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Old 6th October 2008, 01:42 PM   #1
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Smile Olle:s first chipamp with LM3886! Board layout?

I have found some components at the local junk yard lately
This is how it looks:

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Yes, I am building a gainclone with the LM3886
Mabye a little oversized heatsink and power transformers for a normal two channel gainclone
The powersupply was finnished last week...
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Old 6th October 2008, 01:55 PM   #2
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Default Need pcb-layout!

I recently became a member of a electronic-association for students, so now I can make my own pcb:s That's cool!

I want to build a "normal gainclone", like BrianGT:s pcbs... But I want to make the pcb myself, it's more fun!

I'm looking for a board-layout: Non-inverted, single-sided for LM3886.

There are hundreds of layouts out there, some are made by newbies, and some by experienced people.
Of course I have searched, but its hard for me do decide a good layout.

I found a a layout made by "bigparsnip" here at the forum.
It is non inverted right? There are no errors right?
Shall I use it for my pcb:s?

What do you think?
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Old 6th October 2008, 02:50 PM   #3
AndrewT is online now AndrewT  Scotland
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Hi,
there is no RF attenuation nor chip decoupling on the PCB, nor DC blocking cap on the input.
The decoupling can easily be added directly to the chip power pins on the back of the PCB.
Similarly the RF cap can be paralleled with the Zin resistor on the back.

I don't like the common signal ground with the chip ground.
Similarly the Power Ground is commoned with the Signal Ground.

Either, select a layout with some or all of these features designed into the layout or be prepared to experiment with add ons after you have listened/measured the performance.
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Old 6th October 2008, 03:38 PM   #4
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Quote:
there is no RF attenuation nor chip decoupling on the PCB, nor DC blocking cap on the input.
The decoupling can easily be added directly to the chip power pins on the back of the PCB.
Similarly the RF cap can be paralleled with the Zin resistor on the back.
Okay, these things can easily be fixed, but not the other ones you mension...

Is there a better layout out there?
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Old 9th October 2008, 01:59 PM   #5
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Here's my first eagle PCB layout.
You can use free version of eagle.
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File Type: zip lm3886-eagle.zip (24.5 KB, 250 views)
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Old 10th October 2008, 11:05 AM   #6
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Thank you! But there are things I don't understand...
There are both two inputs and outputs, Why? The LM3886 is inly one channel...

Edit: Now I get it Found the schematic in eagle!
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Old 11th October 2008, 03:33 AM   #7
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This is the first attempt at PCB design and I am still figuring out eagle.
FYI, I made the board using toner transfer, but yet to build the amp.
So I cannot vouch for hum, ground loops etc.

Use at your own risk.

I tried to read and follow the info in previous posts on this forum when
doing the layout.
Feedback resistor is as close as possible to the chip.
The decoupling caps are as close as possible to the chip.
The power lines are on one side, closest to the chip.
The input signal is away from the power traces.
All traces are as thick as I could make them.
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File Type: jpg lm3886-brd.jpg (53.7 KB, 1389 views)
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Old 11th October 2008, 08:31 AM   #8
AndrewT is online now AndrewT  Scotland
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DC coupled amplifier.
Where is the DC detect and output isolation?
No RF attenuation.
The decoupling caps are far too bulky and as a result had to be located too far from the power pins.
Look for 0.1inch or 0.2inch pin pitch for the 100nF decoupling.
NFB tied into the Power Ground instead of the Signal Ground.
Signal Ground sharing trace impedance with Power Ground.
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Old 11th October 2008, 10:53 AM   #9
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I think I have found a good one now!
Single sided non inverting LM3886 PCB

There is a small error, but it seems it's easy to correct in paint
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Old 11th October 2008, 11:42 AM   #10
ratza is offline ratza  Romania
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You can use my design, if you think it's appropriate for you.
http://www.diyaudio.com/forums/showt...26#post1570826
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