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Old 26th April 2011, 10:10 AM   #1
add is offline add  India
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Default LM 1875 stereo amplifier

when i switch on the circuit it works fine but after few seconds it goes dead ,
when i switch it off and switch on it immediately then also it's dead but i switch on after 5 - 10 seconds then it works finely but again same thing happens

i have attached a thick aluminum plate for heat sink

can the problem be because of slew rate of TL072 ic
(the slew rate is 13V/us ) or whether the circuit starts to oscillating.
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Old 26th April 2011, 01:53 PM   #2
sregor is offline sregor  United States
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Why R3? If you turn your bridge circuit on it causes half the supply voltage to go to the inverting amp. Tryit without - maybe lowering r4 to something lower. Does it work in normal (non bridged) mode? (my guess would be something is drifting to one of the supply voltages, then no signal goes through). Slew rate of op amp shouldn't cause problems in itself - worry about supply bypassing, layout and ground connections. Good luck.
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Old 26th April 2011, 03:03 PM   #3
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This is three times in two different threads that people have told you to remove R3. Why don't you just try it?

:)ensen.
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Old 26th April 2011, 03:22 PM   #4
lineup is offline lineup  Sweden
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... and remove R17, as well
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Old 27th April 2011, 10:21 AM   #5
add is offline add  India
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Default LM 1875

thanks lineup,it worked after removing R3 and R17

both channels were working but the cap " c4 " has a got a bulge and the 12v supply to the ic TL072 is coming around 9.6v but the other
supply -12v is there to the ic

one channel is dead but the other channel is working smoothly and good.


before this also the cap got the bulge and the supply didn't appeared properly to the ic TL072 .
i have checked the supply +21/-21 to LM1875 ic which is fine.
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Old 4th May 2011, 12:01 PM   #6
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Hi add

where do you get those LM1875 chips in india and what price is for each one LM ?????????
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Old 23rd May 2011, 12:02 PM   #7
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Hi add

where do you get those LM1875 chips in india and what price is for each one LM ?????????
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