LM 3886 Tips...

-_nando-_ · 28th December 2005, 01:58 AM

Hi !!

I bought two 3886 to drive four 20W 4Ohms speakers, two for each channel, so, 8Ohms, 40W.

Each 3886 will work with 84 V, and they will be fixed in a BIG heatsink. I'll use HIGH PASS filter to this !

Now, I want to know, before build this, if anyone have some tips and tricks about this 3886 !

Thanksss !!!!!!!

Jay · 28th December 2005, 02:22 AM

No tricks, but with such a high voltage, carefully make a good connection between IC and heatsink. And don't forget, a failure in supply connection will take away your speaker.

-_nando-_ · 28th December 2005, 12:39 PM

Wow

But I"m thinking in use 50v 47uF capacitors between the amp and the speakers. These amps (3886) and speakers are not going to play bass, just mids and high... Bass will be an c200 with 12" 125W subwoofer.

With these capacitors connected between the amp and speakers, will the speakers go away if the supply connection fail?

If the answer is yes or no, doesn't matter, this is not gonna fail

Any crossovers project ?

jackinnj · 28th December 2005, 01:16 PM

the LM3886 is an opamp so (within limits -- it is a high gain, high power device) you can tailor the feedback network to provide the slope you need -- you must use a RC snubber on the output if you are going to use it as an active filter.

you can use Texas Instruments Filter-Pro (freeware) to calculate the filter values -- plug in a gain of 20.

you might be better off just using an opamp buffer, however -- one with a fairly high gain bandwidth product --

AR2 · 28th December 2005, 01:45 PM

It has been a while that I was playing with chip amps but as far as I remember your voltage is too high. When you say 84V - is that between rails, or + 84V and - 84V.
Even between rails is too much, and other combination is leathal.
I would suggest lower voltage - something like 31 - 32 V per rail. max.

-_nando-_ · 28th December 2005, 08:30 PM

84v total, it's 42+42v.

I don't have other transformer, and I'll cut the low frequency, so I don't think the 3886 will stress so much heh !

Jay · 29th December 2005, 12:50 AM

Quote:

Originally posted by -_nando-_
But I"m thinking in use 50v 47uF capacitors between the amp and the speakers. These amps (3886) and speakers are not going to play bass, just mids and high... Bass will be an c200 with 12" 125W subwoofer.

With these capacitors connected between the amp and speakers, will the speakers go away if the supply connection fail?

With polar cap, I guess it depends on which side of the rails that fail. I have tried many exotic output caps on the output, and they affect the sound quality. Worse to be precise. But my Nippon-Chemicons is okay. It seems that old (burned-in) caps work better

-_nando-_ · 29th December 2005, 01:39 AM

Okay, so what should I do to cut off the BASS without degrading voice and etc? I just don't want 200Hz and upper frequencies...

I tryed 47uF caps, but the voice and others mids were VERY degraded...

Any crossovers? Can be a passive one too...

digi01 · 29th December 2005, 02:06 AM

IMHO,3886 at 84VDC is very dangerous!under 70V is better.

good luck
Zang

neutron7 · 29th December 2005, 02:41 AM

how long has the 3886 been made? much longer than any cpu. they probably have made new chips on different process, and still keep old PDF for everyone.

i wouldnt be suprised if you could run 50v a rail and no trouble at all as long as it doesnt oscllate.

they are cheap, very mature and probably with a HUGE margin of error.

28th December 2005, 01:58 AM	#1
-_nando-_ diyAudio Member Join Date: Dec 2005 Location: Sao Paulo	LM 3886 Tips... Hi !! I bought two 3886 to drive four 20W 4Ohms speakers, two for each channel, so, 8Ohms, 40W. Each 3886 will work with 84 V, and they will be fixed in a BIG heatsink. I'll use HIGH PASS filter to this ! Now, I want to know, before build this, if anyone have some tips and tricks about this 3886 ! Thanksss !!!!!!!

29th December 2005, 02:06 AM	#9
digi01 diyAudio Member Join Date: Mar 2003 Location: BEIJING	IMHO,3886 at 84VDC is very dangerous!under 70V is better. good luck Zang __________________ 2010 DIY ALBUM UPDATED UCPv1(preamp) & DUAL(power supply)

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28th December 2005, 02:22 AM	#2
Jay diyAudio Member Join Date: Feb 2003 Location: Jakarta	No tricks, but with such a high voltage, carefully make a good connection between IC and heatsink. And don't forget, a failure in supply connection will take away your speaker.

28th December 2005, 12:39 PM	#3
-_nando-_ diyAudio Member Join Date: Dec 2005 Location: Sao Paulo	Wow But I"m thinking in use 50v 47uF capacitors between the amp and the speakers. These amps (3886) and speakers are not going to play bass, just mids and high... Bass will be an c200 with 12" 125W subwoofer. With these capacitors connected between the amp and speakers, will the speakers go away if the supply connection fail? If the answer is yes or no, doesn't matter, this is not gonna fail Any crossovers project ?

28th December 2005, 01:16 PM	#4
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	the LM3886 is an opamp so (within limits -- it is a high gain, high power device) you can tailor the feedback network to provide the slope you need -- you must use a RC snubber on the output if you are going to use it as an active filter. you can use Texas Instruments Filter-Pro (freeware) to calculate the filter values -- plug in a gain of 20. you might be better off just using an opamp buffer, however -- one with a fairly high gain bandwidth product --

28th December 2005, 01:45 PM	#5
AR2 Master Burner Join Date: Dec 2002 Location: San Francisco, California	It has been a while that I was playing with chip amps but as far as I remember your voltage is too high. When you say 84V - is that between rails, or + 84V and - 84V. Even between rails is too much, and other combination is leathal. I would suggest lower voltage - something like 31 - 32 V per rail. max.

28th December 2005, 08:30 PM	#6
-_nando-_ diyAudio Member Join Date: Dec 2005 Location: Sao Paulo	84v total, it's 42+42v. I don't have other transformer, and I'll cut the low frequency, so I don't think the 3886 will stress so much heh !

29th December 2005, 01:39 AM	#8
-_nando-_ diyAudio Member Join Date: Dec 2005 Location: Sao Paulo	Okay, so what should I do to cut off the BASS without degrading voice and etc? I just don't want 200Hz and upper frequencies... I tryed 47uF caps, but the voice and others mids were VERY degraded... Any crossovers? Can be a passive one too...

29th December 2005, 02:41 AM	#10
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	how long has the 3886 been made? much longer than any cpu. they probably have made new chips on different process, and still keep old PDF for everyone. i wouldnt be suprised if you could run 50v a rail and no trouble at all as long as it doesnt oscllate. they are cheap, very mature and probably with a HUGE margin of error.

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