Multiple XTL's one speaker

[c17lvfd]

Good Afternoon All,

Ive searched several areas without success in finding a answer. If this has been answered my apologizes.

Im building a radio rack (a Syntor x9000 and 3 xtl5000's)... I am making a audio panel to run the setup via 1 handheld mic and a single speaker. It's a very similar setup to what I had setup in my air-medical helicopter except we used xts5000's. I've got all the mic pinout a setup and working.

My question is to the audio. Ill have one external speaker and a output for a David Clark headset. I know you can't ground Motorola radios audio feed because it will blow the audio circuit. My question is can I tie all the (-) leads together to the speaker (-)? In addition do I need to put anything on the individual positive leads such as a resistor or diode to prevent back feeding into the other radios.

Any insight is greatly appreciated!

Thank You,
Seth

 

[Alpha]

If anything, you'd want a cap to isolate the DC ground from the audio (-) lead. That will allow the AC audio to pass to ground normally, but blocks the +12V DC on the speaker leads. You probably want to use caps on the (+) leads too, to keep them from affecting one another. Ultimately, a 1:1 8-16 ohm matching transformer would be best, it will not cause "thumps" as the DC level switching through a cap can have, and will completely isolate any DC component. Then, you can tie both leads of all the transformers together (one side to ground, one to a "hot" common) to mix the audio.

You might also consider a selector switch on the hot sides, then you would route all the (-) leads through a cap or transformer to ground, and send the hots to a rotary selector switch or something like that.

 

[com501]

Isolation transformers would be the way to go, for all the radios, including the X9000, as you are dealing with not only the DC potential but an AC component of the received audio which can be several volts depending on volume setting of each radio. You WILL need a speaker capable of handling many watts of audio, the XTLs and X9000 are capable of more than 10watts each at full volume. Your iso transformer will need to handle the same power for each radio, also, or smoke will result.

For my two vehicles, I just found clever places to hide speakers and for my headset mix I just used a low level fixed-volume tap off instead.

 

[c17lvfd]

Thank you both for the information and input. This gives me a great starting point.

Seth