FINALLY; I have finished my stereo LM3886 board. - diyAudio
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Old 16th January 2007, 08:48 AM   #1
Dxvideo is offline Dxvideo  Turkey
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Default FINALLY; I have finished my stereo LM3886 board.

Hi all,

I am very excited. Finally i finished and tested my amp last evening.
Click the image to open in full size.
As you can see in the schematic, i added some (+7dB) gain on 20Hz-50Hz band. Its for eqalising to my speakers and calculated. I putted no zobel and no input decoupling cap. Also i dont use an input load, potentiometer acts as input load.
This is the PCB layout for stereo circuit;
Click the image to open in full size.
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Old 16th January 2007, 08:56 AM   #2
Dxvideo is offline Dxvideo  Turkey
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Click the image to open in full size.
As you can see at the photo, its very crowded PCB but it works very stable.
I can hear no noise, no hum, no buzz or no switch on pop. In fact i didnot test it with real music and my spk.boxes. But as i tested with my signal injector and little midragnes (10cm) the amp works very clear.
The PSU was my 2x24v 4,5A SMPS and on board i use only 1000u+10u+100n as snubbers.
Click the image to open in full size.
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Old 16th January 2007, 09:00 AM   #3
Dxvideo is offline Dxvideo  Turkey
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I will test it with my iPod and speakers tonite. I will write the results tomorrow.
Special thanks to Mr.Nico RAS from here. He helped (still helping) a lot on that project.
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Old 16th January 2007, 10:42 AM   #4
Dxvideo is offline Dxvideo  Turkey
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And a question as usual;
I want to put it a small box. Never mind the PSU, i will put it in another enclosure.
I have some worries about the heatsink dimensions that i have a huge one like this;
Click the image to open in full size.
Its a 20cm x 10cm and i guess its about 0,7C/W. But i dont want to use it because of the dimensions. I will drive 4ohm speakers and use it for my iPod (50Wx2 max) in my room (not for parties) Under that situations; may i use a pair of socket 478 standard heatsink without fans?
Thanx a lot.
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Old 16th January 2007, 10:48 AM   #5
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Default Small value resistors

The actua; benefit of these is clear, why they help is debated. But try adding some less than one ohm resistors in series with those 100n caps. Connect the cap to ground and the resistor to the rails.
This will make what is known around here as a snubber. I know the theory of parasitic oscilations, but cannot see with my slow scope.
What I hear with these added resistors is a smoother, more even tone. Once I swapped them in and out a couple times it convinced me that just adding a small bypass cap is not always beneficial. But a small bypass and resistor has always been an improvement.

George
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Old 16th January 2007, 10:55 AM   #6
Dxvideo is offline Dxvideo  Turkey
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Hmm interesting.
These under one ohm resistors will help to 100n's for snubbing? Its special for SMPS supplied applications or a general matter? And will these resistors have wattage (4W or more) ? Or 1/4W enough?
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Old 16th January 2007, 02:38 PM   #7
Nordic is offline Nordic  South Africa
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Look for some plumber's flux at the hardware shop... it will make your solder flow nicer...
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Old 16th January 2007, 04:36 PM   #8
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Quote:
Originally posted by Dxvideo
Hmm interesting.
These under one ohm resistors will help to 100n's for snubbing? Its special for SMPS supplied applications or a general matter? And will these resistors have wattage (4W or more) ? Or 1/4W enough?

The 1/4 watt will work. The purpose is dampening the small cap to prevent ringing. I have seen all kinds of graphs and pics showing the benefits.
All my beliefs come from listening. I can hear that it helps give smoother sound.
Try it as is, then add the resistors to see for yourself.
I think the lower wattage will be better for another reason than just availability. The lower wattage are smaller, so should have less inductance. And easier to shoehorn down there under the circuit board.

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Old 16th January 2007, 04:44 PM   #9
CarlosT is offline CarlosT  United States
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I found that some 1/2 watt resistors are too big (too long) to easily fit in the spacing provided in some kit PCBs. Funny enough, the Panasonic carbon film 1/2 watters are smaller than Xicon carbon film 1/4 watters of similar value...go figure

Kudos to Panasonic for making little resistors?
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Old 17th January 2007, 07:04 AM   #10
Dxvideo is offline Dxvideo  Turkey
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Quote:
Originally posted by Nordic
Look for some plumber's flux at the hardware shop... it will make your solder flow nicer...
Plumbers flux! Whats it? A kind of solder?I have never heard it before. In fact its very hard to make a solder path on PCB.

By the way; last night i tested my LM with my iPod and Sony spk boxes from my FH411. (I will do a real spk.box for it this weekend). The sound was very clear and free from distortion or noise. Bass level was very satisfactory because of the Linkwitz equalisation. But the problem was; total output level is about 10W each at full volume as i can mesure (or sense) with my EARS.

Do you think 27dB is not enough (on flat response)? Or iPods headphone output level is not high as needed? Or should i use a preamp, but i will use it for just my iPod and PC...
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