DAT and Binaural Recording

Power Options for the Sony D3 DAT

Making a D3 Battery Pack

The original snap-on battery pack for the D3 uses pretty weird, thin rectangular nickel cadmium batteries, wired in series. Typically what happens is one cell eventually goes bad - causing the whole pack to lose charge too quickly. I didn't have any success locating the original cells, and usually if one goes the remaining cells are suspect too. So, I came up with the following procedure to make a replacement pack, using the casing of the original one. What you first need to do is to saw off the top of the pack with a fine razor saw. You can find these saws at a hobby shop. Saw it off right near the edge - I think there is a recessed line already there for you to follow. Don't saw into the battery itself - just the plastic casing. Once that's done, lift it and disconnect the wiring from the batteries. Then obtain five sub-C cells of either Nicad or Nickel Hydride variety. The Nickel Hydride cells have much shorter shelf life between charges but more ampere-hours (AH) for power on demand after the charge. As a result, they will cost you more to obtain. Pay attention to the AH rating on the cells you buy. They all look the same and they can vary widely - the higher you find the better. Sources for these batteries include battery houses listed in your phone book, amateur radio swap meets and magazines, and hobby shops catering to radio control electric planes and cars. You then wire these batteries together in series - some have solder tabs, some don't. Those that don't will require you to solder wires or thin lengths of brass or copper between them. You need a hot soldering iron for this - but you don't want to get the battery too hot or it could be damaged (and maybe even explode). I wrapped the 5 cells with tape and hot-melt glued them to the underside of the case. Then you get a piece of heat shrink tubing big enough to cover the whole assembly and shrink it down. You can get this heat shrink tubing at hobby shops that might be making custom battery packs for RC cars. Finally, just trim around the contact area as shown in the photo and you're done! Note that the battery is expected to be 6V while the aux. power jack expects to see 9V.

This pack seems to charge ok with the original charger. With Nickel Hydride batteries you need to be careful not to overcharge - so don't leave it on longer than necessary. If you don't have a charger, research the subject on the net. There are several approaches to a charger solution - an RC car battery charger, a DC power supply with a series current limiting resistor, or an intelligent voltage sensing unit.

A Lead Acid 12V Battery Supply for the D3

As you can see, I made up a pretty neat package that contains a linear voltage regulator to drop the 12V down to 9V, a collection of jacks to accept mono and stereo mic setups, a power switch, and a 9V supply to power electrets plugged into one or more of the jacks.

It turns out that the D3 fits nicely in a "pocket" camera soft case. Mine is a LTX series by Tamrac. It has a pocket on the top that accepts the power and mic connection box. I installed left, right, and stereo input jacks as well as an in-line style stereo jack. I found that the panel-mount jacks are junk - they don't make reliable connections. So I mainly use the in-line stereo jack. I use a double pole double throw switch for activating both mic power and D3 power. I use an alkaline 9V battery (in the box too) to power the stereo mics via a series resistor to each and then AC-coupling the output of each to the D3. You will need to experiment with the value of the resistor you use for the particular mic you use, as this resistor also sets the mic gain. The value of the AC coupling capacitor affects the low frequency response. Mine are probably larger than they need to be, but I would rather EQ the lows out than not have them there to begin with. It would be useful to have a switch to change this if desired.

For the regulator, I used an LM317. Nothing abnormal about the use of this - it is right out of the datasheets. I set a trimpot to get 9V out, then measured the value of the trimpot and replaced it with resistor(s) of that value. I stuck a little heat sink on the LM317 to help dissipate the heat. You need a minimum of 3 volts more on the input than desired for the output voltage. So a 12V battery works out well.

I typically use 12V 7AH lead acid batteries for the main power source. I place one of these in a belt pack and can usually get at least 2 days of use at air races I record.

Binaural Recording

Making Your Own In-Ear Mics

If you are just beginning with a DAT, you have to buy a few of these and give them a try! I have had good luck buying them surplus from the likes of All Electronics. Digikey is a good source for brand new Panasonic electrets.

Electrets require a resistor-fed power source. The output signal is AC coupled to the recorder input by a series capacitor. The value of the resistor sets the gain of the electret as well. You might want to start with 2.2K for the resistor and 1uf for the capacitor.

There are mods individuals perform on the electrets to achieve wider dynamic range or better frequency response; like modifying the front hole diameter, or sealing the rear of the module with epoxy. I haven't tried any of these. I'm more interested in comparing various models and understanding the differences between each. I haven't been able to see these differences as accurately with a software package as I can hear with my own ears.

So, anyway, be on the watch for stereo headphones or a stereo extension cable that goes for under $1 or so at a swap meet. These make perfect wiring for your in-ear mics. Wire them as necessary for correct polarity, maybe color code them so you know which mic is which channel. Then you have several options as to how to use them:

They can go in your ears as is.

They can be encased by earplug material and inserted in your ear.

You can obtain prosthetic ears and insert the mics in them.

You can forget about ears and mount them to your glasses arms or something.

If inserting them in your ears, you want to use mics that will fit ok, plus you don't want to insert them too far. You also don't want to cut your ear canal in any way as this is a great area for infection to occur. There are swimming earplugs that you can modify to surround the mic and protect against infection etc.

I purchase a couple prosthetic ears from an audiologist supply house (Westone Laboratories, Inc. 1-800-552-7203) for around $30 or so. These are intended to act as "dummy" ears for learning to make ear impressions (part #157-A). These seem to work great for "remote" ears for recording purposes! Really fun to play with. Purists will tell you there is more to the binaural effect than just the ears but these sure get you close.

Many say that binaural recordings have a bunch of phase distortions in normal speaker playback that become objectionable. They recommend mics placed near the ears to reduce this. I prefer to use headphones to get the full effect of the in-ear recordings so I continue to record that way.

email me: barry.l.klein@wdc.com created 5-5-99

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