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Old 20th May 2008, 03:19 AM   #1
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Default Considering a chip amp...

...but I have a couple questions. First of all, what are the rated power output ratings of these three amps:

LM3886


LM3875


LM4780

And second, is there any one particular that stands out, or that I should stay away from? Any opinions on these amps would be useful, and much appreciated. Thanks,

-Justin
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Old 20th May 2008, 05:20 AM   #2
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LM3886 1 x 68 W @ 8 Ohm

LM3875 1 x 56 W @ 8 Ohm

LM4780 2 x 60 W @ 8 Ohm

Datasheets are available from http://www.national.com/apnotes/AudioProducts.html

LM3875 sounds (ever so slightly) warmer, due to (ever so slightly) higher 2nd harmonics, but is not officially produced anymore.

LM4780 is two LM3886 on one chip. Advantages of the LM4780 are better thermal coupling between the channels, more compact layouts possible for stereo, parallel or bridged applications. Disadvantages are lower output power due to higher heat sink requirements (you won't notice the difference under normal listening conditions), worse channel separation, layout requires usually two layer boards, soldering is more difficult, due to very little spacing between the pins.

You won't find significant differences in sound quality or character. The differences you will find, depend rather on the external components and the layout than on the chip model.
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Old 20th May 2008, 07:13 AM   #3
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My input:

lm3886 is only 50 W into 8ohm with +-35V rails (according to datasheet)

and 68W into 4ohm with 28V rails. (according to datasheet)


I would go for the 3886 if you want to drive 4 ohm loads since it has the highest current capability.

In simple terms.

for lm3886

25-0-25 (minimum 160VA for stereo application ) for 8ohm loads

20-0-20 (minimum 160VA for stereo application) for 4ohm loads (18-0-18) might be easier to get )
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Old 20th May 2008, 08:00 AM   #4
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Quote:
Originally posted by pacificblue

LM4780 is two LM3886 on one chip.
As far as I understand it's two LM3886 chips in one package.
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Old 20th May 2008, 08:01 AM   #5
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A possible advantage for the LM3886 is thicker pins in the package but if you plan to buy a pcb this won't matter.
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Old 20th May 2008, 02:23 PM   #6
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Ok so if the amp I'm looking at based on the LM4780 is a dual mono format, that means that it has a separate LM4780 per amplifier board. Does that mean it is utilizing both of it's internal LM3886 chips in a bridge form for more output? Maybe Peter Daniel can chime in as I believe that is his site.

-Justin
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Old 20th May 2008, 05:07 PM   #7
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I'm pretty sure those boards are designed to be easily configurable into paralell, stereo or bridged operation by simply moving a few components.
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Old 21st May 2008, 04:13 AM   #8
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Has anyone any experience building either of these three kits?
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