[GSMacLean]

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Goldwings 4 ever wrote:

You certainly should be able to. Earth is earth or as we say over here "ground is ground".:cooldevil:

Not necessarily! If the microphone input is using a floating ground, or, more likely, if the headset output uses a +/- voltage supply, so that the "-" on the headset is not actually ground, then connecting the two together could not work at the least, and do damage at worst.

In the case of the GL1100 intercom, the headset ground and the microphone ground ARE connected together. I don't know for sure about the 1500.

My suggestion would be to turn everything off, and use an ohmmeter to measure between the headset ground and microphone ground. If you have anything more than an ohm or two resistance between the two, then chances are that they are not sharing a common ground, and I wouldn't do what you're planning. If you see no resistance, or less than a couple ohms, then you should be OK.

 

[GSMacLean]

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It sounds then like the mic ground may be floating (not uncommon). I know for a fact on the GL1100 (Type II) they are shared grounds, but it sounds from your reports here that on 1200 on upwards, they are not.