lm3886 electrical noise

eketehe

Member
2007-11-17 3:44 pm
i'm just finish to instaled 2.1 soundsystem in my mom's kitchen.
its dual lm3886 + ETI 150watt ( 4 transistor ) powered by single square 10A transformator 220v/24V - 0 - 24V, 25A diode bridge and 2 x 12.000uf/50V and 2 x 8200uf/50v in paralel, and a pair of 100nf wima MKP/100v at the end.

i built this all to replace my previous DIY project, 2.1 of 2 x lm1875 + 70watt bjt amp which sounds to weak to drive my 2 x 3ways especially the 12" woofer and my 10" subwoofer.

it runs and sounds well, with more detail and kicking on bass, for mid and hight freq i have to say that the previous lm1875 produce a little more natural sound.

i just realized that 1 chanel producing a smooth electrical noise, i thought its from coolcase near of left speakers. sound alike., but when i turn it off/on found yes, it was from my left drivers. so smooth, i find this problem two days after and i don't find this problem before, since test one by one of the three amp before instaling.

i put my suspicions for these points :
- The transformator is to small to supply power for alltogether runs amp, or maybe the capasitor bank? or the square transformator i/o toroids?.
- ETI amp is not match with LM3886 and eats most of all power supply.
- less grounding.. for i put the amp up near the roof.
- kitchen room is not suitable for any soundsystem except mini-compos, and the refregerator operation may infect to a/c in.
- long driver cables, its about 3.5 metres per chanel.

your input would might be kill this noise and solve my problem.
thks
 
Input? Exactly. Is there a load at the amplifier's input, directly before the cable starts its long run? Such could be a potentiometer or resistor (parallel--a load). . . But, is it there?

Is there a 330pF (or so) cap at (parallel) the input to stop radio interference?

Is there a speaker zobel in place, oh say, 4 ohms with 0.15uF, or anything similar?

How long do the DC power lines run before reaching the amplifier boards? If its very long, those boards may need additional capacitiance at the rails.

Are the grounds seperate, such as input, output, and power, once met, never meet again?

Hey, that's all the ideas I have. Kudos for a cool kitchen sound system. ;)
 
How about starting out with and EMI filter just before the transformer....

Also, are you able to move the system into a different room to see if that affects the noise....

You may very well have a bad transformer....I had a bad one at one point...actually it was a cheap one. Once I changed it all was good.
 

eketehe

Member
2007-11-17 3:44 pm
Tks for the kudos, mostly something new for me.

Input? Exactly. Is there a load at the amplifier's input, directly before the cable starts its long run? Such could be a potentiometer or resistor (parallel--a load). . . But, is it there?
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the source is from other box ( plastic ), conected by RCA jack. the source is an analog radio, cd rom, mini jack to play music from mp3 payer / handphone and a three point chanel selector. the signal splited to meet the crossover active for subwoofer and tl074's tone control with defeat mode, yes theres a 50K mono pot and 100K stereo pot. i have check signals with earphones, the out signals from this box is clear.

Is there a 330pF (or so) cap at (parallel) the input to stop radio interference?
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this is new for me, i usualy put 100K ohm in paralel, but for this project i didn't. i will try your idea for 1st action.

Is there a speaker zobel in place, oh say, 4 ohms with 0.15uF, or anything similar?
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Pls kindly adv what is the speaker zobel? how's the usage / install?
fyi, the woofers is in sit floor boxes, but i separate the midrange, hang at 1,7metres height and tweeters at 2,5 metres. the pssive crossover is also outside the speaker's box.

How long do the DC power lines run before reaching the amplifier boards? If its very long, those boards may need additional capacitiance at the rails.
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its about 15cm long, 1 spin 'em together before met the board. there is additional capacitance.

thanks for the precious info :)
 
Thanks for the inputs, and sorry to ask what is EMI filter means?

No problem at all....Electro Magnetic Interference Filter.....essentially it gets rid of the "noise" in the line.

Go here and check some examples out - http://www.filterconcepts.com/ac_filters.html But they can be had just about anywhere...I bought a box of them on GreEdBay for about 5 bucks.

I have no idea as to what type of power you have coming into your house.....but there are several options available.
 
eketehe said:
. . . i usualy put 100K ohm in paralel, but for this project i didn't. i will try your idea for 1st action.
The 100k ohm should work fine. However, 22k is stronger for noise-kill. Since 56k is in-between, maybe try that for the first go? ;)

Another fix for crazy noises is to smear on some flux and re-solder the connections, nice, tight, and shiny. Be sure to touch only with a bright clean soldering iron tip.
I use #0000 fine steel wool to polish the soldering iron tip whenever its any other color than bright silver.
If there's any ceramic caps, hold them with your fingers while soldering, because they can withstand no more heat than your fingers. ;)

Pls kindly adv what is the speaker zobel? how's the usage / install?
fyi, the woofers is in sit floor boxes, but i separate the midrange, hang at 1,7metres height and tweeters at 2,5 metres. the pssive crossover is also outside the speaker's box.
That's an RC network just outside of the highest pitches of the audio band. If you are using a kit, then it may (or may not) already be present.
Onto the amplifier's speaker output terminals can go 4 ohms + 0.1uF, or 4 ohms + 0.22uF.
Cap at the ground terminal, resistor at the hot terminal, like:
- cap resistor +


wboyd said:
No problem at all....Electro Magnetic Interference Filter.....essentially it gets rid of the "noise" in the line.
Go here and check some examples out - http://www.filterconcepts.com/ac_filters.html But they can be had just about anywhere...I bought a box of them on GreEdBay for about 5 bucks.
I have no idea as to what type of power you have coming into your house.....but there are several options available.

What model do you use at your place? It would be so nice to buy something already "proven" to work. ;)
 

eketehe

Member
2007-11-17 3:44 pm
i have open the amp and re-soldering some part, change the RCAs and cables with better, also change the stereo pot with new one since its humming when i touch.

The 100k ohm should work fine. However, 22k is stronger for noise-kill. Since 56k is in-between, maybe try that for the first go?

when i striping the amp, just realized that the 22K ohm,and network said speaker zobel is already fit but in different way, or it is not the said network? pls check the drawing

so sorry to tell that i was buy a PCB than find some good parts without knowing what 'em stands for :D

I don't really know how they works, but happy to tell that the noise is already gone :)
however i found other noise : the refrigerator is humming louder when i turn on the system! aargh thats my mom's authority.
 

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eketehe

Member
2007-11-17 3:44 pm
Dear All,
Thanks for your constribution in advance,
i just leave this project, for they sounds just excelent for my poor ears. also has defeat all my audio system collection ( mostly factory made ) even with sets of more than 35 years old,ex my dad's speakers. except the subwoofer.
I'm willing to have my own room sound system, the best one, to discover a better hearing and up grade my ears.

i'm interest to rebuilt my lm1875, maybe in gainclone, i found in this forum that the chipamps is the superb one, and all part seems available here.

maybe someone,can inform me whatkind of speakers best to fit for this LM1875, i have known that 3way with 12'woofer is too large for 'em.
I found danielwritebac has an LM1875 in madisonears topic. hope you can help,
my friend adv me to have the fostex ( fullrange ) with their box design. fostex is very expensive for my pocket.. but is it the best?
 
eketehe said:
maybe someone,can inform me whatkind of speakers best to fit for this LM1875, i have known that 3way with 12'woofer is too large for 'em.
not always true.
Bigger speakers tend to be more efficient.
Small speakers tend to need more power for the same volume.

A 3way with 12inch bass driver may be an excellent partner to a chipamp.

I had a Richard Allen Pavanne, which had a maximum power handling of around 20W, this is an 8ohm 3way with 12+8+4inch drivers.
 
eketehe said:
. . . I'm willing to have my own room sound system, the best one, to discover a better hearing and up grade my ears.
. . . maybe someone,can inform me whatkind of speakers best to fit for this LM1875, i have known that 3way with 12'woofer is too large for 'em.
. . . my friend adv me to have the fostex ( fullrange ) with their box design. fostex is very expensive for my pocket.. but is it the best?

Speakers for low-power operation:
Tang Band 6-1/2" and a very small tweeter. This makes 92db.
If it isn't enough power handling, you can add high-speed 12" woofers (fast, "nervous," coated/composite paper).

Voltage to push existing speakers:
LM1875 has enough power for the existing speakers. It might not have enough voltage and heatsink.
Mine operate at 28.5vDC rails with large heatsinks. . . and large, inefficient, speakers.
Average SPLs are slightly below 20 watt transistor amplifiers, but dynamics come at far above.

P.S. It would be "unnecessary" (incredibly loud) to combine the two pieces of advice above. ;)

EDIT: See also "wideband" style. Its a form of full-range style, except that there's "helpers" for the highest and lowest pitches, like Harbeth Monitor 40.
 

eketehe

Member
2007-11-17 3:44 pm
AndrewT said:
not always true.
Bigger speakers tend to be more efficient.
Small speakers tend to need more power for the same volume.
-------
Tks andrew,
Yes i'm agree with you, i just proof tht smaller woofer need an extra power.
-------
A 3way with 12inch bass driver may be an excellent partner to a chipamp.
-------

i'm considered to retry this composition, i have 1 set for test :)
maybe some power correction for this amp will much help.
 

eketehe

Member
2007-11-17 3:44 pm
danielwritesbac said:


Speakers for low-power operation:
Tang Band 6-1/2" and a very small tweeter. This makes 92db.
If it isn't enough power handling, you can add high-speed 12" woofers (fast, "nervous," coated/composite paper).
Voltage to push existing speakers:
LM1875 has enough power for the existing speakers. It might not have enough voltage and heatsink.
Mine operate at 28.5vDC rails with large heatsinks. . . and large, inefficient, speakers.
Average SPLs are slightly below 20 watt transistor amplifiers, but dynamics come at far above.

Tks Daniel,
anyway, my just finished amp, was have a little noise again, this time was the ETI for subwoofer, then i put 22K ohm + 330pf in paralel for input. then again the problem is gone :)

my previous Lm1875 was operate at 24.2VDC from 50VAC toroid, with 4 x 4700uf in paralel per rail, is that suficient? the network is as per datasheet schematic.
yes the chips is as hot as irons, i also put an extra heatsink.
I will try to find that high speed 12'
i'm already stisfied with the real sounds in mid and high,especially for vocal, strings and mid-high percussion. i just need more detail for kick bass to meet low freq bass from subwoofer.
the detail i mean, is just like what the lm3886 produced. the good ambience is come when its meet the low sound from subwoofer. i'm using the crossover active to awake the 20hz-100hz freq.
my idea is to combine thats all good sound. thought the 3886 is more flexible, its handle madonna's techno very good.