understanding star grounding - Page 12 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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 26th December 2008, 09:09 PM   #111
diyAudio Member
 
Join Date: May 2008
Quote:
Originally posted by AndrewT
Pacific,
would you care to comment?
Hi, Andrew,

My post answered post #105 and its attached schematic, not #108.

Post #108 is one example, where the poster must find the best compromise whether the advantages of shielding the signal wires are bigger than the disadvantages of increasing the capacity between signal wires and ground. Or maybe the increased capacity is also an advantage, because it could accidentally create a convenient RF-filter. There is too little and too imprecise data to decide that from a distance.

Although there is a small possibility that this schematic could lead to hum. If there is a star-point for signal return on the PCB (signal ground, IN- or whatever it is called there), the potentiometer's gound wire and the RCA's ground wire should go there individually and both be connected to that point.

From the feedback circuit's point of view it is also better to connect the speaker return to the PCB's ground. That entails however sufficiently big traces one the PCB for the current involved.

Regards
David
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 30th December 2008, 11:03 PM   #112
endia is offline endia  Turkey
diyAudio Member
 
Join Date: Sep 2004
Location: istanbul
hi,
what type of capacitor should i use for 100 nf in Rod Elliot's article?
http://sound.westhost.com/earthing.htm
ordinary film or polyester caps are sufficient or should i use class X2 type?
and also what is the voltage rating for this cap?
thanks..
  Reply With Quote
Old 31st December 2008, 08:11 AM   #113
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
if the diodes are doing their job to pass peak and fault currents then the cap should never see more than a few volts.
I have used both ceramic 50V and MKT 100V in this location. It seems to make no audible difference and I cannot see a safety issue with using 25V here.
__________________
regards Andrew T.
  Reply With Quote
Old 31st December 2008, 08:40 AM   #114
diyAudio Member
 
Join Date: May 2008
A ceramic or normal film capacitor will be sufficient as long as the bridge rectifier is either working normally or internally shorted. If the unlikely event of a phase to amplifier ground short ocurrs at the same time as the even more unlikely event of an internally open-circuited bridge rectifier, the 10 Ohm resistor will go up in flames anyhow and it doesn't matter, if the capacitor does the same or not.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 31st December 2008, 09:28 AM   #115
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally posted by pacificblue
....as long as the bridge rectifier is either working normally or internally shorted. If the unlikely event of a phase to amplifier ground short occurs at the same time as the even more unlikely event of an internally open-circuited bridge rectifier,........
I bit the bullet and tested a similar arrangement to the ESP Disconnecting Network.
Wired the mains Live from the fused IEC socket to the network with the other side of the Network to Safety Earth.
I blew the fuse holder apart when I switched on. The majority of the glass and copper fuse disappeared with a big bang.
The Network components measured as unaffected by the Fault current and looked unaffected.
__________________
regards Andrew T.
  Reply With Quote
Old 31st December 2008, 12:45 PM   #116
diyAudio Member
 
Join Date: May 2008
Yes, I didn't want to give another impression. It is so unlikely that four high current diodes go open circuit at the same time, even Murphy's Law may not apply anymore.

If the rectifier is internally shorted, there is virtually no voltage across the resistor and capacitor, so any resistor and capacitor would probably live forever on that condition.

And if the rectifier is in working condition you will get 1 or 2 V across them until the fuse reacts. You could probably even get away with a 1 W resistor and a 6 V capacitor there.

A 35 A bridge rectifier usually survives several 100 A of short circuit current per diode, before it fails. This circuit is as safe as you can reasonably design one.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 8th January 2009, 09:25 PM   #117
endia is offline endia  Turkey
diyAudio Member
 
Join Date: Sep 2004
Location: istanbul
hi,
i'm getting a little obssesive about safety earthing nowadays.
and a bit confused between these two schemas..

in digi's schema safety earth is bonded to chassis..

http://www.diyaudio.com/forums/attac...amp=1213600606

but in original network schema, safety earth is going to rectifier's shorted ac legs..

http://sound.westhost.com/earthing.htm

are these two wiring same? or am i missing something?
thanks a lot..
  Reply With Quote
Old 9th January 2009, 08:38 AM   #118
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
the first is wrong it shows the Safety Earth going to a terminal block and from the Terminal block to chassis.

The second is correct but misleading.
It shows the Safety Earth going straight to chassis but the diagram implies it could come off the terminal of the rectifier.

All exposed conductive materials must be permanently connected to Safety Earth.

Take the Safety Earth wire direct to chassis with a short robust mechanical fixture, or even welded but not soldered.

From above the permanent fixture take a connection from the Safety Earth to the Audio Ground. This can be a direct wire connection or as shown in fig2 of ESP through a Disconnecting Network.
BUT,
that connecting wire and/or Disconnecting Network must survive longer than it takes the mains fuse to rupture and for the arc to extinguish. This fault current can run to kA.
The bigger the mains fuse the longer it takes to disconnect the fault.
__________________
regards Andrew T.
  Reply With Quote
Old 9th January 2009, 11:23 AM   #119
diyAudio Member
 
Juergen Knoop's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
Question no soldering?

be careful with spade connectors!
Last year I opened a >10 year old amplifier and found that the 6,3mm spade connectors had lost their contact force.
Lots of mains jacks, filters and rectifiers come with spade connectors.
regards
  Reply With Quote
Old 9th January 2009, 11:39 AM   #120
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
I don't count a spade connector as permanent!
__________________
regards Andrew T.
  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
Quick question about star grounding jn2630 Tubes / Valves 8 21st January 2008 01:31 AM
Question about Star Grounding voivodata Tubes / Valves 2 20th March 2007 07:46 PM
star grounding with a seperate PSu Rafal Chip Amps 6 29th October 2006 07:16 AM
Star Grounding Questions LHMAudio Solid State 5 12th May 2006 04:31 PM
Star grounding in PSU alexl Power Supplies 10 7th April 2005 08:46 PM


New To Site? Need Help?

All times are GMT. The time now is 09:48 PM.


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