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Old 12th February 2009, 03:15 AM   #1
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Default 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,
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Old 12th February 2009, 04:57 AM   #2
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Old 12th February 2009, 06:47 AM   #3
mjf is offline mjf  Austria
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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.............
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Old 12th February 2009, 07:04 AM   #4
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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?
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Old 13th February 2009, 06:38 AM   #5
fr1s is offline fr1s  Canada
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Default Re: chipamp.com LM1875 Hmm

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 :/
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Old 13th February 2009, 05:18 PM   #6
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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..
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Old 17th February 2009, 03:01 AM   #7
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Default 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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Old 18th February 2009, 03:53 PM   #8
Comitex is offline Comitex  Slovenia
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may i ask how much power can you get from this amp ?
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Old 19th February 2009, 01:52 PM   #9
Stixx is offline Stixx  Germany
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Just google for LM1875 and there you are...
20W into 4 ohms
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Old 21st February 2009, 06:48 AM   #10
Luck is offline Luck  China
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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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