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GA to 8ohm Headphone Adapter Completed
Having posted to this group before, I though I would just provide
the follow up. I completed a transformer design - thanks for people who posted in the group with information. Instead of paying $75 - $150 for an adapter, I constructed what is the equivalent of 500 ohm source impedance to 4 ohm (actually, 2 8-ohm earbuds in parallel) adapter. I've tested the unit and am quite happy with it. I used a stereo 1/4" male adapter cable into a 3-piece PVC tube assembly (2 end caps and a 3" piece - stock off the shelf from Home Depot). I used a Radio Shack $2.99 audio transformer and using my old engineering days book, insured that I had the right impedance transformation ratio. Not including my labor (hee hee), I spent a grand total of approximately $7 in parts. In general, most aviation radios expect too see 200-ohm to 600-ohm loads. Higher loads are typically fine, but lower isn't a good idea. If one uses 16-ohm headphones or 32-ohm headphones (not uncommon at all), the load impedance seen by the radio is higher. This prevent excessive current loading, but higher will affect "optimum" power transfer. It is safe, nonetheless. The reason I did this: As an engineer and musician for a music company, I have some very high-end custom molded, in-ear headphones that I found are very comfortable and work very well in the plane. Now - I have to obtain a boom mic to use . . .that hasn't been as easy as it sounds for my "low budget" approach . . . I thought some of you might be interested to hear how I finished that up. Good flying! Gary |
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GA to 8ohm Headphone Adapter Completed
Gary G wrote:
Having posted to this group before, I though I would just provide the follow up. I completed a transformer design - thanks for people who posted in the group with information. Instead of paying $75 - $150 for an adapter, I constructed what is the equivalent of 500 ohm source impedance to 4 ohm (actually, 2 8-ohm earbuds in parallel) adapter. I've tested the unit and am quite happy with it. I used a stereo 1/4" male adapter cable into a 3-piece PVC tube assembly (2 end caps and a 3" piece - stock off the shelf from Home Depot). I used a Radio Shack $2.99 audio transformer and using my old engineering days book, insured that I had the right impedance transformation ratio. Not including my labor (hee hee), I spent a grand total of approximately $7 in parts. In general, most aviation radios expect too see 200-ohm to 600-ohm loads. Higher loads are typically fine, but lower isn't a good idea. If one uses 16-ohm headphones or 32-ohm headphones (not uncommon at all), the load impedance seen by the radio is higher. This prevent excessive current loading, but higher will affect "optimum" power transfer. It is safe, nonetheless. The reason I did this: As an engineer and musician for a music company, I have some very high-end custom molded, in-ear headphones that I found are very comfortable and work very well in the plane. Now - I have to obtain a boom mic to use . . .that hasn't been as easy as it sounds for my "low budget" approach . . . I thought some of you might be interested to hear how I finished that up. Good flying! Gary Is your intercom/radio capable of enough signal level (voltage, not current) to compensate for the ~100-1 stepdown in voltage? I took a shot at your idea several years ago but the local musician supply couldn't even quote me a price for the in-ear phones. If the custom earbuds meet your 'low budget', why not just get the mic designed to work with the phones? Charlie |
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GA to 8ohm Headphone Adapter Completed
On Fri, 18 Nov 2005 20:45:27 -0600, Charlie
wrote: Instead of paying $75 - $150 for an adapter, I constructed what is the equivalent of 500 ohm source impedance to 4 ohm (actually, 2 8-ohm earbuds in parallel) adapter. Is your intercom/radio capable of enough signal level (voltage, not current) to compensate for the ~100-1 stepdown in voltage? he has ~100:1 impedence ratio ... that will be about a 10:1 turns ratio ... impedence in an n^2 relationship. Question is still valid, though. The POWER, less efficiency, will be the same, so 1mW at (say 400 ohm) will be 1mW at 4 ohm. So if the sensitivity of the transducer elements is the same, same SPL. |
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GA to 8ohm Headphone Adapter Completed
The turns ratio is about what you mentioned.
The issue is impedance and total power delivery. You get an offset of voltage in one direction, and current in the other. The radio itself won't really need to drive any more current because it sees the impedance it wants to see. The answer is yes - it works fine. The "low cost" approach to the flight is a good question. The in-ear headphones are priecy - they ran me about $150 and are quite good. BUT! That's part of my profession in the music industry. Throwing another amount out wasn't really in the cards. I am going to purchase a mic. I actually have one, but can't get the schematics - and since it is powered, I have to be careful. I bought an old StarSet series, and can't for the life of my se the schematics - it ha a dual plug for the headphone. I'm going to remove that and just use the mic. The headphone is more for quite-cabin use. My headphones are very comfortable and have maximum isolation for "non active noise reduction" type headphones. Thanks for the follow up! Gary |
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Thread | Thread Starter | Forum | Replies | Last Post |
GA to 8ohm Headphone Adapter Completed | Gary G | General Aviation | 4 | November 22nd 05 03:03 AM |