Things are still going quite well for me at the cathedral. Last week I had the chance to help out with a grade 8 retreat, which involved presiding at a liturgy of the word. I was also at the Centennial Auditorium (TCU Place) to help out with the BJM High School graduation Mass, and was invited to the banquet afterward. It was huge, compared to what I’m used to: ~350 graduates; 1500+ for the banquet.
So.. Microphone’d!! v2.0. I checked out some of the past discussions on the micbuilders group on Yahoo and saw that several people had built electret condenser mics that used a larger, higher quality capsule than the Panasonic capsules that I had used before. It uses a Transsound TSB-165A capsule.
I based the circuit on a microphone that was built by someone on the micbuilders forum, though with a slightly different (possibly lower quality) JFET at the capsule. I bought some 1″ aluminum tubing and cannibalized a cheap, $2 karaoke mic for the bulb on top. The finished product definitely looks home made, but it’s probably good enough that if I needed to have it in the chapel, it wouldn’t stand out too much. I still need to epoxy the screw-base of the bulb and the filler plastic I used around the connector at the bottom. Otherwise, though, it seems fairly solid. A 60Hz hum was pretty noticeable until I shielded the mic capsule with a combination of aluminum foil (only in certain spots) and wire mesh from a strainer.
The finished product is very sensitive and sounds pretty good. I’ve noticed that my room is fairly noisy: it’s right next to a well-travelled city street and there is a music festival going on at a nearby hotel, so I have a steady drone of bass sounds coming in. What’s amazing is that if I wear my headphones (decent external sound-blocking), put the mixer’s input gain to the 1/2 mark (so, I’m guessing, 30dB), and set the channel level to 0dB (unity), the microphone is sensitive enough that it picks up a lot of the street noise outside. This sound level is easily loud enough so that I merely have to whisper into the mic to have it pick me up well.
The capsule is supposed to have a cardoid pick-up pattern, and it seems to follow it reasonably well. Sounds from behind the mic are much quieter than from in front of the mic, although my room echoes a lot and so I can’t really test this well. I don’t have any equipment for measuring the frequency response. The higher end seems to have a bit more emphasis than the low end, though it’s hard to tell. That would certainly be consistent with the capsule’s data sheet, anyway.
OK. Enough text. Time for photos! Soon I hope to have some recordings up as well.
Until next time, keep your stick on the ice!
1. The Transsound TSB-165A capsule, with the extra 1-gigaohm (!!!) resistor and JFET. The resistor has been encased with plastic cement to avoid moisture changing the impedance.
2. The circuit, all wired together. The wires to the connector were shortened somewhat in the final version.
3. A close-up of the main circuit board. Getting electrolytic capacitors (the larger cylinder-shaped components) to not take up so much room was a bit of a challenge.
4. The aluminum tube (approx. 6 inches long) and other items that went into the microphone (more or less – the MacBook is not part of the mic!).
5. The finished product!