• How To...Adapt Aviation Headsets To Computers

    Adapting an Aviation Headset to Your PC Sound Card

    By Alan D. Bryant

    With the emergence of applications such as Roger Wilco, and their rapid acceptance by the flight sim community, there's suddenly a demand for decent headsets you can use with these apps during simulated flight. As a licensed pilot, I have three aviation headsets for my use as well as the use of my passengers. It seemed only natural to want to use an aviation headset during my flights, depite the fact that I look, and feel, like a complete and total geek in doing so. That's okay, though, I recognize that I'm just an overgrown kid with a lust for toys (that as an adult, I can now afford).  :-)

    While I have some basic electronics knowledge, I know only enough to be dangerous, and I had no idea if an aviation headset could be adapted to a PC sound card, and if so, how. Some basic poking around revealed an impedance mismatch between the headset and the PC audio output, and I thought that was about it other than physical connection issues. I wasn't sure, though.

    On a whim, I sent a message to the David Clark Company, manufacturer of some of the best (if not the best) aviation headsets on the market. (The headset I use, an H 10-13 S, is outstanding, and I can recommend their products very highly.) I received a response the same day, with the phone number of one of their engineers. I called him.

    While I was on the phone, he described the issues, and walked me through sketching a circuit that should work. I built it, and it does work (quite well, in fact). I relay that information to you here.

    The Issues

    Output (Hearing With the Headset)

    On the output side, there is indeed an impedance mismatch. The result is that the audio levels coming to your headset may be somewhat lower than you'd like. Perhaps, but the results in my case were superb. Compared to a cheap multimedia headset, the audio level on my David Clarks is actually higher than the cheap $15 set, not lower, as it should have been. I had to turn the volume up full blast to hear okay on the multimedia set, but can leave it at its usual speaker level when using the David Clarks. Your mileage may vary. If it's low, turn up the volume.

    Also on output, there are either minor, or no, physical interface issues depending on what you use. The 1/4" plug on a (stereo) aviation headset is the same as any stereo headset you might use, and using a simple 1/4" to 1/8" stereo plug adapter from Radio Shack, you can plug them right in... That's assuming that you have a stereo or stereo-compatible aviation headset.

    Of the three headsets I own, two are stereo and one is mono. The mono model, an Avcomm AV-200, has a stereo plug on it, and is apparently stereo compatible. The audio I hear is monophonic, indeed, but using it apparently doesn't damage anything or cause connections to be shorted out.

    If you have a headset with a two-conductor plug on it, then you'll need a different adapter to make it work without shorting one channel of your PC's audio output (something I wouldn't recommend doing for long periods, if at all). Radio Shack can probably supply an adapter for this purpose. Since I didn't need one, I didn't investigate the options. I'm sure you can figure this out on your own if this applies to you.

    Look before you plug. Again, a two-conductor plug connected to your stereo audio output on your PC will cause one channel to be shorted to ground, and may very well cause permanent damage to the sound card. (It's unlikely, but very possible, especially at high volume levels.)

    Input (Speaking With the Headset)

    On the input (microphone) side, we have some issues. First, physical. The standard in aviation is a .210" diameter plug. This plug is used in telephony and military applications as well, but a jack to fit it is not something you'll find at Radio Shack.

    The only jack I could find for it is manufactured by Switchcraft, and it's their part number S12B. It's a 1/4" stereo jack, but with a .210" bushing to ensure it mates with the plug. You can purchase these from Switchcraft dealers, including Mouser Electronics. Mouser has online ordering, and stocks the S12B jacks. You can probably order the other parts you'll need (which I'll discuss in a moment) while you're there.

    As described by David Clark, aviation headsets use an amplified electret microphone, while PCs are expecting a non-amplified mic. This causes a couple of ripples:

    • First, the PC sound card probably can't (or won't) deliver the necessary current to drive the amplification in the headset's mic. Apparently there is little standardization, however, with voltages and current supplied by a PC sound card to the mic jack, so one option is to try connecting it directly, and see if it works without any additional circuitry. In my case, it didn't.

    • Second, assuming it does work (or works with the circuit I'll describe below) the level of the audio fed to the mic jack will pack a punch (since it's amplified, duh!). I don't think this is a bad thing. If you've got a sound card, you've got a mixer applet, and you can merely control the audio level in the PC. In my case, using the cheap multimedia headset, I had to turn the "boost" feature on (something my sound card supports on the mic input), and still had to crank the level in the mixer, in order to send loud enough audio. With my David Clarks, once I got them working, I turned off boost, and set mic at a normal level.

    Assuming it doesn't work directly connected, we can fix both problems with a single, simple circuit to power the mic and isolate the additional added power from the PC's sound card. The engineer at David Clark walked me through this, and I present it here in schematic form for you.

    The Schematic

    Here's the circuit that the engineer supplied me. All the parts, with the exception of the jack, can be obtained cheap at a Radio Shack. But if you're going to order the jack from someplace like Mouser, then you can get the rest of what you need there as well. You'll probably need to order a catalog, or peruse the one online at their web site, to find everything. Notes follow the schematic.

     

    adapter.gif (36881 bytes)

     

    That's all there is to it. Here's a recommended parts list:

    • (1) Switchcraft S12B 1/4" stereo jack w/ .210" bushing (Mouser Electronics, among others)
    • (1) 470 ohm resistor (Radio Shack, etc.)
    • (2) 22 microfarad, 35 volt electrolytic capacitors (Radio Shack, etc.)
    • (1) 9 volt battery clip (Radio Shack, etc.)
    • (1) 9 volt battery of your choice
    • An appropriate project box to mount it in
    • Some sort of physical interface to the PC sound card (see below), may involve more parts

    Since it was easiest, my interface to the PC sound card was to use a 1/8" mono jack (Radio Shack), and a patch cable with 1/8" mono plugs on both ends (also Radio Shack). I mounted the circuit in a small box, drilled holes and mounted the jacks in it. Then when I want it, I just pull it out, plug in the headset mic plug and the patch cable to the box, and the other end of the patch cable to the PC's mic input, and that's that.

    Other Thoughts

    Here's some other miscellaneous ramblings.

    • USE THIS CIRCUIT AT YOUR OWN RISK! While it works for me, neither I, nor David Clark Company, accept any responsibility for your use of this information or provide any guarantees or warranties of any kind. (I can't speak for David Clark Company, really, but I'm sure they'd agree.) The potential exists for you to damage your headset and/or your PC and/or your PC's sound card in the process of playing around with this. While that's exceptionally unlikely, it's possible (especially if you screw something up on your own), so proceed with that understanding, and exercise due caution.

    • I've tested this circuit with a David Clark headset, as well as one model of Avcomm headset, and both work well for me. Your results can, and probably will, vary.

    • If you test this with PC speakers, and have them up loud, expect the loud screech of acoustic feedback. TURN DOWN YOUR SPEAKER VOLUME BEFORE YOU TEST IT OR USE IT FOR THE FIRST TIME! As mentioned above, the level of audio output from the mic is quite high. You'll probably want to lower the mic setting in your mixer applet as well before the first use.
    • For the intuition-challenged among us, plug this into the microphone input, not your line input, on your PC sound card. The levels are wrong for line in, and in addition, line in is stereo and this thing is mono, so you'll be shorting out the line inputs on your sound card (probably not a great idea to do for long periods).

    • You don't need a power switch for this. To "turn it off," just unplug your headset, which will open the circuit.

    • My drawing includes an illustration of the pinouts of the plug on the headset. The David Clarks are just as illustrated, with a "guard" band around between the tip and ring. This has no connection. Your headset may not have a guard ring; neither of the two Avcomm sets I own do.

    In Closing

    I hope you enjoy using your aviation headset for audio communication in your flight simming adventures. And I take some amount of joy from the thought that I won't be alone in looking like a completely aviation-obsessed geekoid by plugging rudder pedals, a flight yoke, and a $300 headset into my PC for simuflight... Although I confess they're all a good match for the Flight Guides, WAC charts, and sectionals that seem to spend as much time by the PC these days as they do in a real cockpit...  :-)

    (Geek, thy name is me.)

    Have fun...

    Copyright © 1999 Alan D. Bryant, All Rights Reserved