lm3875 question

Jamh · 29th December 2008, 08:45 AM

I'm having a strange problem with a gainclone I jut built. When I first power it up, it sounds great, but then after a couple of seconds a fuzzy distortion sets in both channels. If I power off and back on, the same thing happens. The heat sinks are not too hot. Any ideas what it could be?

This is the first time I'm using non-insulated chips. I have properly insulated them with mica. No shorts anywhere.

AndrewT · 29th December 2008, 08:50 AM

Hi,
how hot is the chipamp?
Could any of the polarised caps be back to front?
Are you still running it through a bulb tester?

lineup · 29th December 2008, 08:55 AM

Could it be oscillations at output?
What schematic did you use?

Jamh · 29th December 2008, 04:21 PM

caps are good. I have:
1 to + 1000uf
4 to - 1000uf
3 to out
7 to 178 ohm to 21k (parallel)
8 to 730 (parallel) to 21k (nfb)

Perhaps I should try a resistor at the output?

29th December 2008, 08:45 AM	#1
Jamh diyAudio Member Join Date: Dec 2003 Location: sacramento	lm3875 question I'm having a strange problem with a gainclone I jut built. When I first power it up, it sounds great, but then after a couple of seconds a fuzzy distortion sets in both channels. If I power off and back on, the same thing happens. The heat sinks are not too hot. Any ideas what it could be? This is the first time I'm using non-insulated chips. I have properly insulated them with mica. No shorts anywhere.

29th December 2008, 08:50 AM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, how hot is the chipamp? Could any of the polarised caps be back to front? Are you still running it through a bulb tester? __________________ regards Andrew T.

29th December 2008, 08:55 AM	#3
lineup diyAudio Member Join Date: Dec 2005 Location: the north	Could it be oscillations at output? What schematic did you use? __________________ lineup

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29th December 2008, 04:21 PM	#4
Jamh diyAudio Member Join Date: Dec 2003 Location: sacramento	caps are good. I have: 1 to + 1000uf 4 to - 1000uf 3 to out 7 to 178 ohm to 21k (parallel) 8 to 730 (parallel) to 21k (nfb) Perhaps I should try a resistor at the output?

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