Using advice that people provided on the Yahoo Nature Recordists group, I built an attenuator “cable” to connect a single microphone to an MD recorder in such a way that one channel is attenuated (11 dB) relative to the other.
My MD recorder (a Sony MZ-RH10) has only one volume control for the two channels and records in stereo even if there is only a mono input. This arrangement uses the “extra” track to provide protection from clipping by recording a copy of the signal are reduced levels.
I packaged the whole thing in a small plastic box since I often have problems with handling noise from the microphone connections when the line flaps in the breeze as it runs from the microphone to the input on the MD. The XLR connector on the box is a sturdier arrangement and the whole box scheme, which reduces the chance of jiggling the mic connection while in the field, would be worth it even without the attenuation deal.
There's room in the box for the “AA” battery case that attaches to the MD and/or a battery made from two “D” cells in the fashion described here. There's also enough room in the case to store a plastic bag large enough for the case and the microphone I use.
By the way, the box is an old storage case for 5 ¼ “ floppy disks that was provided by a freeware/shareware distributor at some point in the mid 1980's. I'm certain there are better cases available. This one didn't require power tools to cut so I still have all my fingers.
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The parts were easy to obtain and inexpensive. Here's what I used.
2 capacitors (my first version used Electrolytic 1 uF, the second version used 2.25 uf Polyester non-polarized capacitors)
1 resistor (221 ohm, ¼ watt, 1%)
1 resistor (562 ohm, ¼ watt, 1%)
1 right angle mini stereo jack
1 female XLR panel mount connector
bits of wire, perf board, solder etc.
foam to hold MD recorder in place
A 2-Dcell batter holder
A miniplug clipped from the auto-charger that came with the MD.
The most expensive item was the XLR connector that I bought at Radio Shack for under $5.00. I know there are fancier ones but this one is such a huge improvement over the miniplugs that I don't plan on exchanging it any time soon. The resistors came mail order in rolls of 100 for $3.00, which was quite a deal since 4 or them would have cost $3.00 at Radio Shack. Even without the mail order, everything could be bought from Radio Shack for about $10.00. The capacitors in my second version seem to be less generally available.
The instructions for assembling the electrical bits are here and came originally from http://www.megalithia.com/elect/mdmicatten.pdf as posted by stoatwizard (YahooID) to Nature Recordists on Mar 8, 2007 .
Earlier, I'd posted that I was not certain that the capacitors are the correct ones, but they seemed to work. Later, I switched capacitors on the advice of Rich Peet. If you're using polarized (eg. electrolytic) capacitors and are a real beginner like me, note that electrolytic capacitors have an intrinsic polarity. In the attenuator scheme the “+” side of the capacitor goes towards the MD recorder. The capacitors I got weren't labeled “+” and “-” but a conspicuous stripe is said to indicate the “-” connection and the longer of the wires on the capacitor is the “+” connection.
As always, I'd be grateful for corrections and suggestions for improvements.
The box and the cable work very well; I used the setup for several hours this morning recording Northern Cardinal songs. Once I was saved from bad clipping by having the lower volume channel. It was a windy day with lots of man-made noise but I couldn't hear any problems with the recordings that I cold attribute to this set up. And I especially like the box because it lets me shove the recorder under my arm while one hand holds the parabola and the other holds binoculars to let me look at what I'm recording.
The real bottom line is this display from Audacity showing the first recording made with the mic attenuator:
Since first posting this page I've learned that I could have made a better choice of capacitors.
Another point that I needed help with is what to do with the three parts of the XLR connector. Originally, I connected XLR pin #2 to to the 'tip' and 'ring' inputs on the miniplug and connected XLR pin #3 to the ground of the miniplug. Because I was unsure of what to do I also tried connecting both pints #1 and #3 to the ground and couldn't detect any difference. Now I've learned that XLR pin #1 is Ground and pins #2 and #3# are the two elements of the balanced line, so they both carry signal, but they're out of phase. My understanding is that XLR pin #2 gets connected to the thing leading to the 'tip' and 'ring' of the miniplug, XLR pin #1 gets connected to the ground, and XLR pin #3 gets connected to the ground as well (or to pin #1, which amounts to the same thing).
