OK....
I will try to post a picture of the completed circuit later if needed.
These components were not available at Radio Shack, Found them at an electronics supply store. I have ordered a small plastic project box about 1" X1.5"X.75" to house the circuit and it will be attached with velcro to the Zumo mount.
Before building this circuit read the last paragraph for a much better design.
I enlisted the help of a Telecommunications Tech, with design of a proper circuit. Greg found that a 1meg Potentiometer (pot) was necessary and a 1ufd electrolytic capacitor (cap) using shielded audio cables to keep out any stray electrical noise. The cable needs a 2.5mm female connector/socket on the Starcom1 Advance end and a male 2.5mm plug on the GPS end. A pot is needed to properly adjust the audio output level of the Starcom1 to each persons voice/helmet because every voice is different and where the mic is located in the helmet in relationship to their lips.
When building the circuit using a shielded audio cable as above, cut and connect the center conductor from the Starcom1 side and the negative side of the cap to the center conductor of the pot and connect the GPS side of the cable center conductor and the positive side of the cap to one of the other legs of the pot. Remove insulation from the other conductor and attach it to the remaining unused leg of the pot cable. Remove the mic plug from the GPS and plug it into the female connector of the made up circuit and the male end into the GPS, adjust the pot to mid range and test the phone by turning the pot to get the best results for you voice, mic and phone. I used a phone answering machine to record various settings of the pot with its position noted to adjust the pot correctly.
To better undestand my testing I'm 5' 9" with a 29" inseam. After adjusting the pot where it sounded best I rode the bike making calls to test it. No one knew I was riding my bike while calling them until I told them I was. At 60 mph with Cee Bailey (CB) Ultra tour fully down, my face shield open on my full face helmet no one could hear wind noise, with the CB shield up at 80 mph it was as clear as when I was sitting still and also on my answering machine.
Grant
After more research the circuit has been changed and it now has much better response volume wise, operating as it should have from the factory. The change is using the same components cut shielded audio cable as above, connect the center conductor from the Starcom1 side to one side of the pot and the negative side of the cap to the center conductor of the pot and connect the GPS side of the cable center conductor to the other outside pot connector with the positive side of the cap to the same leg of the pot. DO NOT attach the second conductor of the shielded cable to the pot.
