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Old 17th January 2010, 01:25 PM   #1
wwenze is offline wwenze  Singapore
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Join Date: Mar 2008
Default Why doesn't it short? Or am I missing something?

Funny I only thought of this now... (as opposed to before mounting the binding posts of the amplifier)

When mounting a connector onto the chassis a hole just slightly bigger than the diameter of the screw thread is drilled. Then the nut is turned to tighten the connect in place, with a plastic washer (or "thingie" in the case of binding posts) insulating the nut(s) from the chassis. This seems pretty standard.

But, since the space at the hole between the thread and the chassis is so small, shouldn't there be a high chance of the thread touching the chassis hence forming a short to ground?

Yet, when troubleshooting an amp and thought of this problem, I went to check whether there is such a short. Strangely none of the 6 connectors were connected to ground. Heck, if they didn't provide an insulator with the package it should be safe. But why is it safe to do so?

Last edited by wwenze; 17th January 2010 at 01:35 PM.
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Old 17th January 2010, 03:24 PM   #2
wwenze is offline wwenze  Singapore
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Join Date: Mar 2008
Or is it that the bottom of the washers (or the washer-like thingie for binding posts) are not flat on at least one side so that when mounted properly with a hole drilled according to datasheet the washer partially enters the hole and insulates the connector from the circumference of the hole? If so that's pretty creative.

Click the image to open in full size.

Pic taken from datasheet of the Neutrik RCA that I'm using, washers colored red. I clearly remember other binding posts' washers having this bump at the bottom also, fatter though.

Better check the speaker terminals when I get back next weekend
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Old 17th January 2010, 07:08 PM   #3
mjf is offline mjf  Austria
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hello.
yes,the inner ring isolates the plugs from the case.
picture shows a banana connection.
greetings
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Old 21st January 2010, 11:42 PM   #4
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Thanks for this thread. I was wondering the same thing about the Neutrik RCA plugs on the amp I'm building. The ESP P101 amp instructions stress that RCA ground <> chassis ground. I don't think my hole is going to be the right size because I didn't have a metric drill set, I had to use the closest standard equivalent.
Not sure if I will try to widen the hole...I was also thinking of wrapping teflon pipe tape around the part of the connector that would contact the chassis. And of course testing for continuity with my cheap Radioshack meter.
Not that I didn't know this, but aluminum is so soft it's kind of funny to work with. When I was drilling holes for the XLR's M3 screws I held them in place with one of those rectangle-shaped Vise grips. ($16 at Lowes but a good investment for a project of this nature) The shell of the XLR pressed so hard against the aluminum that the very tiny word Liechtenstein was pressed, backwards of course, into the Al. It's ever visible after painting with black appliance "epoxy".
This thread reminds me that, when I joined diyaudio I was going to propose that there should be a "noobs" forum for people like me...but decided against suggesting it because there might be a good reason for it not already being here. Perhaps nobody with experience would actually read it haha. But seriously, to someone new to project construction there are just scads of little pesky questions that are a major preoccupation to figure out. I've solved a lot of them on my own but it took a lot of time. For example one of the ones that's still an albatross: what the heck does a snap-in capacitor snap into? I bought a copper bus bar, which ESP suggests for grounding, because I was going to order some copper sheeting for an outdoor project anyhow. I suppose I can drill a 1/16" inch hole and coerce the snap-in terminal into it, but based on their design it does look like there's something of a particular shape they are supposed to mate with...? What though? Google search of "snap-in capacitor terminals" or searches on the mouser site didn't find anything. The caps I'm using are the Panasonic 10k uf ones that diycable had on sale. Hope they are up to the task...
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Old 22nd January 2010, 12:33 AM   #5
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Location: Wirral UK
Hi snellwilco.

Have a read here Electronics/Capacitors - Wikibooks, collection of open-content textbooks

The term snap in applies to snapping into a pcb and holding its own weight prior to soldering. As opposed to radial leaded caps that fall out as soon as the board is inverted. They also fall directly into the bin or roll under the heaviest item of furniture to a point which is just out of reach, no matter which angle you reach from.

There is a thread going on about case fabrication here Build your own case A small pillar drill is well worth having if you are going the diy route.

Hope it helps.

John
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Old 22nd January 2010, 08:41 AM   #6
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Default thanks

Yeah, that not too far off from what I'd figured, which is that there once might have been some special mounting post for them (I was thinking it would look like a ceramic tube socket, or maybe more like a fluorescent light socket) but that nobody used them anymore and just straightened the pins, inserted them into a PCB, and then bent them back slightly. I knew it was a stupid question which is why I only wanted to ask it in a forum for newbies hahaha.
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Old 22nd January 2010, 03:33 PM   #7
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Hi snellwilco.

We've all got to start somewhere. Some were born with a soldering iron and calculator in hand, for the rest of us it can be a steep learning curve.

I'm only a few chipamps in front of you. One thing I think could be good for beginners would be a list of meanings for some of the abbreviations used, I/V, VAS, VBE, Q etc.

John
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Old 23rd January 2010, 04:26 AM   #8
wwenze is offline wwenze  Singapore
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Went to check after I got home yesterday, the RCAs are alright because I drilled then according to what the datasheet says, but for the binding posts the inner ring is as thick (or as thin?) as that of the RCA it'd escaped my attention. As I was too used to drilling wood and plastic I drilled holes the size of the screw instead of the inner ring. So it was due to pure luck nothing blew up.

You'd think there should be more warning on this for beginners. I'm lazy to drill bigger holes at this stage so tape does the job.
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