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Old 6th October 2014, 05:39 PM   #1
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Default please review this pcb design

i am trying to make an lm1875 based amp. I plan to use an 18v trafo with this. I am attaching the schematic and board images, could someone please review it and provide tips/suggestions to improvise it.
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File Type: png board.png (136.2 KB, 366 views)
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Old 6th October 2014, 05:42 PM   #2
rayma is online now rayma  United States
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Quote:
Originally Posted by doors666 View Post
i am trying to make an lm1875 based amp. I plan to use an 18v trafo with this. I am attaching the schematic and board images, could someone please review it and provide tips/suggestions to improvise it.
A series R is needed at IN-1 for the 220pF to act as a filter.
More importantly, the NFB loop to the negative input is connected wrongly. See the TI app note, p.2.

http://www.ti.com/lit/ds/symlink/lm1875.pdf

Last edited by rayma; 6th October 2014 at 05:49 PM.
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Old 6th October 2014, 06:17 PM   #3
mjf is offline mjf  Austria
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i think the electrolytics C12,C15 (2200uF) are built in wrong (reverted)........
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Old 6th October 2014, 06:19 PM   #4
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thanx, good catch on the nfb... fixed.. attaching new images..
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Old 6th October 2014, 06:29 PM   #5
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Originally Posted by mjf View Post
i think the electrolytics C12,C15 (2200uF) are built in wrong (reverted)........
yeah, the polarity is wrong on those. fixed..
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Old 6th October 2014, 06:30 PM   #6
rayma is online now rayma  United States
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Quote:
Originally Posted by doors666 View Post
thanx, good catch on the nfb... fixed.. attaching new images..
Looks like you should use non-polarized electrolytics in the NFB loop.
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Old 6th October 2014, 06:31 PM   #7
Vasquo is offline Vasquo  United States
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As mjf pointed out, C11 and C14 (on post #4) are backwards. (+) should be connected to GND.
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Old 7th October 2014, 05:36 AM   #8
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Originally Posted by rayma View Post
Looks like you should use non-polarized electrolytics in the NFB loop.
the datasheet shows polarized cap.

The board looks ok?

Last edited by doors666; 7th October 2014 at 05:43 AM.
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Old 7th October 2014, 05:53 AM   #9
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I see two output pins for the +ve speaker side, but nothing for the speaker return.
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Old 7th October 2014, 05:57 AM   #10
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Originally Posted by abraxalito View Post
I see two output pins for the +ve speaker side, but nothing for the speaker return.
that i plan to bring to the main ground point, the point where the chassis is grounded. the mains socket earth, speaker return, pcb ground points, all of these will be bolted to the chassis.
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