Voltage between chassis ground and earth ground - Page 2 - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 15th November 2012, 10:58 PM   #11
diyAudio Member
 
Join Date: Jun 2011
I would recommend a new power transformer. sometimes those old power transformers don't have the greatest isolation. and remember, when you plug your guitar amp in, you are holding onto the amp's ground.


Its better to error on the side of caution. there has been many musicians that died from electrocution this way.

and to add I would recommend taking it to someone like a tv repair man to test the leakage current just to be on the safe side.

Last edited by DavesNotHere; 15th November 2012 at 11:00 PM.
  Reply With Quote
Old 15th November 2012, 11:03 PM   #12
diyAudio Member
 
Triodethom's Avatar
 
Join Date: Dec 2009
Location: Newnan GA
Quote:
Originally Posted by indianajo View Post
Hammond organ had a standard for earth connecting old chassis. 10k resistor connected between organ amp or preamp and "known earth ground". That known earth ground is the new 3rd wire of your power plug, if the wall plug is wired correctly. Measure voltage across the resistor with a AC VOM with more than 5 kohms / volt. (The cheapest RS meter is this high, typically). More than 4 VAC, the organ has to have the power transformer replaced. Before the earth ground is installed. To prevent insulation breakdown of the transformer (ie fire).
Not assured that the power transformer is the cause in the case of your amp, but cotton insulated wire could be the problem.
So off the top of my head thats like .4ma and this one is 50ma a factor of 200 high . Given that the main transformer is in need of replacement unless there is a resistor not on the schematic from the ht to chassis leaking the 50 ma which is like 2.5 watts at 50 volts ( 50 volts at 50ma ) there should be some amount of heat or some thing should be warm I would think. Reverse the polarity on the ac plug and measure voltage as you did be fore and please report back . so it 50 volt one way what is it the other ?

Last edited by Triodethom; 15th November 2012 at 11:08 PM.
  Reply With Quote
Old 16th November 2012, 08:53 PM   #13
diyAudio Member
 
Join Date: Nov 2010
Thank you all for your guidance. I will spend a sometime this weekend testing this thing as well as changing a capacitor or two.

Regarding "2.5 watts at 50 volts (50 volts at 50ma )"; note that I did not measure these at the same time. I measured the static voltage (essentially no current) at 50 V and 50 ma current through the multimeter () (essentially a ground wire with little/no voltage difference). I think maybe I am chasing ghosts with these measurements and that the voltage accross a 10k resistor will be much more instructive.

I still think something is wrong. Hopefully it is not the power transformer, but with my luck it is always the most expensive component.

For what it is worth, the amp does sound great except for a crackly issues at high volume. I will go through my modifications and problems in more detail after I get this safety issue figured out.

I appreciate all your help.
  Reply With Quote
Old 16th November 2012, 10:23 PM   #14
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
If you are measuring 50mA leakage then there is a serious fault and a serious safety issue. Be very careful.
  Reply With Quote
Old 17th November 2012, 08:20 PM   #15
diyAudio Member
 
Triodethom's Avatar
 
Join Date: Dec 2009
Location: Newnan GA
Replacing the main transformer with one from Edcor ot hammond is in order I think.
  Reply With Quote
Old 17th November 2012, 09:39 PM   #16
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Gotta say everyone who is suggesting you replace that power transformer is giving you the best possible advice!

As has been pointed out 50mA of leakage current is extremely high, the allowable limit on a metallic enclosure is something on the order of 0.1mA and with a single fault 0.5mA - remember this is going to be a guitar amplifier and you will be well coupled to it when playing a guitar, all of that leakage current will travel through you to any grounded object (like a mic.) or vice versa..

Grounding is insufficient in this case as you cannot count on a reliable ground under all circumstances so a good power transformer will provide you protection under those circumstances.

Using a GFI or two to provide power and ground fault protection while gigging is not a bad idea - will provide protection against dangerous leakage currents flowing through various devices being handled during a performance.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 17th November 2012, 09:42 PM   #17
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
And since this is a guitar amp I'm going to move this to Instruments & Amplifiers per forum policy.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 19th November 2012, 04:21 AM   #18
diyAudio Member
 
Join Date: Oct 2004
Location: Adelaide South Oz
Guys,
Recent advice on leakage current limits from a reputable source.
Leakage Current Limits for Electronic Equipment Used in Non-Patient-Care Areas

THe 50mA (50,000 micro amps) you measured means that the amp in its current state would be condemned as UNSAFE by any testing authority. Do NOT use until fixed.

Cheers,
Ian
  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
Chassis, ground, earth: connect? starbase218 Solid State 3 14th November 2007 08:56 AM
chassis ground vs. earth ground avid Chip Amps 4 10th November 2006 12:56 PM
first I earth the chassis for safety but why do I need to conect it to my ground... frank2395 Pass Labs 4 20th May 2005 12:15 PM
signal ground and earth ground ttray321 Tubes / Valves 9 3rd May 2005 03:14 AM
Chassis Ground = Circuit Ground --> Problems? rhildenbrand Pass Labs 5 23rd April 2004 01:08 AM


New To Site? Need Help?

All times are GMT. The time now is 03:32 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