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Old 1st June 2012, 01:47 PM   #1
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Default LM3886 input resistence power

Hello everyone, my name is Francesco and is the first time that I write on this forum.
Sorry for my bad English!!!
I wanted to ask a little help...
For a lm3386, what is the right power for the input resistance and the resistance of feedback?
Can I use 1/8W, or is it better to stay on 1/4W?
Thanks to all.
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Old 1st June 2012, 05:07 PM   #2
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You can use 1/8 W, if you like.
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Old 1st June 2012, 07:03 PM   #3
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But avoid thick-film types if you're after lowest distortion. (Since you're asking about 1/8 W, I'm assuming we're talking surface mount parts.)

Referring to Figure 1 in the LM3886 datasheet:
1/8 W is perfectly fine for RB and Ri. You may want to go 1/4 W for Rf1, which sees the highest voltage swing and power dissipation of them all by far.
All of them should be preferably metal film (through-hole) or thin-film (SMD).

For lowest low-frequency distortion, capacitor Ci should be either a bipolar type or about 3 times as large as specified in the datasheet, though I don't think it should be all that important given that the IC has thermal feedback to contend with that increases low-frequency distortion anyway.
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Old 4th June 2012, 08:03 PM   #4
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Thank you very much for your reply.
I was doing the shopping list for components to build a 2-channel with the LM3886 in parallel - bridge configuration and i will use 2 board for each channel with 3 LM3886 in parallel and put in a bridge by a Lundahl input transformer.
The circuit diagram is as follows:
www.shine7.com/audio/bpa300.htm
The only difference I see in the pcb I bought is the 8pF capacitor in parallel with the feedback resistor is printed as 47pF.
Any suggestion about electrical circuit or the type or brand of components is welcome!
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Old 8th June 2012, 09:03 AM   #5
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I found the solution to the question of the capacitor onto another discussion...
I think the capacitor is smaller for not limiting the bandwidth at high frequencies.
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