2 lm3886 for 120w in 4ohm load

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audioloud

Member
Joined 2004
hhiiiiiiii
i m looking for building a 120w power amp in 4 ohm load
this for a sub.
i plan to use 2 lm3886 in the bridged _parallel configguration
but i have one problem.
i don't handerstand how conect it to the speaker. circuit designs on the net contradict themself :
some conect one pin of the speaker to the output of the amp and the second to the ground.
And others conect each pin of the speaker to each output of the 2 chips.
and here im lost. does everyone could explain me the good way to act in that case..:) :)
 
C

carlmart

Member
Joined 2001
preciseaudio.com
audioloud said:
hhiiiiiiii
i m looking for building a 120w power amp in 4 ohm load
this for a sub.
i plan to use 2 lm3886 in the bridged _parallel configguration
but i have one problem.
i don't handerstand how conect it to the speaker. circuit designs on the net contradict themself :
some conect one pin of the speaker to the output of the amp and the second to the ground.
And others conect each pin of the speaker to each output of the 2 chips.
and here im lost. does everyone could explain me the good way to act in that case..:) :)
Click to expand...

A bridged amp's output are ALWAYS the output of each amp, the one fed with the non-inverted input goes the speaker's positive and the one fed from the inverted output goes to the speaker's negative end.

If you wire a speaker between one of the amp's outputs and ground you are just using a single amp, not the bridge. If you wire different speakers to each amp you will be feeding out of phase signals to them and cause a quite strange sound effect. nulling most of the sound if they are close by.


Carlos
 
O

officeboy

Member
Joined 2003
home.comcast.net/~0fficeboy/
I think the confusion here is the difference between bridged and paralleled, if you build a bridged parallel LM3886 you need a minimum of 4 chips.

For a pair of parallel chips, you would basically just tie the outputs of to identical chips together and it would allow you to double the currant (good for a low resistance load like you have)

For bridged chips you tie the non-inverting output of one chip and the inverting output of another chip to each lead on a speaker. This gives you a higher potential for voltage and is better for a high resistance speaker (not good for your 4ohm unit)

For a 2 chip-amp amp I would suggest a parallel connection

You might also want to review AN-1192.pdf from National if you haven’t already
 
mrlots2do

mrlots2do

Member
Joined 2004
officeboy said:
I think the confusion here is the difference between bridged and paralleled, if you build a bridged parallel LM3886 you need a minimum of 4 chips.

For a pair of parallel chips, you would basically just tie the outputs of to identical chips together and it would allow you to double the currant (good for a low resistance load like you have)

For bridged chips you tie the non-inverting output of one chip and the inverting output of another chip to each lead on a speaker. This gives you a higher potential for voltage and is better for a high resistance speaker (not good for your 4ohm unit)

For a 2 chip-amp amp I would suggest a parallel connection

You might also want to review AN-1192.pdf from National if you haven’t already
Click to expand...

Are bridged amp chips a better application than if paralleled.

I'm thinking yes because the non-inverted chip drives cone outward and inverted chip drives cone inward. Doing so, wouldn't the sound be more crisp (short and exact)?

Is my thinking correct here. Two parallel chips (LM3875) would handle 132 watts@8ohms. Two bridged chips (LM3875) would still handle 68 watts@8ohms.

How is bridged/parallel chips better application? Four bridged/paralleled chips (LM3875) would handle 132 watts@8ohms or ??? watts@4ohms. What else? My interest here is using best application for a WtmW with active crossover

Thanks
 
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