Definitive earthing advice sought. - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 13th September 2006, 07:28 PM   #1
hotscot is offline hotscot  Scotland
diyAudio Member
 
Join Date: Aug 2004
Location: California
Default Definitive earthing advice sought.

Hi all
I have apparently successfully wired my center tap transformer to my rectifier board from my L3875 kit.
I'm obtaining plus and minus 38.2 V after rectification and without any load.

I really want to proceed very carefully here and I'm seeking advice on earthing my system. Again I have been reading through the forums and sometimes the advice is conflicting and or confusing.

From what I understand I connect the Greem/Yellow earth wire from my AC cord to my chassis. From this point I run a wire to CHG (Chassis Ground Connection) location on the amp boards.

(I should also place a fuse in series between the AC cord and the transformer.)

Ok so far?

Alan
  Reply With Quote
Old 13th September 2006, 07:54 PM   #2
Sherman is offline Sherman  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Chicago area
You've got it. The connection of the earth wire in your power cord to the chassis is often referred to as 'safety earth'.

One wire from that point to chassis ground on each amp board. Don't connect the chassis grounds of the two amp boards together then run a wire to your safety earth. Earth each board separately.

A fuse is definitely a must. For gainclones I generally use a 2 amp fuse, generally a 'Slo-Blo'. Put the fuse in line with the "hot" wire from the AC mains. Basically AC hot into chassis direct to the fuse, then from the fuse to the on/off switch then back to the rectifier board.
__________________
--Sherman
  Reply With Quote
Old 13th September 2006, 08:27 PM   #3
hotscot is offline hotscot  Scotland
diyAudio Member
 
Join Date: Aug 2004
Location: California
Basically AC hot into chassis direct to the fuse, then from the fuse to the on/off switch then back to the rectifier board. [/B][/QUOTE]


Just to clarify, do you mean AC to fuse to on/off switch then to transformer?

Thanks
Alan
  Reply With Quote
Old 15th September 2006, 12:08 AM   #4
Sherman is offline Sherman  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Chicago area
Good catch!

The AC hot coming in from the wall socket goes first to the fuse, then from the fuse to the switch and then from the switch to the power transformer NOT the rectifier board like I stated first.

My fault for trying to multitask while typing.
__________________
--Sherman
  Reply With Quote
Old 15th September 2006, 07:53 AM   #5
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
Alan, you many benefit from reading this !
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  Reply With Quote
Old 15th September 2006, 08:34 AM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
sorry to disagree and throw in another option.

The mains incomer should go;- Live to fuse to switch, Neutral to switch, Earth to chassis safety earth.

I think we are all agreed on this first bit.

You can use insulated terminal strips to help with these first interconnections, but try to keep the wires short and any that go wandering (to find a switch) should be double insulated.

Keep the safety earth beside the mains incomer.
Make it permanent.
NEVER dismantle the safety earth from the chassis when carrying out maintenance and/or testing and/or modification if there is ANY chance someone might plug the unit into the mains socket outlet.

Any additional connections to the safety earth must not require dismantling of the safety earth to chassis connection.

Now on to the audio ground.

I do not recommend direct connection from audio ground to safety earth.
I do recommend an indirect connection consisting of one/some/all of the following forming a parallel network. Some experimentation here may prove valuable.
The network can include:-
10r power resistor.
power bridge diode wired in inverse parallel.
high frequency capacitor (10nF to 100nF ceramic).
Ground lift switch (common in PA gear but generally not needed in domestic. Closing this switch often causes injection of hum and buzz into the amplfier)

The RCA input grounds should be isolated from the chassis.
All the amplifier grounds should be isolated from the chassis.
__________________
regards Andrew T.
  Reply With Quote
Old 15th September 2006, 12:40 PM   #7
Sherman is offline Sherman  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Chicago area
Quote:
Originally posted by AndrewT
[B]Hi,
sorry to disagree and throw in another option.

The mains incomer should go;- Live to fuse to switch, Neutral to switch, Earth to chassis safety earth.

I think we are all agreed on this first bit.

...
Andrew,

I agree a DPDT switch to switch both AC lines is the best setup.
About connecting signal ground to earth- it depends on where in the circuit we are. With chip amps it is pretty simple to have only one 'signal' ground that is floating. With tubes the concept of 'signal ground' is a bit more complex and there are areas where the signal ground will be earthed.
__________________
--Sherman
  Reply With Quote
Old 15th September 2006, 03:08 PM   #8
hotscot is offline hotscot  Scotland
diyAudio Member
 
Join Date: Aug 2004
Location: California
Guys...you'll understand now why I get confused.

If it makes it any easier I just want to make sure the box will be safe in the first instance. So I just need the simplest, safe, solution.

If there are different earthing configurations which affect sound quality I can explore those later as I learn more theory and practice.

(On a side point...in the UK we call the wires that come in on the ac mains cable Neutral, Live and Ground. In the US, where I am now, I guess it's Ground and what....Hot? For all practical purposes, being AC, do I just consider the two wires carrying the current as Hot relative to Ground?)

Regards
Alan
  Reply With Quote
Old 15th September 2006, 03:38 PM   #9
diyAudio Member
 
mrshow4u's Avatar
 
Join Date: Jul 2006
Hi HotScot, In the US if you have 2-wire, it's Hot and Neutral. Neutral connects to earth ground at the service box where power comes into the home.

For 3-wire, Hot, Neutral and ground.

Colors (US):
Hot = Black
Neutral = White
Ground = Green
__________________
".........These go to eleven"
  Reply With Quote
Old 15th September 2006, 05:07 PM   #10
ash_dac is offline ash_dac  United Kingdom
diyAudio Member
 
Join Date: Jan 2005
Location: UK
Quote:
Originally posted by AndrewT
Hi,

The RCA input grounds should be isolated from the chassis.
All the amplifier grounds should be isolated from the chassis.

If they wern't insulated would the RCA ground return (for a fault) current through any connected equipment ?

Note I also see numerous examples of mains powered amplifiers being tested on planks of wood.
  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
earthing advice on a US amp woodturner-fran Tubes / Valves 7 16th January 2009 12:25 AM
New Cabinet Opinions & Advice Sought Thomo Full Range 8 30th December 2008 11:03 PM
Fostex E16 advice sought john blackburn Analogue Source 0 18th September 2007 08:58 PM
Woofer advice sought cs Multi-Way 7 29th January 2007 09:08 PM
HiFi Advice sought Gina Everything Else 80 11th December 2002 02:19 PM


New To Site? Need Help?

All times are GMT. The time now is 03:09 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