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Old 28th July 2012, 01:57 AM   #1
weiyan is offline weiyan  Hong Kong
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Question lm3886 output network with coil or not?

I am reviewing which LM3886 kit / assembled unit to buy. There is confusion on the output design.

In the datasheet's test circuit's output network has a 0.7uH coil parallel with 10Ohm resistor.

I go through LM3886 boards, only a few have this network. Most boards doesn't have the coil.

Is the coil and required? And the effect on audio quality?

Thanks.

http://www.ti.com/lit/ds/symlink/lm3886.pdf
Page 5
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Old 28th July 2012, 04:18 AM   #2
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That would be a zobel network and helps to "present" a resistive load to the amp helping avoid oscillation. Required? Depends on who you ask, but I think it is desirable.
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Old 28th July 2012, 04:53 AM   #3
weiyan is offline weiyan  Hong Kong
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Originally Posted by silver1omo View Post
That would be a zobel network and helps to "present" a resistive load to the amp helping avoid oscillation. Required? Depends on who you ask, but I think it is desirable.
Thak you.
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Old 28th July 2012, 04:56 AM   #4
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I recommend you to do a search for zobel in the forum and read the opinions.
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Old 28th July 2012, 02:44 PM   #5
djoffe is offline djoffe  United States
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Going "naked" without the coil/resistor combo is like playing Russian Roulette if it's a general purpose amplifier that could be connected to any speakers with any type of speaker wire. If you have a specific, short speaker wire, and a known speaker, then you could probably skate by without it after you did some stability testing.

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Old 29th July 2012, 05:16 AM   #6
benb is offline benb  United States
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The parts are cheap enough, just add them. Under normal circumstances, they make no difference in sound. Under abnormal circumstances they can make the difference between everything working okay and a burned out chipamp and/or blown speaker.
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Old 29th July 2012, 12:00 PM   #7
weiyan is offline weiyan  Hong Kong
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Thank you for the great replies.

I think its better to buy a board with the coil/resistor combo. Its not easy to buy copper wire to diy this combo.

Thank you.
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Old 29th July 2012, 03:46 PM   #8
weiyan is offline weiyan  Hong Kong
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PA100 DIY 2x LM3886 in parallel gainclone audio amplifier
I found this circuit.

There is no coil/resistor network. Instead, a 2Ohm resistor in series with 0.1uF capacitor, from output to ground. Is this also zobel network?
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Old 29th July 2012, 03:51 PM   #9
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Quote:
Originally Posted by weiyan View Post
Thank you for the great replies.

I think its better to buy a board with the coil/resistor combo. Its not easy to buy copper wire to diy this combo.

Thank you.
10 Turns of 1mm copper wire around the body of a 1W resistor is easy enough to DIY.
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Old 29th July 2012, 04:05 PM   #10
johnr66 is offline johnr66  United States
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I'd recommend the R||L with long speaker wire runs especially if you're pushing the chip using the highest recommended supply voltage. It is not a big deal to make a coil from some enamel wire. You should always have the RC network as well.
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