Finished! Well, sort of, got to tidy up the wiring on the headset mounted on the IBH and find some more ferrite cores to help reduce EMI and RF interference. But everything is good to go, finally figured out how to bypass the mic, so that the amplifier only would boost the input or radio output. Along the way I learned a number of things that might help someone else in the future. Motorola Talkabout uses some proprietary 2.5mm jack, slightly longer, at a total length of 13 mm. To shim for this length, three M3 washers will do the trick on a female connector. The output is mono, with the 3 connector TRS, Tip - Speaker, Ring - Mic +, Sleeve - Ground(Speaker)/Mic -. To bypass the amplifier, route the connector that goes to the ring or Mic +, and go directly to the output 2.5mm female on the amplifier. The Comtac plug, replica Nexus TP-120, a 4 connector TRRS, is the following: Tip - PTT Switch, Ring - Mic +, Ring - Ground (Speaker)/Mic +, Sleeve - Speaker. If you plan on using an LM386 IC, the jumper or gain of 200 is overkill, go with the gain of 20.
Guts of the in-line amplifier, found an enclosure that worked nearly perfectly for the PCB, but had to remove the dual gang pot to the top, and hand fit the lid so it would close on the box. Default the amplifier is driven by a 9V battery, but I added a small tamiya plug so it can be ran by some spare 8.4v mini batteries I've got laying around that never get used any more.
Also after doing some more research, apparently people with Midland radios had an issue with their PTTs, which was resolved with the following mods, note this is separate from what I did - as my signal required amplification.
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Originally Posted by T@NK
if its not working then just go buy a new one, these ptt repo are cheap anyway
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Yeah, that's what I did, two separate ones had the same issue. The low power GRMS/FRS radio I've got, single-pin Motorola Talkabout just can't drive the Comtacs alone. However, out from the three PTTs, I'd have to say the one built the best would be the replica Nexus U94, which doesn't require a PCB board, and seems more ergonomic. After tinkering around with all the replicas, I think I can build up my own U94 PTT.
The U94 is the one on the left side. Here are the guts of a real U94 for reference and also a Peltor PTT.
Quote:
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Originally Posted by Amos
Wow.. That's alot of work for a clone headset...
If you enjoy the tinkering, then all the power to you
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No kidding, took some time too, because I really didn't have a chance to look at it, until the weekends where I'm free, the up side is I've become pretty proficient with soldering now. And have a better insight into comms, and how they work.