OT: Anyone of you guys good with electrical circuits?

From: Lynn Dixon 
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I have a pretty nifty project that I have been thinking about doing, but
its a bit out of my electrical circuit knowledge.

In a nutshell, I would like to mod one of my 5.25" bays on my PC to house
jacks that I can plug my aviation headset into.   There is a pretty good
difference in impedance between aviation headsets and PC audio.  There is
also a challenge in driving the electret mic in the headset using the PC
mic input.

Bonus:  If I can plug this modded panel into my motherboards front panel
audio input, that would be awesome.

If anyone of you guys are good with basic electrcal circuits give me a
shout.  I can spring for dinner / beer if your willing to help.  Hell, I
will even be president for a Chugalug meeting if we can get enough folks
together to discuss this :)

Sorry for the off topic post to the LUG.

=============================================================== From: Jason Brown ------------------------------------------------------ So you want mains (110v-120v) standard 3 prong electrical outlets in a 5.25" drive bay? Possible, but might introduce some noise, it also might not. There is risk involved, but mostly to your computer equipment. If there is every a short to your case your computer is toast and most likely every thing in it and attached to it. Since you have limited electrical knowledge I would recommend this route: Buy a cord like this one: http://www.sears.com/shc/s/p

=============================================================== From: Phil Sieg ------------------------------------------------------ Errr Jason, I am not sure where you got the idea Lynn wanted and AC = power plug on the front of her PC? I read her meaning as a couple of 1/4" phono jacks(?) for an aviation = headset that works at funny/different impedance than standard pc audio = amplification. This is what came to mind for me: = http://www.crutchfield.com/p

=============================================================== From: Joe Freeman ------------------------------------------------------ I would think that a couple of 1/4" bulkhead jacks mounted in a 5.25" filler plate, with a small piece of perf board and a few components would do the job. Here's the circuit for the microphone impedance match (and power) - http://www.flightsim.com/vbfs/content.php?1985 Or you can replace the 1/4" jacks on this - http://www.aircraftspruce.com/catalog/pspages/pilotUSA40.php?clickkey=17252with bulkhead jacks on a 5.25" spacer plate as I mentioned before, if you don't want to build anything. Joe

=============================================================== From: Jason Brown ------------------------------------------------------ I think I misunderstood "House Jacks".... --Jason

=============================================================== From: Lynn Dixon ------------------------------------------------------ Phil, That's what I am referring to. I am not sure how household AC current got mixed into it.. hehe. Aviation headsets have two jacks. the first is a 1/4" for speakers in the headset (my David Clarks are actually in stereo, most are just mono). They have a pretty high impedance when compared to the headphone output of a PC. Some people have had decent luck just getting a 1/8 to 1/4 adapter and turning up the volume on the mixer panel in the PC. I would rather have the impedance matched somehow. The second jack is an odd ball size. Its a bit smaller than a standard 1/4" jack. Its right at .205" this makes it easy to plug your headset into the proper panel jacks in your airplane. Each plug only plugs into its proper jack on the airplane panel. But, I have bought a couple of the right mic jacks from Aircraft Spruce in Atlanta. So, I have the jacks I need. However, the mic in most aviation headsets are electret because they work in loud environments (most GA planes are really noisy). I have found this in my googling: http://www.flightsim.com/vbfs/content.php?1985 It has a good schematic for the mic, and how to drive it with a 9V battery. But it would be awesome to be able to plug into the Front Panel audio header on my motherboard and then mount the jacks themselves in a 5.25" panel on my PC. the AC'97 headers have a 5v supply and mic in and headphone out, but I would need to match impedance. In the schematic, there is a 470 ohm resistor on the 9v battery, but I am not sure what that would bring the voltage to, I doubt its 5V so that might eliminate the 5v from the AC97 header.

=============================================================== From: Stephen Kraus ------------------------------------------------------ Lynn, I have the jack you are looking for, if its the same as the military jacks. Should be called a U92 or U94

=============================================================== From: Lynn Dixon ------------------------------------------------------ Stephen, Awesome, thanks for that! I did buy 2 of the switchcraft jacks from Aircraft Spruce that are panel mount for the mic input. I am just trying to wrap my head around matching the impedances for the speakers as well as driving the mic circuit with the 5v feed from the AC97 header. I could always use a molex and step the 12v down to 9v, but it would be nice if I could just use the 5v coming from the AC97 headers. Do you have any of those U92 or U94 jacks on hand? If you do I might pick some up to tinker with.

=============================================================== From: Stephen Kraus ------------------------------------------------------ The only difference between the U94 and U92 is the switch for PTT which is wired in, I can get you pin outs when I get home

=============================================================== From: Dan Lyke ------------------------------------------------------ On Fri, 8 Feb 2013 10:40:50 -0500 Lynn Dixon wrote: How much current does the electret mic want? Seems like you should be able to just reduce the value of the resistor in Joe's circuit. In fact you could probably just start with a 470 Ohm resistor, and if that doesn't drive the mic then step it down. If not then, yes, I'd just hang a 7809 regulator off the 12v of a drive power connector. Fascinated to hear how this works out, because one of the things Charlene and I have talked about is an aviation headset for the workshop, so that I can talk with her in the house while I'm out in the shop. Dan

=============================================================== From: Joe Freeman ------------------------------------------------------ You could prototype with a 1Kohm pot in place of the resistor. Just put the battery positive on the wiper, and use one of the other leads for the circuit. Turn the pot till things work well, pull the circuit and measure for the correct value.