David Clark headsets can be bought relatively cheap on eBay, and especially the military sets H10-76 and H10-76XL. Why these sell so cheap we will not investigate too much, but it is possible to think that these headsets are standard equipment on the U.S. military, and that many sell them after their service in the military is over.
Acousticom offers a 10% discount on all their products if you click on the link to the left of the main page with the text Coupon IMFK, Acousticom.com. Please note that orders which are not made through this link, will not automatically give a discount.
Right now it is possible to save even more money, since Acousticom has given us a special discount for conversion products to the David Clark headsets discussed in this article, via coupon codes.
Coupon Code: h1076 (15% discount on all products during the conversion kits) Coupon Code: 5bucks ($5 discount on all electret microphones sold acousticom.com.) Coupons are unlimited in time, but are valid for one purchase per customer with coupon h1076. The 5bucks coupon is only for two microphones per customer.
This means you actually can get a quality headset for a price as low as $100. And since the H10-76 has a suggested retail price ay $280, this is a good value for money way to get good equipment for your aircraft.
The difference between H10-76 and H10-76XL is quite big, XL version have electronic noise reduction. Electronic noise reduction comes under many names, we have seen various names as ENC (electronic noise cancellation), ANR (automatic noise reduction) and more. For David Clark, it is the sets marked with XL which are are equipped with electronic noise cancellation. This means that there are microphones and speakers inside the headset that picks up the noise and send it phaseshifted back into the ears. And for the ones knowing how a radio work, we know that the same wave, where the phases are inverted, zeros out each other. Passive nose dampening with insulation is around 27 dB for this headset. For the XL model with ENC, there might be up to 49 dB attenuation.
If you're wondering how this works, you can see a pretty good explanation in this video:
There are some important issues to note when it comes to headsets. In broad terms there are two types of headsets on the market, one for military use, and one for general aviation. Military headset has low impedance microphone and speakers, while the GA sets have high impedance microphone and speakers.
Military headsets usually have two 19 ohm speakers connected in parallel providing around 10 ohms. Which compared to the speakers in GA headset equipped with speakers between 300-700 ohms is a little different. In addition to this, the microphone used in the military headset is 6 ohms, opposed to the microphones in GA headset which is about 50. If you plug a military headset into the intercom in private aircrafts, you will hear well, but the sound from the microphone is missing.
In a very simple way you can sum it up like this: Military headsets have a microphone which is not compatible with the intercom to general aviation, and speakers which are not optimal.
Another thing to note is that the helicopter and GA have different connection plugs to the intercom. GA has one jack for microphone and one jack for the speakers. While the helicopter has one plug for all these features. For the helicopter, the plug is called either the Nexus plug, U.S. NATO plug, U-174 / U or TP-101. This is a short plug with four connector rings.
The left photo shows a standard helicopter plug that will not fit in a GA or a microlight aircraft. David Clark's H10-76 and h10-76XL are equipped with such a plug, and you have to replace that plug or use a converter. We have tried both and have concluded that changing the plugs gives the best result. A converter needs space and static from poor contact can often be heard.
The military connector shown on the left have the following key for wire connections:
One should as a precaution use a multimeter to measure which color of the wires are connected to what part of the plug to be certain. Replacing and soldering new plugs are quite easy with standard type that is appropriate for GA and ultralights. The plugs that apply to general aviation is called M642/4-1 (PJ-055) and M642/5-1 (PJ-068).
These are plugs of the size of .206 "and .25". The largest of these, we know in Norway as a standard plug for microphone as mono. Or as plug for headphones as stereo. All of these plugs are available from Acousticom, or on eBay. The wire connection is standard, with GND attached at the base of the plug, and plus attached at the outer connector for the speaker jack. GND is at the base, with the plus on the middle connector for the microphone jack.
Usually the speakers work well, even if they are of the military type of 10 ohms, It will be slightly larger power consumption, and you may find that military headset to some extent provides higher volume than GA sets if you mix them on the same intercom. We have converted several military headset and kept the original speaker elements, and it works mostly very well. Only on one radio, we have experienced a beeping tone when transmitting with the original speakers, almost like feedback.
It is perfectly possible to keep the original military speakers. Or perhaps buy a impedance converter when one need to mix military and GA headsets on the same intercom. Such an impedance converter will not work for the microphones, and they must be replaced. We have bought all of our microphones, converters, and cable/plugs from Acousticom Corporation in the United States. They are cheapest, quickest to deliver and has in our opinion a very good quality of their products. And you know what, Acousticom is a supplier to David Clark's headsets. For the conversion it is the job of unmounting a dynamic 5 ohms microphone from Acousticom, before installing a 200 ohm electret microphone also from Acousticom.
Usually it is enough to replace the microphone and connector plugs, and you're ready to use your headset. Procedures to change the microphone is described below. While the choice of using a plugconverter from helicopter to GA or replacing the plugs to the correct ones, is left up to the individual to choose.
The first step in the process is to locate the screw of the microphone. There is a phillips screw on one side and a flat-slotted screw on the other side. These two screws must be loosened completely, and removed. The microphone is then completely loose with the exception of the cord attached to it.
The next thing to do is to locate the two tiny screws that holds the cableplug to the microphone. These screws must be loosened before the microphone will come loose. The picture on the right shows those tiny screws just to the left of the text on the microphone. The screws must be loosened all the way to the final round before the microphone will get loose. After the cable is loose, the microphone is ready to be removed. If you have a headset with a wire boom, or a set with a halfflex boom, you will need the microphone of the wire boom type. You might need to drill out the hole that the two bolts go through a little bit, depending on the type of boom, and the production series you have the H10-76.
The electret microphone is of the type that it pictured to the left. In this image it is visible both the two small screws for microphone plug and the hole which you might need to bore up a bit depending on the version of headset you have.
Installation is easy, after the old microphone is removed, you just need to mount the new in opposite order. Unscrew the small screws, snap back the microphone cord and mount the microphone back in the boom.
The result should be like the picture on the right, an old military dynamic microphone to spare, and a new electret microphone in the headset. A 10 minute job!
By using a plugconversion to get the correct plugs, the headset is ready to use! Retrofitting of correct plugs are relatively easy too. By using a piece of shielded cable and two wires for soldering correct plugs for speaker and microphone. Often this will be stronger and make less noise than a plug converter. And not to mention the price, which is $13 for plugs in compared to a plug converter for $49
We have tried both and are satisfied with both the converter and soldering in new plugs. And we leave it up to the individual to assess what is best.
If you have other headsets that are GA on the same intercom as the H10-76, we have experienced that it can be lower volume on these. An impedance converter may be a solution, or you might want to do do a full conversion with new speakers too. Acousticom have their own complete sets for such a modification. If you have a military David Clark headset which you are dissatisfied with, but want to adapt it better to your intercom system, you should look a little at Acousticom's solutions for the conversion.
And as mentioned earlier, you get a 10% discount on all Acousticoms products if you click on the link to the left on the main page. This is an agreement we have been fortunate to get at least out 2011. At Acousticom you will find most what you need for rebuilding, conversion and repairing your headsets and other radio equipment. In addition, there are more discount for conversion parts for David Clark than the 10% already mentioned.