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Old 2nd July 2006, 04:24 AM   #11
ir is offline ir  New Zealand
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i use a 3876 power amp driving a 15in sub. works beautifully and runs to VERY high volumes without trouble

fan forced cooling will probably be overkill unless you're using a very small heatsink
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Old 5th July 2006, 05:50 PM   #12
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Just be sure you connect pin 5 correctly for complete compatibility with the LM3886, as noted on the datasheet. The LM2876, LM3876 and LM3886 are all fully drop in replacements as long as pin 5 is connected for the LM3886. Pin 5 is a NC for the others.

All of these amplifiers will drive 4 ohms fine but at reduced output power. Notice the spec. no Output Current Limit in each datasheet, LM2876 = 3A, LM3876 = 4A, LM3886 = 7A. Two things are going to limit output power at 4 ohms, current and heat. For the LM2876 and LM3876 there is not as much output current aviable so output power is going to be lower. This is not a problem with the LM3886. Output power is directly related to die size and the larger the die size the better thermals are in the package so larger die can handle higher power dissipation. If you are planning on driving 4 ohms use the LM3886. If doing 8 ohms either of the others will be fine. National test with sine waves so the recomended voltages and output powers in the tables are pretty much worse case. Running music (although a sub it more demanding) is less stressful than sine waves. Check out the Overture Design Guide National has on there web site here--> http://www.national.com/appinfo/audio/

Gives you some good info on designs. Helpful in determining what you need for voltages, heat sink, etc. Keep in mind that the thermals section is calculated using worst case sine waves. I have run amps higher than they say but only with music.

-SL
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