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Old 9th July 2014, 05:22 PM   #1
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Default LM1875 distortion

I have tried this model of LM1875 audio amplifier.. http://www.electronics-lab.com/blog/...-ic-lm1875.jpg .. it makes a huge amount of distortion.... when the input volume is at a lower stage it is cristal clear...bt whenever i increase the volume the sound gets worser..i have used a 8ohm 3W speaker to get the output....more info: 1000uF cap. of 16V electrolitic,100nF 63V cap. of polyester,0.22uF of polyester(marked as 2A104J),1uF electrolitic of 50V,27uF electrolitic of 16V ...i have used 12V 2.5A transformer split voltage...and the most important part is that both the ic and the speaker get so hot...please help me!!!
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Old 9th July 2014, 06:23 PM   #2
adason is offline adason  United States
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did you check the DC on the output?
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Old 9th July 2014, 06:26 PM   #3
blu_glo is offline blu_glo  England
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The circuit values look suspect I'd reduce the 10K feedback resistor R4
to 4K7 as the IC may be oscillating with those suggested values....
You are also on quite a low supply for this chip maybe 18V or more would work better

Last edited by blu_glo; 9th July 2014 at 06:42 PM.
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Old 9th July 2014, 06:56 PM   #4
frank1 is offline frank1  United Kingdom
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Quote:
Originally Posted by flame boy mamun View Post
the ic and the speaker get so hot...please help me!!!
Are you just over-driving your poor 3W loudspeaker?

Frank.
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Old 9th July 2014, 07:40 PM   #5
adason is offline adason  United States
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that's not likely the case...I built nemerous LM1875 amps, they run pretty cool, never too hot, assuming proper heatsink
even if you drive 3 watt speker pretty loud, it should not be too hot, that may indicate DC going through the coil, or the oscillation, as mentioned above
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Old 9th July 2014, 07:47 PM   #6
AndrewT is offline AndrewT  Scotland
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Originally Posted by adason View Post
did you check the DC on the output?
did you check?
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regards Andrew T.
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Old 9th July 2014, 08:46 PM   #7
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yah....i used a heatsink.......i didnt check dc on output,in addition i hvnt heard any noise when the circuit was not in use....

Last edited by flame boy mamun; 9th July 2014 at 09:12 PM.
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Old 9th July 2014, 10:24 PM   #8
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Measure the output offset. That's the first step.
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Old 10th July 2014, 05:17 AM   #9
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i also wanna know that are those polyester capacitors making noise (which are not ceramic)?
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Old 10th July 2014, 08:15 AM   #10
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Yah...i found dc voltage when the amplifier was making distortion...bt when it wasnt making distortion (in lower volume input) i found no dc......i used 47k instead of 10k,distortion decreased,bt gain too
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