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Thread: Getting More Volume from a Handheld Radio

  1. #21
    rwanttaja's Avatar
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    Quote Originally Posted by Sam Buchanan View Post
    Headset volume has been a problem in my very windy and noisy Fokker D.VII replica. I use a Yuasa handheld and Lightspeed QFR ANR headset but still have problems hearing some radio transmissions.

    Until today. Following Ron's suggestions, I ordered the 42TL004 miniature audio matching transformer from Mouser and wired it onto the headset adapter. Wow...lots more volume! I was a little concerned about proper matching because the transformer input is 10 ohm and the radio specs say audio is fed to a 16 ohm speaker. But it seems to work fine and I hope there are no long-term issues with the small mis-match.

    Highly recommended mod and much appreciated!
    Glad it worked for you, Sam...and appreciate the feedback. I'm trying to get the word out as much as I can...I'm finishing up an article for Kitplanes on the subject. As part of it, I've been on an adaptor-building binge, trying out a number of different approaches.

    For those who would like to try this out with minimum effort/minimum cost, here's what you can do: Start with a 1/8" to 1/4" earphone plug adaptor. These allow plugging standard consumer-grade headphones (with a 1/8"/3.5mm plug) into the standard 1/4" headphone socket. They usually come with upscale headphones, or you should be able to find them at places like Best Buy. They sell online for as little as a buck.

    Using a drill, put a slight dimple in the insulation between the tip and the first ring. Then use solder to bridge the tip and first ring. Sand down the "bump" from the solder so the plug will still enter a jack.


    This converts the adaptor to mono...puts the same audio signal into both the left and right channels.

    Now: Take an ordinary set of ear buds and plug them into your handheld radio, using the adaptor. You should be notice one heck of a lot more volume.

    If you want to try it out in flight, just put your regular headset on over the ear buds, and insert the microphone plug into the headset adaptor. Use tie-wraps or a bit of tape to keep the unused headphone plug out of the way.

    You can try this out WITHOUT modifying the adaptor, but you'll have only one ear bud working.

    Now, if one has an intercom in the airplane, it's likely you've been able to use the intercom's amplifier to crank up the volume to overcome the mismatch. But I heard from a gent in California who had problems with the levels...with a second headset plugged in, the engine noise would be picked up by the mikes and played over the headsets.

    He put the impedance matching transformer between the handheld and the intercom, and the problem went away...he didn't have to run the intercom volume so high.

    Ron Wanttaja

  2. #22
    lnuss's Avatar
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    Nice, Ron. But note that they also make adapters that preclude the need to modify like that: Here is a 3.5mm stereo to 1/4" mono adapter, for example.

    Larry N.

  3. #23
    Jim Heffelfinger's Avatar
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    Well, after converting the speakers I was trying out the auxiliary jack - nothing coming through. Head scratching - it sat on my bench during the week as a reminder I was stumped. I was trying to figure was it a mis-match in impedance? a broken wire, a shorted jack. There was a 56 ohm resistor across the input. Is it shorted? Since the seller did not have a wiring/schematic diagram I started to trace out on my own. This is not rocket science and we are talking audio frequencies here. I pulled out an ohm meter.... Hum the wires to the PWB/PCB were correct but the ones at the jack itself were reversed - shouldn't matter in this case but I fixed it....checked again - nothing. I pulled out some jumper cables and started to check out the paths jumpering directly to the speaker pads on the PWB. Ta - Da audio. Plugged it back in to the jack - Na-Da. Okay jack shorted - nope, Jumpered to the input pads - Na-Da. Back to my drawing - resistor shorted - nope _ silence. I was so locked up in the impedance mismatch - now 4 ohms ( 8s in parallel) v the 150 (300 in parallel) that I missed a humbling troubleshooting error. I made an assumption. Here is the PWB - can you see the problem???
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    Last edited by Jim Heffelfinger; 05-28-2017 at 03:35 PM.

  4. #24
    rwanttaja's Avatar
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    Jim, I finally remembered to bring my converted RA200 home to do a little experimentation.

    I plugged my cell phone into the ("hey, there's a 3.5mm jack here") headset. It worked, but at an extremely low audio level. I had to crank my phone volume up all the way to hear it, getting all sorts of warnings about danger of hearing loss, etc. Even at that, it wasn't very loud. If I hadn't been sitting in my workshop (a shrine to gadgetry, with the appropriate solemn hush and candles burning low in the sconces) I might not have been able to hear it.

    They obviously put that 56 ohm resistor in there to attempt some sort of matching to 300-ohm speakers, and possibly, to help act as a mixer. I wonder if that's what's messing you up with the 8-ohm speakers in place? You have, essentially, a 56-ohm minimum on the volume control.

    Just shorting out the resistor will do the trick. The only thing is, I'm not sure that that does when the aircraft radio and your tunes device are then basically connected directly in parallel.

    Ron "What's burning?" Wanttaja

  5. #25
    Jim Heffelfinger's Avatar
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    Nope, you didn't find the error. Hint green is common...........

    I'm going to let this sit for a day or so - somebody will catch it.
    Last edited by Jim Heffelfinger; 05-28-2017 at 11:12 PM.

  6. #26
    Jim Heffelfinger's Avatar
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    No takers.....Maybe this will help.

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  7. #27
    robert l's Avatar
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    OK Ron and Jim, this may not be rocket science but to some of us it's still Greek. Plug the Frugal Shaft into the Thngabob then cross dress the Turbo Incapulator ! Say What ??? I finally figured out some years ago that I'm a visual learner. You can describe it to me, I can read it 47 times and still not get it, especially with electronics. I have an older I-COM but have never used headphones with, I generally just listen to the AWOS while sitting in the truck waiting for my appointed flying time. But this is very interesting.
    Bob

  8. #28
    DaleB's Avatar
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    I can see why it doesn't work. I just can't figure out how it ever did work.
    Measure twice, cut once...
    scratch head, shrug, shim to fit.

    Flying an RV-12. I am building a Fisher Celebrity, slowly.

  9. #29
    Dana's Avatar
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    How could that board ever work?

  10. #30
    Sam Buchanan's Avatar
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    Quote Originally Posted by Dana View Post
    How could that board ever work?
    The signal wires must be crossed somewhere else in the headset. Reminds me of the old British car's wiring....purple wire plugs into green, yellow into red, etc, etc......
    Sam Buchanan
    The RV Journal RV-6 build log
    Fokker D.VII semi-replica build log

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