another Hum issue LM3875

sts9fan · 20th August 2007, 09:04 PM

So I have built up the first channel for my stereo LM3875 kit from audiosector. I decided to test it out and see if it works and it does but it is also humming like crazy. I currently only have the safety ground hooked up. The signal ground is not connected. It also has the hum with no source connected. I tried a cheater plug (not to use just as a test) and the hum was still there.
Now I generally have no idea what i am doing so I am not sure how to test this thing. I am not sure where to take measurements to see if I am getting proper voltage etc. Any help would be great.
Thanks
Kris

BWRX · 21st August 2007, 12:33 AM

The source/signal ground needs to be connected to the power ground.

sts9fan · 21st August 2007, 02:48 PM

thanks I will try that today

Peter Daniel · 21st August 2007, 03:00 PM

You may find some info how to wire the kit here:
http://www.diyaudio.com/forums/showt...20#post1108820
http://www.diyaudio.com/forums/showt...773#post787773

sts9fan · 21st August 2007, 03:23 PM

Looks like the only thing I have different is I don't have the chassis ground connected. Could this be the cause of the hum? If I connect it and it is still humming what should I look at next?

thanks

Nordic · 21st August 2007, 05:48 PM

Make sure input RCA sockets are isolated from case...

traw · 22nd August 2007, 04:36 AM

take a snapshot of your connections - it will be easier to see. lack of chassis connection likely not cause, the center tap or shared ground from the transformer anchors the 0V.

sts9fan · 22nd August 2007, 12:56 PM

will do thanks. The transformer I am using is a AnTek AN-3222
http://toroid-transformer.com/

sts9fan · 28th August 2007, 09:02 PM

Here are some pictures. Hopefully they can help.

Thanks for any help!

Kris

sts9fan · 28th August 2007, 09:41 PM

http://travel.webshots.com/photo/222...86056042namwJw

20th August 2007, 09:04 PM	#1
sts9fan diyAudio Member Join Date: Apr 2006 Location: MA	another Hum issue LM3875 So I have built up the first channel for my stereo LM3875 kit from audiosector. I decided to test it out and see if it works and it does but it is also humming like crazy. I currently only have the safety ground hooked up. The signal ground is not connected. It also has the hum with no source connected. I tried a cheater plug (not to use just as a test) and the hum was still there. Now I generally have no idea what i am doing so I am not sure how to test this thing. I am not sure where to take measurements to see if I am getting proper voltage etc. Any help would be great. Thanks Kris

21st August 2007, 12:33 AM	#2
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	The source/signal ground needs to be connected to the power ground. __________________ Brian

21st August 2007, 03:00 PM	#4
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	You may find some info how to wire the kit here: http://www.diyaudio.com/forums/showt...20#post1108820 http://www.diyaudio.com/forums/showt...773#post787773 __________________ 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

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21st August 2007, 02:48 PM	#3
sts9fan diyAudio Member Join Date: Apr 2006 Location: MA	thanks I will try that today

21st August 2007, 03:23 PM	#5
sts9fan diyAudio Member Join Date: Apr 2006 Location: MA	Looks like the only thing I have different is I don't have the chassis ground connected. Could this be the cause of the hum? If I connect it and it is still humming what should I look at next? thanks

21st August 2007, 05:48 PM	#6
Nordic diyAudio Member Join Date: Sep 2005	Make sure input RCA sockets are isolated from case...

22nd August 2007, 04:36 AM	#7
traw diyAudio Member Join Date: Sep 2005	take a snapshot of your connections - it will be easier to see. lack of chassis connection likely not cause, the center tap or shared ground from the transformer anchors the 0V.

22nd August 2007, 12:56 PM	#8
sts9fan diyAudio Member Join Date: Apr 2006 Location: MA	will do thanks. The transformer I am using is a AnTek AN-3222 http://toroid-transformer.com/

28th August 2007, 09:02 PM	#9
sts9fan diyAudio Member Join Date: Apr 2006 Location: MA	Here are some pictures. Hopefully they can help. Thanks for any help! Kris

28th August 2007, 09:41 PM	#10
sts9fan diyAudio Member Join Date: Apr 2006 Location: MA	http://travel.webshots.com/photo/222...86056042namwJw

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