whaley@uiuccsb.UUCP (07/09/83)
#R:ut-ngp:-39700:uiuccsb:5900002:000:1152 uiuccsb!whaley Jul 8 13:26:00 1983 Resistance of "real" or "expensive" headphones is often 600 ohms. It is possible to buy transformers to convert the audio to 8 ohms for regular stereo phone for under 2 dollars if you know where to look. What I have done is go into radio shack (a place I don't recommend, as they usually sell very inferior stuff), and look at their audio transformers. They sold one at one time that converted 1000 ohms center tapped to 8 ohms. It was intended for push pull transistor amplifier output coupling. (If you don't understand that, don't worry.) I used the center tap with one end connection, getting half the 1000 ohms, or 500 ohms. That is close enough to 600. 8 ohms isn't close enough and can damage the aircraft audio panel. On a Grumman tiger an 8 ohm earphone caused one radio to break into oscillation, while the other was unaffected. 600 ohms is quite standard for some types of application, and there are real 600 ohm to 4, 8, and 16 ohm transformers. The one I bought had the advantage of being small and cheap; it was so small I taped it into the patch cable I had made to go from the 1/4 inch phone plug to the 1/8 stereo phone plug.
larson@sri-unix.UUCP (07/19/83)
#R:ut-ngp:-39700:sri-unix:4000009:000:641 sri-unix!larson Jul 9 01:32:00 1983 I have used Koss PRO-4AA and now use Koss K-6 stereo headphones. Both have good noise blocking character. Neither has hurt the radios in any discernable way in several years of use. The radios probably have an easier job since I don't have to turn them up as much. The noise blocking is an even greater benefit -- it makes it easier to hear, and the headphone quality is much better than the speaker. I would not recommend transmitting the comments over the air. An intercom would be a much better choice -- they will provide automatic voice detection and override of the music from the pilot and many other wonderful things. Alan