The Furball XY Mic

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Introduction: The Furball XY Mic

About: I started taking things apart when I was 6 started putting them back together at 8 and they actually worked again when I was 10 or 11...

This instructable will show you how to build an XY stereo microphone. One intended to be used on a DSLR or mirrorless camera. It is built into a wiffle ball and covered with fur. This provides a built in “Dead Cat” for wind protection. The heart of this mic is a pair of fantastic microphone capsules, the TSB2590’s. These are very similar to my favorite TSB2555B, except they have a built in Field Effect Transistor or FET, which makes interfacing very simple. Literally all we need is some wire and a connector.

Supplies

Step 1: The Capsule: TSB2590

The TSB2555B has excellent audio specifications. I was thrilled when I discovered this capsule and promptly ordered a few to experiment with. Traditionally the top DIY mic capsules are from a company called Primo, headquartered in Japan. Primo is an OEM supplier to Sony and many other well known name brands. They don't sell directly to DIY people and are a bit secretive, but there are a few websites where you can order them. This one for example: https://micbooster.com/18-diy-maker

Unfortunately for me, that site is in Europe and shipping is expensive. Transsound makes the TSB line. They have been around several decades and are also a large OEM supplier for multiple companies, including several big microphone vendors. They pioneered large diaphragm electret capsules. The TSB 2590 is available from JLI electronics for $12.95. (See parts list) It is quite amazing, and at 25mm it has the classic few db bump in the 10-15Khz range, adding a bit of presence. It also has a very quiet internal FET, giving us a studio grade S/N ratio of ≥ 70db.

Step 2: Capsule Wiring

The TSB2590 is a “three wire” vs “two wire” capsule. What that means is that the microphone capsule brings out both the Source and the Drain connections of the internal FET. The benefit of this is we have more options for wiring the FET to external circuitry. On the back of the capsule we have “S”, “D”, and “G”. “S” and “D” are the source and drain connections. The “G” is actually ground, not the gate connection. Because of their construction, all FET’s have an intrinsic internal diode. Normally it is designed to cause minimal issues. For use in an electret microphone, it is designed to provide a small amount of leakage current. That leakage current can substitute for the external 1GigΩ resistor, normally used in the FET biassing circuitry of microphone electronics. This simplifies things even further. Because of this, the gate connection is connected directly to the capsule internally and there is no need to bring it out externally.

Having both the Source and Drain lets you choose one of three interfacing techniques for FET amplifiers. Those are: Common Source, Common Drain, or a hybrid, where both are used to obtain a phase splitter. We are going to turn the capsule back into a two wire configuration by connecting the source to ground, then taking the signal out from the drain connection. This is how most electret capsules are wired, making it even easier for us! However, there are benefits to the other two, and in future instructables, we will be using some of those as we put this fantastic capsule to other uses.

Step 3: What Is an XY Mic Anyway?

So what is an XY microphone anyway? It is based on a recording technique that uses two cardioid microphones with the capsules mounted 90° apart from each other. It provides a nice clean stereo image that easily collapses into mono if you need to. It also does not require spaced microphones, which on a camera, would be challenging. Read more about it here: https://en.wikipedia.org/wiki/Microphone_practice...

Step 4: Build It

I built a kludge prototype with some foam rubber and a ½” ring of 2” PVC pipe to verify the concept. The design lent itself to being suspended in a sphere, but where would I find a simple inexpensive one with holes in it? That is when I thought of a wiffle ball. So I ordered a few of those. While I was waiting for my Amazon delivery, I reached out to a friend of mine, Tom Benedict from the MicBuilders forum. I told him about this capsule and what I wanted to do with it, that I wanted to use two capsules in an XY configuration suspended via something to dampen handling noise etc. He immediately suggested using hair bands as they are robust, readily available and kind of self dampened due to the thread wrapping on them. He offered to design a capsule holder that could be 3D printed and used those hair bands. Less than an hour later, he had it loaded up on shapeways and sent me the link. I ordered several immediately!

When it all arrived, I built one. See the build video above for assembly instructions

Step 5: Final Results and Use

I am very happy with how this came out. The capsules wired this way are pretty sensitive and for my Sony A7iii, I set the audio gain to “8” out of 30. This isn’t the mic to use on a kick drum, but it is great for capturing ambience and the sound field in front of the camera. It is way better than the internal microphones, which isn’t really a high bar to begin with. I wasn’t sure if the wiffle ball would color the sound or have internal resonances but it does not. The mic is also a bit more sensitive to handling noise than I expected, but filtering 80hz and below in post really makes a difference. Also, the fur I am using may not be the best choice. I did have a bit of wind noise and I am looking into better fur. I will update this if I find some. It also makes a great nature recording mic when used on any 3.5mm input recorder such as the Sony PCM-A10, Zoom h1n or equivalent.

To read more on FET circuits see these two articles. The common source, which is what we are using has voltage gain, which makes the mic more sensitive at the detriment of lower SPL handling ability. The common drain has unity voltage gain which makes its use less sensitive with a higher SPL handling capability. For an on camera microphone, we really want the sensitivity vs max SPL.

https://en.wikipedia.org/wiki/Common_source

https://en.wikipedia.org/wiki/Common_drain

I am super impressed with this Capsule and already have a list of projects for it, several of which will be for video use. All will be featured in upcoming Instructables. If there is a mic type, you would like to see, mention it in a comment and I will see what I can come up with!

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    7 Comments

    0
    maz12
    maz12

    10 months ago

    Very interesting design. One major question on the XY arrangement of the capsules in this design. Why didn't you offset the capsules vertically so that the capsule's centers are aligned (i.e. the typical XY arrangement pattern that you see in the Zoom h1n recorder, for example).

    0
    DJJules
    DJJules

    Reply 10 months ago

    i did this more on mounting considerations. And, back in the day with a pair of cardioid AKG pencil mics, we aligned them like this.

    Jules

    0
    maz12
    maz12

    Reply 10 months ago

    Presumably this would result in better imaging by aligning them vertically.

    0
    maz12
    maz12

    10 months ago

    In terms of other capsules instead of the one in this design which looks unavailable, would the CMC-9745-37T3 be a suitable replacement candidate? 72db SNR and -37db sensitivity.

    0
    maz12
    maz12

    Reply 10 months ago

    Oh yes I see the link now, unfortunately the Jli electronics one doesn't have a datasheet. The linked CMC model is a unidirectional mic, which I presume is a cardiod mic capsule. Is there any particular reason you suspect it wouldn't work?

    0
    DJJules
    DJJules

    Reply 10 months ago

    Uni is Cardioid so yea! I mess read it