Grounding chipamp 3875

marcus7601 · 7th April 2009, 07:44 PM

I need help with connecting my chipamp-kit, LM3875. The problem i have is that my volume pot is not working. On no volume, i still hear normal level and if i raise volume it goes up very quickly.

I have a chipamp.com kit with a CT Transformer. I have enclosed a quick drawing of my setup. Since i have a wodden chassi, i have serial connected all input rca grounds and runs them pass the rotary switch directly to SG.

Any help for a newbie?

Please excuse my simple drawing...

AndrewT · 8th April 2009, 10:47 AM

I need more info.
can you colour or or identify the signal lines differently from the return lines?
Can you add on the other ground/return lines connected to the amp PCB?
Can you confirm how you have connected the pot/attenuator?

Is chipamp an inverting topology?
Can you link to a schematic?

marcus7601 · 9th April 2009, 08:42 PM

The problem is that my volume pot (50k log) is measuring 14k when fully turned to zero. So i still here music.

The ground from pot goes to SG on PCB, same as input gnd.

I dont have schematic for Audiosector kit.

pacificblue · 9th April 2009, 10:34 PM

50k becomes 14k at zero position? Either the potentiometer is broken or you connected it in parellel to the 20k input resistor and the wrong way round.

Here is your schematic. How can you build an amplifier without a schematic?

AndrewT · 9th April 2009, 11:31 PM

A newbie should not be building a DC coupled amplifier.

Be very careful you don't burn out your speakers.

Peter Daniel · 9th April 2009, 11:45 PM

Your basic schematic seems to be fine. Why don't you look through this thread: http://www.diyaudio.com/forums/showt...97#post1516297 Everything has been explained there.

ratza · 10th April 2009, 01:16 PM

Linear pot, maybe?

marcus7601 · 10th April 2009, 07:27 PM

The pot is fine, it measures fine when disconnected.

The main thing i supspect is the grounding of the amp boards.

Peter - when using a centertapped transformer, the centertap goes to PG+, Then i only have 2 PG- and one PG+ left. Should i only use one PG+ per board and thats it?

Peter Daniel · 10th April 2009, 08:13 PM

With CT transformer you need to modify the bridges; it's been explained here: http://www.diyaudio.com/forums/showt...83#post1196283

pacificblue · 10th April 2009, 10:10 PM

Quote:

Originally posted by marcus7601
The pot is fine, it measures fine when disconnected.

Quote:

Originally posted by pacificblue
you connected it in parallel to the 20k input resistor and the wrong way round.

50k || 20k = 14,3k

Desolder the 20k input resistor and check again. If it works, replace the potentiometer with a 20-25k type for better CMRR.

8th April 2009, 10:47 AM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I need more info. can you colour or or identify the signal lines differently from the return lines? Can you add on the other ground/return lines connected to the amp PCB? Can you confirm how you have connected the pot/attenuator? Is chipamp an inverting topology? Can you link to a schematic? __________________ regards Andrew T.

9th April 2009, 10:34 PM	#4
pacificblue diyAudio Member Join Date: May 2008	50k becomes 14k at zero position? Either the potentiometer is broken or you connected it in parellel to the 20k input resistor and the wrong way round. Here is your schematic. How can you build an amplifier without a schematic? __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

9th April 2009, 11:31 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	NIGC = DC coupled A newbie should not be building a DC coupled amplifier. Be very careful you don't burn out your speakers. __________________ regards Andrew T.

9th April 2009, 11:45 PM	#6
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	Your basic schematic seems to be fine. Why don't you look through this thread: http://www.diyaudio.com/forums/showt...97#post1516297 Everything has been explained there. __________________ 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

10th April 2009, 01:16 PM	#7
ratza diyAudio Member Join Date: Dec 2007 Location: Sibiu, Romania	Linear pot, maybe? __________________ Any solution is a compromise.


	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

10th April 2009, 07:27 PM	#8
marcus7601 diyAudio Member Join Date: Jun 2006	The pot is fine, it measures fine when disconnected. The main thing i supspect is the grounding of the amp boards. Peter - when using a centertapped transformer, the centertap goes to PG+, Then i only have 2 PG- and one PG+ left. Should i only use one PG+ per board and thats it?

10th April 2009, 08:13 PM	#9
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	With CT transformer you need to modify the bridges; it's been explained here: http://www.diyaudio.com/forums/showt...83#post1196283 __________________ 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

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

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
FS chipamp 3386, 3875, 1 enclosure	wendell	Swap Meet	4	15th June 2008 03:06 PM
Dual-mono chipamp (3886) problem - possible grounding issue	phresh	Chip Amps	31	29th February 2008 03:50 PM
Preventing a 3875 chipamp from blowing tweeters	bcdzt5	Chip Amps	8	6th February 2008 07:23 PM
Recommended UK transformer for 3875 chipamp?	Colin	Chip Amps	6	1st March 2007 08:02 PM
Chipamp.com pcb with linkwitz 3875 design	akunec	Chip Amps	3	7th June 2005 07:06 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