lm3886 output network with coil or not?

weiyan · 28th July 2012, 12:57 AM

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

silver1omo · 28th July 2012, 03:18 AM

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.

weiyan · 28th July 2012, 03:53 AM

Quote:

Originally Posted by silver1omo

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.

silver1omo · 28th July 2012, 03:56 AM

I recommend you to do a search for zobel in the forum and read the opinions.

djoffe · 28th July 2012, 01:44 PM

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.

Update My Dynaco

benb · 29th July 2012, 04:16 AM

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.

weiyan · 29th July 2012, 11:00 AM

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.

weiyan · 29th July 2012, 02:46 PM

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?

KatieandDad · 29th July 2012, 02:51 PM

Quote:

Originally Posted by weiyan

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.

johnr66 · 29th July 2012, 03:05 PM

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.

28th July 2012, 12:57 AM	#1
weiyan diyAudio Member Join Date: Jul 2012 Location: Fanling	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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28th July 2012, 03:18 AM	#2
silver1omo diyAudio Member Join Date: Jan 2011 Location: Mexico	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.

28th July 2012, 03:56 AM	#4
silver1omo diyAudio Member Join Date: Jan 2011 Location: Mexico	I recommend you to do a search for zobel in the forum and read the opinions.

28th July 2012, 01:44 PM	#5
djoffe diyAudio Member Join Date: Oct 2008	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. Update My Dynaco

29th July 2012, 04:16 AM	#6
benb diyAudio Member Join Date: Apr 2010	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.

29th July 2012, 11:00 AM	#7
weiyan diyAudio Member Join Date: Jul 2012 Location: Fanling	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.

29th July 2012, 02:46 PM	#8
weiyan diyAudio Member Join Date: Jul 2012 Location: Fanling	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?

29th July 2012, 03:05 PM	#10
johnr66 diyAudio Member Join Date: Mar 2009	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.