chipamp.com LM1875 Hmm

pclements · 12th February 2009, 03:15 AM

I constructed a LM1875 kit from chipamp.com. I assembled and tested it per the instuctions listed here on DIYAudio.com.
Finally made a LM1875 amp

The PSU tests OK, correct DC voltage. I measure NO DC-offset at the amp output. When connected to my system it produces only a loud hum and no music. I've checked everything I can think of, but find no discrpencies between the as-assembled amp and the instructions.

Anyone have any suggestions? Further testing I should do?

Thanks,

pacificblue · 12th February 2009, 04:57 AM

Pictures?

mjf · 12th February 2009, 06:47 AM

hello.
no dc-offset? there are mostly a few milivolts of offset.........
perhaps check the input for a missing or wrong ground connection,cable failure or so...........
greetings.............

peranders · 12th February 2009, 07:04 AM

If you take your DVM and measure the resistance between signal ground, speaker ground and power ground, are they connected?

Brian, don't you have schematics over your design? Doesn't your cad program support that?

fr1s · 13th February 2009, 06:38 AM

Quote:

Originally posted by pclements
I constructed a LM1875 kit from chipamp.com. I assembled and tested it per the instuctions listed here on DIYAudio.com.
Finally made a LM1875 amp

The PSU tests OK, correct DC voltage. I measure NO DC-offset at the amp output. When connected to my system it produces only a loud hum and no music. I've checked everything I can think of, but find no discrpencies between the as-assembled amp and the instructions.

Anyone have any suggestions? Further testing I should do?

Thanks,

I have same problem :/

audio1st · 13th February 2009, 05:18 PM

Please give info on, C1, C2 and R6 values used.
Remember these locations must be bridged (jumped), if you choose to omit them..

pclements · 17th February 2009, 03:01 AM

Thanks for the suggestions... My R6 jumper was the problem. Now everything sounds AWESOME. It runs hot, but I'll get that fixed.

Thanks for the help.

-Patrick-

Comitex · 18th February 2009, 03:53 PM

may i ask how much power can you get from this amp ?

Stixx · 19th February 2009, 01:52 PM

Just google for LM1875 and there you are...
20W into 4 ohms

Luck · 21st February 2009, 06:48 AM

Hi,try to use +/-28V if your heatsink is big enough.... you will hear a differnce sound compare with your +/- 25V system.

12th February 2009, 03:15 AM	#1
pclements diyAudio Member Join Date: Oct 2007	chipamp.com LM1875 Hmm I constructed a LM1875 kit from chipamp.com. I assembled and tested it per the instuctions listed here on DIYAudio.com. Finally made a LM1875 amp The PSU tests OK, correct DC voltage. I measure NO DC-offset at the amp output. When connected to my system it produces only a loud hum and no music. I've checked everything I can think of, but find no discrpencies between the as-assembled amp and the instructions. Anyone have any suggestions? Further testing I should do? Thanks,

12th February 2009, 04:57 AM	#2
pacificblue diyAudio Member Join Date: May 2008	Pictures? __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

12th February 2009, 07:04 AM	#4
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	If you take your DVM and measure the resistance between signal ground, speaker ground and power ground, are they connected? Brian, don't you have schematics over your design? Doesn't your cad program support that? __________________ /Per-Anders (my first name) or P-A as my friends call me

17th February 2009, 03:01 AM	#7
pclements diyAudio Member Join Date: Oct 2007	Fixed IT! Thanks for the suggestions... My R6 jumper was the problem. Now everything sounds AWESOME. It runs hot, but I'll get that fixed. Thanks for the help. -Patrick-

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12th February 2009, 06:47 AM	#3
mjf diyAudio Member Join Date: Jan 2009 Location: upper austria/near linz	hello. no dc-offset? there are mostly a few milivolts of offset......... perhaps check the input for a missing or wrong ground connection,cable failure or so........... greetings.............

13th February 2009, 05:18 PM	#6
audio1st diyAudio Member Join Date: May 2005 Location: Foxton, CAMBS..	Please give info on, C1, C2 and R6 values used. Remember these locations must be bridged (jumped), if you choose to omit them..

18th February 2009, 03:53 PM	#8
Comitex diyAudio Member Join Date: Feb 2009	may i ask how much power can you get from this amp ?

19th February 2009, 01:52 PM	#9
Stixx diyAudio Member Join Date: Sep 2003 Location: Southern Germany	Just google for LM1875 and there you are... 20W into 4 ohms

21st February 2009, 06:48 AM	#10
Luck diyAudio Member Join Date: Jul 2006	Hi,try to use +/-28V if your heatsink is big enough.... you will hear a differnce sound compare with your +/- 25V system.

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