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Bridging LM1875 into 4Ohms design with Forced fan Cooling ... Possible??
Bridging LM1875 into 4Ohms design with Forced fan Cooling ... Possible??
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Old 3rd June 2013, 03:24 PM   #1
dannyjmf is offline dannyjmf  Saudi Arabia
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Default Bridging LM1875 into 4Ohms design with Forced fan Cooling ... Possible??

Need help here ... i am helping a friend of mine to design an LM1875 Bridged amp X4 ... which means will use total of 8 LM1875's ... my friend wanted to use this amp for 4ohms speaker (bridged configuration) ... and the design will use force fan cooling total of 8 cooling Fans ... (4 blowing and 4 exhaust) ... will this able to handle 4 ohm in bridge mode?

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Old 3rd June 2013, 03:42 PM   #2
abraxalito is offline abraxalito  United Kingdom
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Getting four paralleled amps stable isn't an easy job - why this approach? Why not a single LM3886 (for example)? What's the power requirement and are the fans being used instead of heatsinks?
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Old 3rd June 2013, 03:51 PM   #3
dannyjmf is offline dannyjmf  Saudi Arabia
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Btw is not a paralled but a bridged LM1875 ... i cant Find LM3886 in my place ... so this is the alternative ... my friend say he dont mind having a very large heatsink for this amp as we used cooling fan to cool the heatsink as much as possible

Anyway i have a 4channel LM1875 DIY ... tried to bridged them into 8ohms with no problems at all ... i wonder if it is 4ohms the IC will run into thermal protection if it overheats ... as if i am not mistaken these IC's have thermal cut off ...

Last edited by dannyjmf; 3rd June 2013 at 03:54 PM. Reason: extra notes
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Old 3rd June 2013, 04:03 PM   #4
abraxalito is offline abraxalito  United Kingdom
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Ah, I see - apologies for my misunderstanding. So there are 4 channels - well the 1875s will 'see' a 2R load when bridged which they won't take too kindly to. Whether it thermally overheats will depend mainly on the supply voltages, then on the music you play and probably after that, on the heatsinking. Certainly you'll get worse distortion with 2R load but whether it will be audible is debatable.
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Old 3rd June 2013, 04:28 PM   #5
dannyjmf is offline dannyjmf  Saudi Arabia
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well ... since this project is confirmed to be build soon ... i will let u know later ....
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Old 3rd June 2013, 07:45 PM   #6
Bone is offline Bone  United Kingdom
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A parallel bridge may work. This would work into 4 ohms. Also uses 4 1875s could give you about 100w
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Old 5th June 2013, 01:00 PM   #7
JMFahey is offline JMFahey  Argentina
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Once you get into that level of complexity, chipamps lose attractive, I'd go discrete .
Plus they limit you a lot, specially on PSU voltage.
Once you start *needing* to bridge + parallel them to meet a power output goal, in my book it means you are going way beyond what was originally expected from them.
Just saying.
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Old 6th June 2013, 06:13 PM   #8
blu_glo is offline blu_glo  England
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I second that, JMFahey, is less complicated to go discrete. Theres only one chip that really lends itself to 4 ohm bridging - the aforementioned LM3886 - would still limit around 120W.....
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Old 7th June 2013, 03:06 AM   #9
martin martinez is offline martin martinez  Mexico
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Excuse my intromision, but what about the parallel TDA 7293 ?
I{m just about finishing one to use it with a 4 ohm load.
Would it be a better solution, or not?
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Old 7th June 2013, 03:59 AM   #10
abraxalito is offline abraxalito  United Kingdom
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Yes, TDA7293 is the easiest solution for a bridged chipamp into 4ohms. With 4 chips you'll be looking at a maximum power over 200W.
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