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View Poll Results: Was a good idea to use two lm1875 or a big stk chip
Use stk 8 27.59%
use lm1875 21 72.41%
Voters: 29. You may not vote on this poll

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Old 8th January 2013, 11:50 AM   #41
blu_glo is offline blu_glo  England
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Your heatsink pictured is inadequate; it has to be much more substantial or the chip will shutdown automatically or otherwise fail!
Start with something 70x90x50mm long fins and keep supply rails as low as possible for desired output power.

Last edited by blu_glo; 8th January 2013 at 12:09 PM. Reason: typo
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Old 8th January 2013, 12:07 PM   #42
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by picowallspeaker View Post
55 and 21 W don't exist as values for 'old type' lightbulbs
I know 25 and 60 W ratings ! So, are you sure that you are referring to
the classic lightbulbs, and not the electronic ones ?
Same for the power supply

RE: I blew those crappy speakers from the moment I see
car lamps 55w for headlights and 21w for the back
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Old 8th January 2013, 12:07 PM   #43
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by blu_glo View Post
Your heatsink pictures is inadequate; it has to be much more substantial or the chip will thermally runaway or fail! Start with something 70x90x50mm long fins and keep supply rails as low as possible for desired output power.
That was just for a test at 12v how many times do i have to say it
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Old 8th January 2013, 12:17 PM   #44
PetruV is offline PetruV  Romania
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I have built the schematic for lm from the datasheetand the speaker goes up and i hear lots of weird noises with noting hooked up to it
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Old 8th January 2013, 12:19 PM   #45
PetruV is offline PetruV  Romania
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powered from +- 12v
If i connect a wire from ground to in the weird noises stop and the speaker just goes down with no weird noises
May this be because i havent used the 1m resistor on input or that i used 22k instead of 20k from out to inverting input
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Last edited by PetruV; 8th January 2013 at 12:39 PM.
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Old 8th January 2013, 12:51 PM   #46
blu_glo is offline blu_glo  England
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" That was just for a test at 12v how many times do i have to say it "

You don't mention the 12V untill someone appears to guess it about 1/3 of the way through the posts, or have you edited them, I see no previous mention of the actual rail value?

Even at lowish +/- 12V split supply you will need Proper heatsinking regardless, it takes too much quiescent power to dissipate without heatsink!

Last edited by blu_glo; 8th January 2013 at 12:53 PM.
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Old 8th January 2013, 12:59 PM   #47
PetruV is offline PetruV  Romania
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Quote:
Originally Posted by blu_glo View Post
" That was just for a test at 12v how many times do i have to say it "

You don't mention the 12V untill someone appears to guess it about 1/3 of the way through the posts, or have you edited them, I see no previous mention of the actual rail value?

Even at lowish +/- 12V split supply you will need Proper heatsinking regardless, it takes too much quiescent power to dissipate without heatsink!
It was just for couple second long test
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Old 8th January 2013, 01:00 PM   #48
PetruV is offline PetruV  Romania
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On the tda i get signal just from one chanel and very distorted
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Old 8th January 2013, 01:08 PM   #49
PetruV is offline PetruV  Romania
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Just added the 1m resistor to the lm and the weird noises are gone,but the speaker now goes down with nothing hooked up ,could this speaker going down problem be because from output to inverting input i used 22k instead of 20k
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Old 8th January 2013, 01:14 PM   #50
blu_glo is offline blu_glo  England
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I did build a pair of these LM1875 up on some old maplin pcbs I just happened to have lying around some years back.
Using a 30VA 18-0-18V transformer managed to cram complete circuit and mains power supply all into a Hammond extruded case and made 2 off monoblocks as such.
I can send pics if interested.
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