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Post by jin167 on Mar 17, 2018 8:28:17 GMT -6
www.theabsolutesound.com/articles/tip-of-the-month-ac-polarity/I don't understand the point of the proposed exercise.. sounds like a nut job to me within my boundary of knowledge in electrical engineering but then again there could be a good explanation. Can anyone think of a technical explanation for this? It looks like this is a well-known trick among the hifi crowd but I don't hear this being discussed in pro forum (possibly for a good reason).
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Post by johneppstein on Mar 19, 2018 11:40:27 GMT -6
www.theabsolutesound.com/articles/tip-of-the-month-ac-polarity/I don't understand the point of the proposed exercise.. sounds like a nut job to me within my boundary of knowledge in electrical engineering but then again there could be a good explanation. Can anyone think of a technical explanation for this? It looks like this is a well-known trick among the hifi crowd but I don't hear this being discussed in pro forum (possibly for a good reason). I only got a couple paragraphs in before I had to stop reading - the "advice" offered in this article is both stupid and dangerous.. you DO NOT want to defeat the polarity in you AC wiring, for the simple reason that one side is HOT and one side in NEUTRAL, which is bonded to ground in the power box. If you swap hot and neuitral you have a very real possibility of a (possibly fatal) ground fault should something go wrong in your groundf wiring, which is fairly rare but DOES happen. You have to understand the way US residential power systems work - they are nominally 120 VAC unbalanced, split from 240 VAC balanced. That's right, what comes into your house is 240 VAC with a center "neutral" wire that forms a return. Theoretically the neutral should not be carrying any serious current, as the load should b e more or less balanced between the two hots, which are in reverse polarity to each other. In practice the two legs seldom balance perfectly, so there is some current flowing in the neutral. The ground is just a safety ground and should not be carrying anything. The upshot is that if you have any sense you don't want to be swapping hot and neutral into your gear because if the ground gets compromised you have a dangerous situation. Ground loops CAN be a problem with some gear, but the rinkydink amateur fix given in the article is NOT the solution and does not address the actual problem, which is poorly designd internal grounding from some manufacturers, including some that really should know better. For an in depth explanation of the problem and its solution I recommend you to the AES White Papers written by Mr. Bill Whitlock, former head honcho at Jensen Transformer, now retired. The papers are available for free from Jensen. You can also start with this: www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwiHvMeq-vjZAhVQ7WMKHZU2DEYQFgg8MAM&url=https%3A%2F%2Fcentralindianaaes.files.wordpress.com%2F2012%2F09%2Findy-aes-2012-seminar-w-notes-v1-0.pdf&usg=AOvVaw1WOleohPfiVFfR0tfkLQirI'm very disappointed in Absolute Sound for publishing this - usually they're not all that bad as audiophile publications go. |
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Post by svart on Mar 19, 2018 11:54:13 GMT -6
Yeeeeah...
If the device has a transformer, it does not matter which way "current flows". Most of the time, the primary of the transformer is the innermost coil, which will see equal parasitics looking from either of the primary line input conductors.
These should be inherently isolated from ground in the unit anyway.
This is another case of "wishful thinking" as a lot of "well-known tricks" have always been.
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Post by EmRR on Mar 19, 2018 12:12:43 GMT -6
This is like a buildout of a misunderstanding of the old style Fender ground switch.
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Post by johneppstein on Mar 19, 2018 21:32:07 GMT -6
This is like a buildout of a misunderstanding of the old style Fender ground switch. And of course nobody ever got shocked by that! |
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Post by donr on Mar 19, 2018 22:26:58 GMT -6
AC polarity story Back in the day when everybody was on guitar leads instead of wireless, there was often ground potential between guitar strings and mics onstage. Sometimes it was barely tolerable, electric shocks on the lips singing while touching the guitar, even with foam wind screens on the mics. In our band, we used to do a live gag where we'd cross guitars and do a stereo noise segment in the middle of a song, originally a cover of Steppenwolf's "Born To Be Wild." When we started out, it was our set closer, 'cause we didn't have a hit of our own yet. At one time, Gibson made a tune-o-matic bridge with nylon saddles. My bandmade Eric Bloom had a gold top Les Paul with those saddles, and one night when we crossed guitars, (our guitars [both Gibsons] which were grounded through the tailpieces) visual sparks flew off the strings and after, we discovered the strings on his guitar had melted into the bridge saddles. Yikes, that level of ground potential difference never happened again.  Although if we COULD have made it happen on demand, we'd have dealt with the danger of electrocution for the stage drama of the sparks. |
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Post by johneppstein on Mar 20, 2018 11:15:08 GMT -6
AC polarity story Back in the day when everybody was on guitar leads instead of wireless, there was often ground potential between guitar strings and mics onstage. Sometimes it was barely tolerable, electric shocks on the lips singing while touching the guitar, even with foam wind screens on the mics. In our band, we used to do a live gag where we'd cross guitars and do a stereo noise segment in the middle of a song, originally a cover of Steppenwolf's "Born To Be Wild." When we started out, it was our set closer, 'cause we didn't have a hit of our own yet. At one time, Gibson made a tune-o-matic bridge with nylon saddles. My bandmade Eric Bloom had a gold top Les Paul with those saddles, and one night when we crossed guitars, (our guitars [both Gibsons] which were grounded through the tailpieces) visual sparks flew off the strings and after, we discovered the strings on his guitar had melted into the bridge saddles. Yikes, that level of ground potential difference never happened again. Although if we COULD have made it happen on demand, we'd have dealt with the danger of electrocution for the stage drama of the sparks. I remember that routine - Eric used to ride his bike out on stage! Don't remember any sparks, though.... Your crew wasn't doing proper ground checks - always touch the strings od the guitars to the microphones (assuming everything is wired) - if there's a problem you'll hear the crackle! |
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Post by matt on Mar 20, 2018 11:19:14 GMT -6
Although if we COULD have made it happen on demand, we'd have dealt with the danger of electrocution for the stage drama of the sparks. Now THAT'S Rock 'n' Roll! |
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Post by donr on Mar 20, 2018 11:54:35 GMT -6
AC polarity story Back in the day when everybody was on guitar leads instead of wireless, there was often ground potential between guitar strings and mics onstage. Sometimes it was barely tolerable, electric shocks on the lips singing while touching the guitar, even with foam wind screens on the mics. In our band, we used to do a live gag where we'd cross guitars and do a stereo noise segment in the middle of a song, originally a cover of Steppenwolf's "Born To Be Wild." When we started out, it was our set closer, 'cause we didn't have a hit of our own yet. At one time, Gibson made a tune-o-matic bridge with nylon saddles. My bandmade Eric Bloom had a gold top Les Paul with those saddles, and one night when we crossed guitars, (our guitars [both Gibsons] which were grounded through the tailpieces) visual sparks flew off the strings and after, we discovered the strings on his guitar had melted into the bridge saddles. Yikes, that level of ground potential difference never happened again. Although if we COULD have made it happen on demand, we'd have dealt with the danger of electrocution for the stage drama of the sparks. I remember that routine - Eric used to ride his bike out on stage! Don't remember any sparks, though.... Your crew wasn't doing proper ground checks - always touch the strings od the guitars to the microphones (assuming everything is wired) - if there's a problem you'll hear the crackle! Yeah, we'd do it ourselves to know if there was going to be a problem. Some nights, the ground problem could not be resolved. Different power for the PA, the stage etc. One night we played outdoors at Jones Beach NY in the rain. I had to put plastic bags over my feet because I was getting shocks through my shoes and the wet stage. |
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Post by johneppstein on Mar 20, 2018 21:31:32 GMT -6
I remember that routine - Eric used to ride his bike out on stage! Don't remember any sparks, though.... Your crew wasn't doing proper ground checks - always touch the strings od the guitars to the microphones (assuming everything is wired) - if there's a problem you'll hear the crackle! Yeah, we'd do it ourselves to know if there was going to be a problem. Some nights, the ground problem could not be resolved. Different power for the PA, the stage etc. One night we played outdoors at Jones Beach NY in the rain. I had to put plastic bags over my feet because I was getting shocks through my shoes and the wet stage. I generally have any leather soles replaced with Neolite (rubber). Leather conducts. Hoo-BOY does leather conduct! I learned that one early playing with my garage bands on the concrete floor (which also conducts) of my parents' garage in high school. I used to pull the rubber floor mats out of the car to stand on! My first ever gig I went up to the mic to sing backup on The Animals' "I'm Cryin'" and got a BIG FAT SPARK right up my front tooth! Actually knocked me out for a second, although I came to before hitting the ground.... (Of course that's nothing compared to tying into the filter caps in a Marshall Major that I forgot to discharge.....) |
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Post by jimwilliams on Mar 23, 2018 13:59:18 GMT -6
The AC polarity does affect noise fields some non-grounded gear. One of my bench headphone amps had a non-grounded AC cable. It generated a nice hum field my scope probes easily pick up if anywhere near by. Switch to a grounded AC cable with proper chassis grounds and that all goes away.
I hate The Absolute Sound mag. They sent me a comp scrip and I keep buying stuff. Emotiva speakers, Schiit boxes, Pro-Ject DAC's, etc. Not everything in there costs $25,000.
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