LM3875 Ground Points

mahenreddy · 19th October 2009, 01:48 PM

I am building a LM3875 based amp and looked at various PCB layouts and they don't some to be consistent w.r.t the ground point that is from the junction of non inverting (Pin 8) input to ground through resistor (1K) and capacitor(22uf). Some are treating this as signal ground and some are connecting it directly to the power ground. Is this a signal ground or power ground?

hybridfiat · 19th October 2009, 10:57 PM

Quote:

Originally Posted by mahenreddy

I am building a LM3875 based amp and looked at various PCB layouts and they don't some to be consistent w.r.t the ground point that is from the junction of non inverting (Pin 8) input to ground through resistor (1K) and capacitor(22uf). Some are treating this as signal ground and some are connecting it directly to the power ground. Is this a signal ground or power ground?

As I understand it (and I stand ready to be corrected) if you are using a single powerboard and transformer the ground is common to all; signal, power and output. It is termed a "star earth/ground", because of it's appearance.
Using this form of common earth is the best way to eliminate hum and buzz at idle.
See Peter Daniels thread here Commercial Gainclone kit- building instructions Good luck and happy soldering

hybridfiat · 01:07 AM

Have a look at this. The extra circuit is a ground breaker to prevent damage from power supply failure and overvoltage. See Power Star Earth with Ground Breaker Rod Elliott of ESP

hybridfiat · 21st October 2009, 02:07 AM

The audio out ground leads can be sent directly to the star earth (instead of the board) as well if that is convenient

sangram · 21st October 2009, 07:41 AM

Ri/Ci is signal ground, it's a low-level signal.

when I construct on P2P, I return it separately to the ground point.

The entry of the power lead to the chip is what I consider the star ground, and all three current paths are returned separately to it - input ground, feedback ground and speaker output, taking care to see that the path of speaker current does not meet any of the other two grounds. Gets a little complicated with multiple chips setups, but I manage.

19th October 2009, 01:48 PM	#1
mahenreddy diyAudio Member Join Date: Oct 2003 Location: Hyderabad	LM3875 Ground Points I am building a LM3875 based amp and looked at various PCB layouts and they don't some to be consistent w.r.t the ground point that is from the junction of non inverting (Pin 8) input to ground through resistor (1K) and capacitor(22uf). Some are treating this as signal ground and some are connecting it directly to the power ground. Is this a signal ground or power ground?

21st October 2009, 02:07 AM	#4
hybridfiat diyAudio Member Join Date: May 2008	The audio out ground leads can be sent directly to the star earth (instead of the board) as well if that is convenient __________________ Entia non sunt multiplicanda praeter neccissitatem

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Star points & Ground Planes.	underwurlde	Power Supplies	8	24th May 2008 11:08 PM
Parallel LM3886, input ground, power ground, safety resistor and oscillations.	markiemrboo	Chip Amps	5	9th August 2007 03:50 PM
DC filament ground and high voltage ground	mikeyho	Tubes / Valves	0	15th September 2005 05:52 PM
does connecting mains ground with circuit ground create a ground loop?	jarthel	Everything Else	0	25th June 2003 12:55 PM
Should I directly connect my signal ground to chassis ground?	Bricolo	Solid State	3	28th February 2003 05:31 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

21st October 2009, 07:41 AM	#5
sangram diyAudio Member Join Date: Sep 2002 Location: India	Ri/Ci is signal ground, it's a low-level signal. when I construct on P2P, I return it separately to the ground point. The entry of the power lead to the chip is what I consider the star ground, and all three current paths are returned separately to it - input ground, feedback ground and speaker output, taking care to see that the path of speaker current does not meet any of the other two grounds. Gets a little complicated with multiple chips setups, but I manage.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)