Why do the Garmin GPS units require a special cable?
Garmin GPS units use a bridged amplifier output. Most devices use singled ended amplifiers, which means one conductor is ground, the other(s) provide the actual signal. In a bridged amplifier, there is no ground reference, both pins provide signal. Should a bridged amp be connected to a singled ended input, one pin will be grounded and will prevent the amplifier from working properly. The special cable (PC-GPS) isolates the grounds between the GPS and the Mix-It but allows the AC signal to pass through to the Mix-It’s circuits, allowing you to hear the GPS normally.
Earlier Garmin GPS units (mono ouputs, typically those without MP3 or satellite radio capability) use an ungrounded amplifier output. Other products require a special isolation cable, the Mix-It2 does not. The GPS just needs the proper cable to plug into an isolated input on the Mix-It2 (either a PC-GPS2 for 2610/2620 models). Later models (28xx, Zumo, Nuvi, etc) with stereo jacks can be plugged into a stereo input on the Mix-It2.
