David clark aviation headset - HomeBrew Forum at eHam.net

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David clark aviation headset	Reply
by KC0ILV on October 8, 2005	Mail this to a friend!
I was lucky enough to find a david clark military aviation headset (h10-76) with a civilian mic on ebay. (the military headset is needed because the headphones are 8 ohm impedence, and the civilian mic is needed for it's high impedence) While the headset works beautifuly, the mic dosen't. If I put a lot of sound into it, then I get some output, but otherwise, there is no output. The manual says that I need to supply a 5V DC bias voltage in order to get the mic to work. I know that my Yaesu has a 5v supply on the mic jack, but how can I supply this to the mic?

RE: David clark aviation headset	Reply
by KC0ILV on October 8, 2005	Mail this to a friend!
Ps: I have tried to connect the 5v to the mic, but it does not help output, and I get a little 'tick' noise about once per second, which I believe is from a voltage regulator circuit.

RE: David clark aviation headset	Reply
by AA4PB on October 10, 2005	Mail this to a friend!
I don't have any info on this particular mike but it sounds like an "electret" considering the need for a 5V bias voltage. Generally the +5V is applied via a resistor from the +5V supply line to the audio line. The value of the resistor depends on the impedance of the mike but should not be too critical. I'd guess something on the order of 1-2K would be a good place to start.

RE: David clark aviation headset	Reply
by AA4PB on October 10, 2005	Mail this to a friend!
I don't have any info on this particular mike but it sounds like an "electret" considering the need for a 5V bias voltage. Generally the +5V is applied via a resistor from the +5V supply line to the audio line. The value of the resistor depends on the impedance of the mike but should not be too critical. I'd guess something on the order of 1-2K would be a good place to start.

RE: David clark aviation headset	Reply
by AA4PB on October 10, 2005	Mail this to a friend!
I don't have any info on this particular mike but it sounds like an "electret" considering the need for a 5V bias voltage. Generally the +5V is applied via a resistor from the +5V supply line to the audio line. The value of the resistor depends on the impedance of the mike but should not be too critical. I'd guess something on the order of 1-2K would be a good place to start.

RE: David clark aviation headset	Reply
by N3ZKP on October 10, 2005	Mail this to a friend!
Have you tried dropping Clark a note and ask them?

RE: David clark aviation headset	Reply
by KC0ILV on October 10, 2005	Mail this to a friend!
I have not yet contacted DC, I looked on my mic, and it turns out, it isn't even an electret, it is instead a dynamic, and so it dosent require a voltage. sry, my mistake. The issue now is impedence, the mic is about 100 ohm, and the radio expects 300-10k ohms, so I will need to figure out a transformer or preamp to match the mic to the rig thanks for the help KC0ILV

RE: David clark aviation headset	Reply
by K8AC on October 15, 2005	Mail this to a friend!
A couple of years ago, in a June or July issue of QST, there was a very good article about converting aircraft headsets to ham use. It included how to deal with the electret microphone power and impedance mismatches. If you search the ARRL site, you'll likely find it. Just before this article came out, I converted a new Flightcom headset to use with my Icom 781 and it's worked out great for contesting. If you can't locate the article, let me know and I'll try to find it for you. I no longer have the QSTs, but can probably locate it on the website.

RE: David clark aviation headset	Reply
by WA2UNN on October 21, 2005	Mail this to a friend!
Many military type dynamic mikes have very low output (millivolts) try feeding it into the phono input of an old hi fi amp and see if the mike is working. If it is just use a low noise op amp chip to provide the extra gin to drive the transmitter. I you have access to an oscilloscope you can measure the output voltage of the mike Any questions....just let me know wa2unn wa2unn@aol.com (for a few more days)

RE: David clark aviation headset	Reply
by KB1GMX on October 23, 2005	Mail this to a friend!
I have three avaition headsets, two are David Clark and the other is TELEX. DC FYI has fantastic service. First the headphones are medium impedence (100-600ohm range) so that should present any big problems. The mic side varies. One DC I have is carbon, the other is electret and my Telex is also eletret. To power the mic for any of those 5V through 1000 ohms to the mic will do fine. Polarity matters for electret, carbon doesn't care. Dynamic mics are not as common in general avation. Most aircraft radios expect a carbon mic or equivelent such as a dynamic mic with amplifier or an Electret element. However a simple transistor amp can be made up to translate plain dynamic to look like carbon or electret. OR you can order a replacement electret mic from DC. It can be hard to tell whats what with an ohm meter. However if it emits a click when you touch the ohm meter to the mic leads it's dynamic. I've used two of the three for ham use, the carbon has a poor sound quality. Since my radio assumes an Eletret mic the interface was connector adaptors only. Allison KB1GMX

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