I'm trying to design a PCB for a couple of op amp working both as amplifiers and filters. Working with signals from DC to 3kHz. Questions are:

1. Is there a recommendation for the vias (like size, maximum length)?
2. Should I place the common GND copper area around the board?

I have been trying with Ultiboard and came up with something like this:

 

http://www.armisteadtechnologies.com/trace.shtml
...to calculate current flow limits and design for ample width on power carrying traces.

If you have noise pick up problems then full board ground planes and additional shielding can be applied to minimize it. Otherwise, a simple sealed metal enclosure is sufficient for shielding purposes and environmental protection.

 

The board design depends on the voltage level of the signal, but for 3khz bandwidth it doesn´t matter how long the traces are etc.

 

I use vias with 1mm holes.

Be very careful with audio to keep the power supply and audio ground in a star configuration. Failure to do so will see power supply hum on the audio.

 

In general, keep the trace lengths to the op amp summing (-) junction as short as possible and keep high level input or output signals far away. Short traces are more important the neatness. The summing junction is very sensitive to stray signal/noise pickup and parasitic capacitance.

 

Be very careful with audio to keep the power supply and audio ground in a star configuration.

What is a star configuration?

About the length of traces: I grouped the components of each op amp near the pins of the IC and then let the program autoroute. I have three ICs (using 5 op amp) a couple of 5x2 connectors within a PCB of 112mm x 90mm (4 2/5 x 3 1/2 inches).

 

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About the length of traces: I grouped the components of each op amp near the pins of the IC and then let the program autoroute. I have three ICs (using 5 op amp) a couple of 5x2 connectors within a PCB of 112mm x 90mm (4 2/5 x 3 1/2 inches).

That's ok if you group the components that go to the summing junction as close to that summing pin as possible.