XLR Pin#1 problem - Bridged LM4780 - Page 2 - diyAudio
Go Back   Home > Forums > Commercial Sector > Vendor Forums > Audio Sector

Audio Sector Kits & PC boards from AudioSector

Reply
 
Thread Tools Search this Thread
Old 30th August 2009, 10:19 PM   #11
GAH is offline GAH  Fiji
diyAudio Member
 
Join Date: Apr 2009
Default Pin #1 problem

After further investigation I found the 10 ohm resistor had become disconnected from the chassis earth. This explains why I had to connect Pin #1 to Chassis and Signal Grd to eliminate hum from my amp. Now with the 10 ohm resistor properly connected to chassis earth (from power star) and Pin#1 connected ONLY to signal ground as you stated I'm hum free. All is sounding well.

Peter, thanks again for your help.
  Reply With Quote
Old 30th August 2009, 10:39 PM   #12
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
There was a similar discussion on a subject here: XLR Pin 1 question - chassis vs circuit ground
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
  Reply With Quote
Old 30th August 2009, 10:40 PM   #13
diyAudio Member
 
Join Date: Jan 2004
Location: Toronto, ON, Canada
Hm. I thought the proper way to do it was to connect pin 1 to chassis on both sides and then connect signal ground to chassis at only one point (star) through a disconnecting network/loop breaker circuit.
  Reply With Quote
Old 23rd September 2009, 10:52 PM   #14
GAH is offline GAH  Fiji
diyAudio Member
 
Join Date: Apr 2009
Default 10R break resistor - Why is necessary?

The chassis is connected to power entry module Earth ground and the center of copper wire between the OGs (of both amp boards) connects to chassis through 10R resistor.[/QUOTE]

Peter, why is the 10R resistor necessary? By including such a resistor is there any compromise to safety should a power fault occur?

Regards
Glen
  Reply With Quote
Old 24th September 2009, 12:03 AM   #15
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
This is to separate signal and AC line grounds. 10R resistor isn't neccessary, I've built amps without it and they worked equally well.

What kind of power faults do you have in mind?
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
  Reply With Quote
Old 24th September 2009, 12:50 AM   #16
GAH is offline GAH  Fiji
diyAudio Member
 
Join Date: Apr 2009
Thanks Peter

Andrew T made a comment about safety when using a break resistor. See below. What's your opinion on this?

The 6ohm disconnecting resistor between Safety Earth (chassis) and Audio Ground (Star Ground) does not comply with the mains safety requirement of most countries.

The exposed conductive parts must be permanently connected to the Safety Earth.

The reason for this requirement is to ensure that the mains fuse blows quickly, if the mains live lead during a fault condition contacts and/or connects to other low voltage parts of the equipment.
If fault current prior to the fuse blowing passes from Live to Audio ground then through the 6ohm resistor to Safety Ground back to distribution board earth the voltage appearing on the audio ground will be high enough to kill anyone that happened to touch the equipment at the wrong time. Further, fault current passing through the resistor will more likely blow the resistor before it blows the fuse, leaving the Audio ground at Live voltage and no effective connection to Safety Earth.

I recommend either of two solutions.
The first and safest is direct connection from Safety Earth to Audio Ground. This generally gives rise to hum loops in most connected equipment.
The alternative is to use a Disconnecting Network between Audio Ground and Safety Earth. This Disconnecting Network can consist of a parallel combination of:- Power resistor, inverse parallel coupled Power diodes, Power Thermistor, HF capacitor.
The Disconnecting Network MUST survive LONGER than it takes the mains fuse to rupture and for the arc to extinguish.
  Reply With Quote
Old 24th September 2009, 01:22 AM   #17
diyAudio Member
 
Peter Daniel's Avatar
 
Join Date: Jul 2002
Location: Toronto, Canada
Send a message via AIM to Peter Daniel
If a resistor does not comply with the mains safety regulations of your country, use thermistor, like it's done in First Watt amps (CL60).

You can also connect directly safety ground to audio ground or use disconnecting network as Andrew recommends.

If you check my official GC building guide, you will notice that I actually recommend thermistor or Disconnecting Network:

http://www.diyaudio.com/forums/audio-sector/123003-commercial-gainclone-kit-building-instructions-post1518378.html

The resistor is for the brave ones only
__________________
www.audiosector.com
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

Last edited by Peter Daniel; 24th September 2009 at 01:30 AM.
  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
Bridged LM4780 Amp jackinnj Chip Amps 19 2nd November 2012 04:17 PM
Lm4780 Bridged PCB Baracus Chip Amps 8 7th January 2006 12:45 AM
Bridged Lm4780. Up and running! sachi Chip Amps 5 14th December 2005 04:37 PM
Trying to understand the LM4780 bridged amp... youyoung21147 Chip Amps 27 23rd October 2005 07:41 PM
Bridged lm4780 rs1026 Chip Amps 2 12th September 2004 10:49 AM


New To Site? Need Help?

All times are GMT. The time now is 07:17 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