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Old 21st April 2011, 05:39 PM   #1
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Default Lm1875 stereo amplifier

i built a stereo amplifier on 2 LM 1875. WHEN I START THE AMPLIFIER IT WORKS ONLY FOR 15 SECONDS NICELY AND THEN SHUTSDOWN, WHEN I SWITCH IT OFF AND SWITCH ON AGAIN IT DOES THE SAME WHAT COULD BE THE PROBLEM
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Old 21st April 2011, 08:33 PM   #2
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Why are you shouting? What is the size of your heatsink? E
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Old 21st April 2011, 08:34 PM   #3
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Heat sinks?

:)ensen.
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Old 21st April 2011, 09:40 PM   #4
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Yea, Bob Pease used old VW cylinder heads. Thermal resistance is supposed to be less than 0.5C/W
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Old 21st April 2011, 09:48 PM   #5
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Hey, that woul make for a great converation piece for the living room! An amp, VW cylinder heads left and right. Better talking about than that sofa you made out of that old whiskey barrel I helped you empty! E
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Old 22nd April 2011, 07:40 PM   #6
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is the problem because of heat sink

Last edited by add; 22nd April 2011 at 07:56 PM.
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Old 22nd April 2011, 08:48 PM   #7
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Quote:
Originally Posted by add View Post
is the problem because of heat sink
It could be there is not enough heatsink to cool down.
There is a protection against overheat.

Otherwise check you have everything put together right.
Normaly LM1875 is easy to get to work.

What is your power supply? VDC?
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Old 25th April 2011, 06:57 PM   #8
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Default LM 1875

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 25th April 2011, 07:31 PM   #9
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It is nothing to do with TL072.

Are both channels doing the same?

I should checkout that the supply rails and ground are correctly attached.
LM1875 should take +/-21 Volt, I think.

Another thing that can switch off the amp is output shortcircuit or too heavy load.
Use one 8 Ohm or 10 Ohm power resistor as dummy load.
Checkout what you have connected to output pins.
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Old 25th April 2011, 07:39 PM   #10
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The pcb lay-out may be such that it causes oscillation. Show us your pcb lay-out and check the output of the amp with an oscilloscope. E
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