. can you give me some wav samples

  2. Hey, I’ll try to put out some samples when we start recording with the mikes.

    /XeNo

  3. I’m a electronics beginner but can follow the schematic pretty well. I still have some questions.

    1) I know that the WM-61a just have a decent selfnoise and that there are quieter capsules out there, but from what I’ve seen they lack in frequency response compared to the wm-61a’s. I’ve got 2 pair of binaural mics with these capsules, both are unmodified and use plug-in power of a zoom H1. I’m looking to make the wm-61a’s least noisy as possible. Powering them with P48 will let me record higher SPL, but will they also record hotter? So I will achieve the same levels with lower gain and thus reduce the noise?

    2) I’m sorting out the parts for this build, but I’m not sure which pats to get for the capacitors. I find it a bit confusing as they come in different voltages, they are radiale or axiale, MKS2, MKT, SMF etc. Which would be the best for this build?

    • 1) I don’t know for sure, but using the Linkwitz mod should be the way to go. Just powering them with P48 won’t make the capsules record higher SPL as far as I know.

      2) I’ve used >=16V electrolytic caps. Some radial and some axial, whatever is more practical when it comes to building the circuit.


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