I will only comment on the part reproduced below - audio return is NOT audio ground. In the case of the Motorola amp cited, I suspect the audio amp output is a bridged amplifier, and for those, neither speaker lead should be grounded (it shorts half of the audio amplifier.
BUT, Jim Brown was talking about unbalanced audio inputs, not speaker outputs. In the ham world and the world of consumer audio, most audio inputs are unbalanced, with one conductor (the shield) connected to "ground". That ground used to be the equipment enclosure, but more recent implementations circumvent that and put the connection to the shield onto the PC board rather than the enclosure - and often the enclosure is plastic which creates yet another set of potential problems. We used to connect our audio (and RF) jacks directly to the enclosure and then inside the enclosure, we would route that connection to the circuit contained in that enclosure - no "pin 1" problems because the shield of connected cables were connected first to the outside of the enclosure.. In today's implementations, pin 1 problems abound because jacks for any and every purpose are designed to connect to the PC board and may or may not have any connection to the equipment enclosure. That allows noise and other undesired signals to be introduced onto the device circuit board without being first stripped off by the (grounded) metallic enclosure for the device in question. We have come a long way in convenience for manufacturers, but several problems have occurred along the way, and they are not easy to correct. 73, Don W3FPR On 11/1/2011 9:58 PM, Rick Bates wrote: > In the case of Motorola radios, you'd have to ask them why, but never assume > that either side of a speaker (for example) is chassis grounded, or you'll > blow up a very expensive audio amp (like on the popular GM300). A careful > resistance test should be done before connecting audio ground to chassis. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
