Check my layout pls. for proper grounding (6 channel opamp pre) - diyAudio
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Old 17th February 2008, 04:02 PM   #1
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Question Check my layout pls. for proper grounding (6 channel opamp pre)

Please have a look at the grounding in my first attempt ever to make a proper layout. Its ment for a 6 channel pre with LM4562 dual opamps and has 2 stages (buffer to the left, gain to the right). The space between the stages is for a 6 channel stepped attenuator fitted directly on the board. Power connector is on the outer left, ground traces are marked in purple.

Is the ground duct alright that way? Thank you for your comments!

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Old 17th February 2008, 04:57 PM   #2
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Where are the attenuators grounded?
Or is the output stage inverting so they dont need ground?
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Old 17th February 2008, 05:04 PM   #3
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The attenuators are grounded on the ground duct too, just between the OUT and IN pads in the middle. I just forgot to show those pads. Both stages are non-inverting.
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Old 17th February 2008, 05:08 PM   #4
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I think that especially that one should be separate from the opamp decoupling.

Try having a separate trace to the PS for the decoupling, and a second one common for the signal, in a star-like fashion.

High-current ones like power supplies and output ground (in power amps) need to be separated from the low current ones, like signal reference traces.
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Old 17th February 2008, 05:25 PM   #5
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You mean that both ground lines are to be completely separated?
That would not work because the signal would be separated from the opamp too ...
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Old 17th February 2008, 05:30 PM   #6
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Not completely separated, but separated all the way from power supply connection.
Like you have one ground duct that connects all the PS decoupling caps, and a second one that connects all the audio grounds.
Then you connect these two near the ground pin on the upper-left side.
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Old 17th February 2008, 05:38 PM   #7
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That makes sense, thank you. I will alter my layout accordingly.

Apart from that, whats about the layout to be found in the "LM4562 (dual op-amp) simple preamplifier" thread:

Schematic:
http://unisonus.com/pdf/DIY/LM4562_schematic.pdf

PCB top layer (description):
http://unisonus.com/pdf/DIY/LM4562_PCB_top.pdf

PCB bottom layer (tracks):
http://unisonus.com/pdf/DIY/LM4562_PCB_bottom.pdf

The grounding there is directly connected to the psu ...
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Old 17th February 2008, 06:47 PM   #8
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Do I have to think of the signal star ground that any (on input as well as on output) connection has to have a seperate trace to the star point? Or does it do when the ground connections of the respective opamp are going to one point and the latter to the common star point?
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Old 17th February 2008, 08:23 PM   #9
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Star ground in theory really means that all connections are meeting at one physical point, but that is nearly never done completely.

I think that the general practice is to do it as often as possible, but for more complex circuits you would probably have to use 3 or more layers to achieve it.

The problem is that when you use more star ground-like connections you have better chance of perfect function and no noise, but you cant really tell how the circuit will perform with standard ground like in the LM4562 preamp you posted.
You just have to try the design by building it and seeing/listening what it does. Then you can cut&re-wire the traces to see if it helps
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Old 17th February 2008, 08:35 PM   #10
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Quote:
You just have to try the design by building it and seeing/listening what it does. Then you can cut&re-wire the traces to see if it helps
Thats the hardest way ...

Would separate groundplanes for power and signal be a better solution?
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