lm3886 output network with coil or not?

[weiyan]

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]

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]

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]

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

 

[djoffe]

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]

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]

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]

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]

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]

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.

 

[weiyan]

10 Turns of 1mm copper wire around the body of a 1W resistor is easy enough to DIY.

I remember a post in this forum said using pure air coil only. If wrap copper wire around a resistor may risk the saturation of the resistor.

 

[Davey]

I remember a post in this forum said using pure air coil only. If wrap copper wire around a resistor may risk the saturation of the resistor.

No.

The question that should have been asked by now is.....what type of speakers are you going to attach to these amplifiers? The impedance load might make your decision for you.

Generally, you could do without the LR circuit on the output since it's purpose is to decouple capacitive loads. Typical speakers would not cause the amplifier a problem (with that condition.)

The RC Zobel network is useful to terminate the amplifiers into a defined resistance above the audio band. Typical speakers MIGHT cause the amplifier a problem in this instance since they become inductive at high frequencies and would unload the amplifier.

However, it wouldn't hurt to use both networks on the output. A fairly bullet-proof implementation is the PM21 amp from Marchand.

(Take note of the photograph with wire wrapped around the resistor to create the L/R combination.)

PM21 Dual Audio Power Amplifier Module

http://www.marchandelec.com/ftp/pm21man.pdf

Hope that helps.

Dave.

 

[weiyan]

Dave,
Thank you.

I am using an 8ohm full range speaker. Its unlikely to use a film speaker(static electric) in future. Its better to have all safety measures. I think I can modify the circuit with this information.

 

[silver1omo]

Also check:
Single Chip 50W Stereo Amplifier

An externally hosted image should be here but it was not working when we last tested it.

 

[davidsrsb]

High capacitance speaker cables ie parallel tape and cat-5 multiple insulated conductor types, need this inductor

 

[KatieandDad]

I remember a post in this forum said using pure air coil only. If wrap copper wire around a resistor may risk the saturation of the resistor.

Snake oil again.

There is nothing in a 1W Carbon Film resistor to magnetically saturate.