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francesco81rs 1st June 2012 02:47 PM

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.

pacificblue 1st June 2012 06:07 PM

You can use 1/8 W, if you like.

sgrossklass 1st June 2012 08:03 PM

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.

francesco81rs 4th June 2012 09:03 PM

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:
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!

francesco81rs 8th June 2012 10:03 AM

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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