Audio signal through a trace or a solid plane. - diyAudio
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Old 26th February 2014, 10:12 AM   #1
2wice is offline 2wice  South Africa
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Default Audio signal through a trace or a solid plane.

Hi All

I'm designing something where the audio signal can go through either a copper trace on PCB or a solid plate of copper (easier) 32mm*32mm*1mm.

Would there be any negative outcome to using the solid copper plate as signal in/out and ground path?

Kind regards
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Old 26th February 2014, 07:36 PM   #2
DF96 is offline DF96  England
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It depends on what you are connecting to it. For RF a copper plane makes a good ground because it has low inductance. Audio doesn't really care about inductance but it does notice resistance - you need to know where the ground currents are going. That is why audio usually uses star or bus grounds.
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Old 27th February 2014, 04:18 AM   #3
2wice is offline 2wice  South Africa
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Thanks DF96

I can then assume that I can do the following as nothing will be affecting the signal negatively?

Click the image to open in full size.
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Old 27th February 2014, 12:06 PM   #4
DF96 is offline DF96  England
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I don't understand the picture.
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Old 27th February 2014, 12:11 PM   #5
PMA is offline PMA  Europe
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Capacitance??
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Pavel Macura
http://web.telecom.cz/macura/audiopage.html
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Old 27th February 2014, 12:12 PM   #6
2wice is offline 2wice  South Africa
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It's part of a balanced ladder type attenuator.

Here is the final design.Click the image to open in full size.
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Old 27th February 2014, 12:23 PM   #7
marce is offline marce  United Kingdom
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Quote:
Originally Posted by DF96 View Post
It depends on what you are connecting to it. For RF a copper plane makes a good ground because it has low inductance. Audio doesn't really care about inductance but it does notice resistance - you need to know where the ground currents are going. That is why audio usually uses star or bus grounds.
Not all audio (mainly DIY), most professional audio and other audio (comms etc) has ground planes and ALL sensitive analogue PCBs (in fact all analogue)are multi layer with ground planes. The star refers to a star point where a signal ground is joined to a power ground. in fact it is only on here and other such sites that I see the spiders legs style grounds, everywhere else it is generally a ground plane (except the cheapest of the cheap designs).
And in todays RF rich environment a ground plane is your friend.

0.3mm (0.012") trace (standard for DIY and basic designs)
2 layer with ground:
Lo 6.8nH/cm
Co 0.46pF/cm

4 layer with ground:
Lo 4.7nH/cm
Co 0.66pF/cm

Last edited by marce; 27th February 2014 at 12:40 PM. Reason: capacitance figures
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Old 27th February 2014, 01:29 PM   #8
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As already mentioned there will be capacitance between the planes. Also the signal-in plane and signal-out plane are close together and not shielded by a ground plane so there will be some capacitive coupling between them. Signal traces (instead of signal planes) will obviously have very much less capacitance, especially if they follow different paths and only cross ocasionally. For low value resistances in the attenuator the capacitance will probably not matter.
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Old 27th February 2014, 03:31 PM   #9
2wice is offline 2wice  South Africa
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Excellent, thank you very much. I'll try and build it.
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