Please comment on this grounding scheme. - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th August 2011, 04:40 AM   #1
diyAudio Member
 
Join Date: Dec 2008
Location: Victoria, BC
Default Please comment on this grounding scheme.

I came across this advice 'on the internet', and it was something I had not seen previously.
Quote:
Since you're using a three-wire plug, how are the other two wires connected? The white wire in the AC cord is supposed to be neutral, and black is the hot. The white wire should connect to circuit's ground. The green ground wire should go to the chassis. A 47k resistor and a MOV would connect circuit ground to chassis. Might be easiest to simply disconnect the green wire as suggested and make sure the circuit's "ground" side goes to the white wire.
End quote

I'd appreciate comments from knowledgeable builders.
Thanks.
  Reply With Quote
Old 4th August 2011, 04:51 AM   #2
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
NO!

The only thing that should be (firmly) connected to the chassis is the GREEN earth ground wire.
It can then connect to your circuit ground,in whichever method you like (directly,or through a resistor/ground loop breaker,etc.)

Neutral should NEVER connect to anything other than the 'primary' side of your power transformer,and any associated switch,etc. that may be located there.
It should NOT be connected to your circuit ground or anything other part of your circuit.

This way the chassis is 'firmly' earth grounded,in case anything should malfunction. And,the power transformer provides galvanic/magnetic isolation from the mains for your circuit to use.

Again,no part of the mains wiring should be connected to the chassis/circuit -EXCEPT- the Green Earth Ground.


EDIT: A second thought, Is this pertaining to Line-Operated circuits? !ALWAYS! use an isolation transformer with those type of circuits!

Last edited by DigitalJunkie; 4th August 2011 at 04:53 AM.
  Reply With Quote
Old 4th August 2011, 05:25 AM   #3
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
I second what Digital Junkie says. No part of the AC line should connect to the chassis. In a perfect world the white wire could be relied on as being neutral if everyone did their job correctly. But this is not always the case. And this is the reason that neither side of the line should be grounded.

The purpose of an MOV is to protect instruments from over voltage. If used, they should be connected across the AC line after the unit's local fuse. Should the AC line go too high, the MOV will conduct heavily (short out) and blow the fuse. It should not be used to connect the mains or circuit to ground in any way.

If you have a third "green" wire connected to chassis ground, do not remove it! It's there for safety reasons.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 4th August 2011, 05:49 AM   #4
diyAudio Member
 
Join Date: Dec 2008
Location: Victoria, BC
Thanks for the comments, guys. That's what I think as well, but just needed a 'reality check'. I really don't like to see stuff like that hangin' out on the 'net where some beginner might take it seriously.

Quote:
Originally Posted by DigitalJunkie View Post
Neutral should NEVER connect to anything other than the 'primary' side of your power transformer,and any associated switch,etc. that may be located there.
And then, only if you are switching the neutral and line with a DPST switch. The switch and fuse should both be in the line ('hot') side- not like those hundreds of thousands of old Fenders with the switch in one side, fuse in the other. Of course, with them it didn't matter, since the 2-prong plug wasn't polarized- so the wiring was always 'half-right'. You see that style copied in a lot of amateur-built guitar amps with 3-wire plugs, still.
  Reply With Quote
Old 4th August 2011, 06:01 AM   #5
diyAudio Member
 
Join Date: Nov 2009
Location: Los Angeles
It's not supposed to happen but sometimes the hot and neutral get swapped in the house wiring. NEVER assume the neutral is in fact neutral. If you build gear that requires the neutral in fact be neutral, it is a foolish design.

G
  Reply With Quote
Old 4th August 2011, 06:44 AM   #6
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
Quote:
And then, only if you are switching the neutral and line with a DPST switch. The switch and fuse should both be in the line ('hot') side- not like those hundreds of thousands of old Fenders.......
Exactly correct!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Grounding scheme Rassmussen Tubes / Valves 5 24th June 2010 02:13 PM
Grounding scheme Sandor Construction Tips 12 9th June 2010 09:59 PM
grounding scheme Leolabs Solid State 2 12th September 2006 02:43 PM
Grounding scheme MWP Chip Amps 14 29th June 2004 10:21 PM


New To Site? Need Help?

All times are GMT. The time now is 02:13 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2