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Audio Amp ground.. which one?

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That sounds fine, I think you were getting confused by us techs babbling.
You can connect an rca jack to jack with ground thats fine, nearly every stereo does.
In some circumstances it might be better to use different grounding methods, if your system works as its connected up then use it that way.
It seems that your amp blew up because there was a cable fault, ie broken.
My opinion on home audio violating the grounding at one end rule is that not everyone connecting up a stereo is not an electronics technician, if I were to connect up mine with seperate grounds and loads of jazz then I'm sure something would end up in smoke.

You are ever so correct in wanting separate grounds. When we did our 100 Watt amplifier for the AirCraft Carrier announcing system (2500 Watts total system), 100W amp chips were available, but not in mil spec, so we had to do it the old fashioned way. Our audio design engineer wanted each circuit on the board to have it's ground come back to a single point connection with ALL of the other circuit grounds on the board. Of course, with limited space available, this was not practical, so we had to work out a compromise that worked. Basically, the most sensitive stuff goes on the end of the ground, with the heavier current circuits located closer to the main ground point.

Having done circuit board design for over 20 years now, a ground plane is best, but when you're only doing a 2 layer board, you may not be able to dedicate one layer to a ground, so a ground grid is your next bet. You want as many ground to ground connections as possible. This does not violate your shielding rules, as this is not a shield.

You are correct when you say shields should be connected at one point only, and yes, it is usually at the source but this is not always the case or fesible. In 1987 I built a digital tachometer (Digitach®). I used a divide by n counter (makes incoming clock a two rpm period) and a LUT (look up table), without using a micro as they were fairly expensive at the time. My buddy put it in his car, and I asked him how it was working, and he said, "Lously". So I got in his car and looked at it. It was all over the place (it had a digital display and a bar graph, it read 4 bytes from the clock count, so it had 3 digits = 12 bits and 20 bits for bar graph info). I asked him, "did you ground the shield?" "Yes" "which end" "both ends"... "oh," I said, and cut the shield from ground on the board, and it fell right into place, working perfectly...

There is a book I read in the 80's, "Grounding and Shielding Techniques for Instrumentation", author unknown as the book has disappeared from my library (just googled - Ralph Morrison). I only read through it once and in 2002 was able to troubleshoot a ground loop problem in a video cockpit display system over the phone (I built the power supply/video amp board for Flight Systems Inc out of Florida) and they swore my pcb was 'noisy', but I had determined it was their system wiring and was correct.
 
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During my time as a sound engineer I came accross a few ground issues, and every time it gave me a sinking feeling, some wers sorted easily and some were very difficult, the problem when your dealing with musicians and roadies it that you cant just disconnect a ground at the sending end, as you just know they'll plug that lead into something else the next day and blow something up, just like what ahppened with the o/p when his ground was disconnected.
 
yes, dr, I feel your pain. As a design engineer, when I design a board, especially if the system will be wired by electricains, I have to make it "idiot proof". My last design was a PTAT temperature sensor (current proportional to absolute temperature) to 4-20mA output board, and I designed the sensor input to be mistakenly connected to +24V or ground, which my client thanked me for. It's just something you need to be aware of. I just troubleshot a hot tub for a friend, and decided the GFI was wired incorrectly. The electrician swore up and down that I didn't know what I was talking about, until I showed him his mistake. The GFI wouldn't pass the current to run a light bulb, let alone a hot tub. He had mixed up the two neutrals.
 
I have gone down in the world from a design engineer to a lowly electrician on plant equipment.
In defence to folks like us when your in a crappy environment, dont have the right equipment and receiving pressure from above mistakes liek that happen, for 2 reasons, one pressure and also the desire to give a you know what, the latter hasnt got to me yet, but I see it all the time.
 
don't be so down on yourself, dr, we all do what we must do... I took a job last year as a test technician, not because I wanted to, but because it paid the bills (I made $73K, but had to work 500 hours overtime to get there).
I'm not dogging electricians per se, but everybody makes mistakes (even me, believe it or not). It's just that when one wiring error blows up a $500 board, people get a little irate (some even go after the designer). Since I've worked on both ends, I try to make my stuff as bullet proof as possible.
 
I'm not so much down I have a job thats little hassle reasonably well paid and 5 mins down the road, thats why I'm here.
My lethargy was more aimed at it shouldnt be more difficult dealing with people you work with/for when you are higher up the ladder, but that does seem to be the case here in the uk.
 
Try disconnecting the ground to the sub, and connect a 100 ohm resistor in line with the ground, that will lift the ground at whatever end needs to be lifted.

Another way would be to connect a beefy cable from the ground on the sub to the ground on whatever feeds the sub signal wise.

Theres quite a lot of distortion on the vid, maybe the cam couldnt cope with the lf, either that or sounded like possibly excursion distortion.

the sub was playing that's not distortion.. sticking the camera right in the port tube will have that effect, I will have to do a video tomorrow of it with no sounds playing.
 
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