Mic interface box for headset

[guttapercha]

Hi project-inclined hams,
I was recently given a David Clark H10-20 headset and a box that the previous owner made to use the headset with a Kenwood TS-2000. I have an Icom 7300, and it would be cool to be able to use this. It looks like a pre-amp circuit, because there is a transistor and a transformer on the board.

The RJ-45 goes to an 8-pin female mic connector. I am hoping that I can just wire-up an 8-pin connector that I can use for the Icom.
I compared the pinout for the Icom and the Kenwood, and I'm a bit embarrassed to say that I'm confused!

Help appreciated,

Thanks,
Josh

 

[serial14]

I can only offer some hints/guesses.

I've done a lot and owned several David Clark(DC) headsets, they are great. They key question though is what microphone element is installed in it? DC offers dynamic microphones, electret microphones, amplified microphones all in the same form factor to connect to the head set boom. A stock H10-20 comes with an amplified electret microphone module, which would need to be fed power.

The rest of whats in that project box is probably dealing with interfacing the radio to the headset connector wise but also electrically for levels and such.

I'm not familiar with the TS-2000 or the IC-7300 enough to know off the top of my head what style of microphone they expect. I know with my own radios, some expect a dynamic microphone and some expect a electret type microphone and thus require different microphone levels. I would suggest starting with answering that question for the TS-2000 that it was previously used on and what your IC-7300 expects. If they both expect the same thing, I'd think a safe starting point would simply be to adapt the RJ45 -> 8 pin microphone cable to the necessary wiring. If they don't match however, you'll need to make the appropriate circuit changes.

 

[guttapercha]

I can only offer some hints/guesses.

I've done a lot and owned several David Clark(DC) headsets, they are great. They key question though is what microphone element is installed in it? DC offers dynamic microphones, electret microphones, amplified microphones all in the same form factor to connect to the head set boom. A stock H10-20 comes with an amplified electret microphone module, which would need to be fed power.

The rest of whats in that project box is probably dealing with interfacing the radio to the headset connector wise but also electrically for levels and such.

I'm not familiar with the TS-2000 or the IC-7300 enough to know off the top of my head what style of microphone they expect. I know with my own radios, some expect a dynamic microphone and some expect a electret type microphone and thus require different microphone levels. I would suggest starting with answering that question for the TS-2000 that it was previously used on and what your IC-7300 expects. If they both expect the same thing, I'd think a safe starting point would simply be to adapt the RJ45 -> 8 pin microphone cable to the necessary wiring. If they don't match however, you'll need to make the appropriate circuit changes.

Thank you so much for your thoughts. I did some homework, and here's what I found and hypothesize
1) The mic element on the DC set is the M7-A, which takes 8V DC. The ham rigs both supply 8V via a mic pin.
2) The impedance of the M7-A is 50 ohms...but both Kenwood and Icom rigs want to see higher impedence (250-600 ohms), so there must be some matching in the project box.
3) The Ham rigs also want to see lower impedance for the speakers. The DC 10-20 is 150 ohms and the ham rigs want to see 8-16 ohms, so there must also be some matching for audio out.

It's interesting that the aviation gear is so different impedance-wise from the amateur gear.

The pin outs for the mic jacks on the two ham rigs are different, but I think I figured out the equivalent pins for the mic and PTT.

The gentleman that gifted this to me hasn't played radio in several years and he is moving out of the neighborhood unfortunately. He's a retired engineer and I have no doubt that he knew exactly what he was doing. I also have his old TS-2000, so I suppose I could try that and see how it works with that rig.

 

[serial14]

You're welcome.

If you have "the whole setup", it might be worth just "double checking" that it all still works. Then you have a base line for your expectations. You can also try operating with the headset to see if you really like it. In the aviation world, there are two types of people... people that like DCs and people that don't.

I'll offer a couple observations on utilizing DC headsets... especially how it applies to ham radio. Again to help set your expectations

• DCs have a lot of passive noise attenuation. You can look at the specs but its something like 26-32dB of outside noise attenuation. This is very helpful in things like noisy airplanes, vehicles, etc. This can also be great for radio if you're operating in an area with ambient noise that you'd rather not hear. It comes at a price, people can sneak up on you easier
• DCs have alot of clamping force. This is one of the main gripes from people that don't like DCs. DC offers various ear cups to help with comfort. My personal favorite is the gel ones. For extra comfort they sell cotton things that go over them as well.
• The human mind is used to hearing your self talk. When you're wearing DCs you're ears can't hear your mouth talking as well. As a result you really have to be careful that you don't start yelling. With awareness and practice its possible to re-train your brain to overcome this and just talk normal.
  • This is probably this biggest factor in "usability" with the ham radio world I'd guess.
• To account for the above, systems that use DCs have a feature called "side tone" that puts some of the mic signal back into your headphones so that you can hear your self. On all the stock ham radios I've used headsets with, I haven't found one with side tone by the way.

Finally some commentary on your findings about impedance. You are absolutely right, aviation does it differently than ham radio. I don't know why. But I will say I haven't worried about the headphone impedance value much and just use it. In fact you can take the larger plug( 1/4" ) and put it straight into the radios headphone jack and thats always worked just fine. yeah the impedance is different, yeah you won't get optimal power transfer, but its always worked plenty well enough for me. The microphone is the part you should pay attention to. Especially the type and levels between what the radio expects and what the headset is providing. Understanding the circuitry in that magic black box might be necessary.

Good luck and enjoy the project to tinker on.

 

[AK9R]

At least one guy has taken this whole interconnecting radios with headsets things to an extreme: Open Headset Interconnect Standard

 

[serial14]

@AK9R interesting link, I'll have to go over that.

At first glance, it reminds me of this XKCD Standards

 

[guttapercha]

You're welcome.

If you have "the whole setup", it might be worth just "double checking" that it all still works. Then you have a base line for your expectations. You can also try operating with the headset to see if you really like it. In the aviation world, there are two types of people... people that like DCs and people that don't.

I'll offer a couple observations on utilizing DC headsets... especially how it applies to ham radio. Again to help set your expectations

• DCs have a lot of passive noise attenuation. You can look at the specs but its something like 26-32dB of outside noise attenuation. This is very helpful in things like noisy airplanes, vehicles, etc. This can also be great for radio if you're operating in an area with ambient noise that you'd rather not hear. It comes at a price, people can sneak up on you easier
• DCs have alot of clamping force. This is one of the main gripes from people that don't like DCs. DC offers various ear cups to help with comfort. My personal favorite is the gel ones. For extra comfort they sell cotton things that go over them as well.
• The human mind is used to hearing your self talk. When you're wearing DCs you're ears can't hear your mouth talking as well. As a result you really have to be careful that you don't start yelling. With awareness and practice its possible to re-train your brain to overcome this and just talk normal.
  • This is probably this biggest factor in "usability" with the ham radio world I'd guess.
• To account for the above, systems that use DCs have a feature called "side tone" that puts some of the mic signal back into your headphones so that you can hear your self. On all the stock ham radios I've used headsets with, I haven't found one with side tone by the way.

Finally some commentary on your findings about impedance. You are absolutely right, aviation does it differently than ham radio. I don't know why. But I will say I haven't worried about the headphone impedance value much and just use it. In fact you can take the larger plug( 1/4" ) and put it straight into the radios headphone jack and thats always worked just fine. yeah the impedance is different, yeah you won't get optimal power transfer, but its always worked plenty well enough for me. The microphone is the part you should pay attention to. Especially the type and levels between what the radio expects and what the headset is providing. Understanding the circuitry in that magic black box might be necessary.

Good luck and enjoy the project to tinker on.

Solid info! Thanks. You are right - I might not even like using it! I've worn one a few times flying GA with pilot friends, and I sure wasn't thinking about the particulars of the headset in those instances (rather, I was marveling at going up in a tiny plane!). The CB world has something called "talkback," which sounds like the same thing as sidetone, but I've never seen such a feature on a ham rig other than for hearing CW.

Thank you so much for your thoughts on all of this,

Josh

 

[guttapercha]

@AK9R interesting link, I'll have to go over that.

At first glance, it reminds me of this XKCD Standards

I love when people get OCD about this kind of stuff and want to share it with the world. Very cool. Thanks!

 

[AK9R]

The CB world has something called "talkback," which sounds like the same thing as sidetone, but I've never seen such a feature on a ham rig other than for hearing CW.

Icom HF radios have a feature called "Monitor". Is that what you are talking about?
(from the IC-7300 operators manual)

 

[AI7PM]

I'd like to do this with a Plantronics MS50.

 

[guttapercha]

Icom HF radios have a feature called "Monitor". Is that what you are talking about?
(from the IC-7300 operators manual)
View attachment 142980

Thanks - I will check this out!

 

[krokus]

At least one guy has taken this whole interconnecting radios with headsets things to an extreme: Open Headset Interconnect Standard

For those unaware, Smitty is a regular part of the Ham Radio Workbench podcast, and talks about his efforts on the headset interface.

Ham Radio Workbench Podcast Episodes

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www.hamradioworkbench.com