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Old 19th September 2009, 06:55 PM   #1
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Default LM3886 components

I'm planning to air-wire several LM3886 chips, but the typical application schematic shown on the current datasheet differs from the one that's shown in chipamp.com's assembly manual for their LM3886 kit. Which one should I get components for?

http://www.national.com/ds/LM/LM3886.pdf

http://www.chipamp.com/docs/lm3886-manual.pdf
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Old 19th September 2009, 07:01 PM   #2
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This one revision B.
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Old 19th September 2009, 07:12 PM   #3
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Much appreciated.
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Old 20th September 2009, 01:43 PM   #4
AndrewT is offline AndrewT  Scotland
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fig2 revB needs RF attenuation added.
C2 (22uF) is far too small.
C2>=1.4 * C1 * R1 / R4
>=1.4 * 3.3u * 22k / 1k >=102uF
Try 100uF or preferably 150uF.
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Old 20th September 2009, 03:44 PM   #5
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Quote:
Originally Posted by AndrewT View Post
C2 (22uF) is far too small.
It's the value National recommends. How much difference do you think it makes?

Quote:
Originally Posted by AndrewT View Post
fig2 revB needs RF attenuation added.
And the ones from National and Chipamp don't?
I'm not saying it's a bad idea (rather, a good one) but I haven't seen it on any LM3886 schematic.
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Old 20th September 2009, 07:00 PM   #6
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Quote:
Originally Posted by MJL21193 View Post
And the ones from National and Chipamp don't?
I'm not saying it's a bad idea (rather, a good one) but I haven't seen it on any LM3886 schematic.
Actually it's on almost every National schematic as Cc. Did you check the "optional" external components description?

In addition, C2 creates a roll-off at a certain frequency. You can customize this frequency to have less effect on the audio by changing the value. The optional external components description gives the formula.
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Last edited by Redshift187; 20th September 2009 at 07:05 PM.
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Old 20th September 2009, 09:43 PM   #7
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Quote:
Originally Posted by Redshift187 View Post
Did you check the "optional" external components description?
Yeah, no, I didn't look that far down...my laziness showing up (again).

Still, I have built many without the RF protection and I have used 22uF for the feedback cap. I don't think it would make an audible difference with regards to the feedback cap value, as long as it isn't too low.

This are minor issues (non existent IMO) and it seemed that Andrew wanted to nit-pick.
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