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Old 22nd August 2007, 04:24 PM   #11
banana is offline banana  Hong Kong
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Quote:
Originally posted by aparatusonitus


Could you elaborate a bit and explain how one can address this problem?
Suggestions from Opamp app note work well. Rub off ground plane right below output pin, as well as inverting input pin.
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Old 22nd August 2007, 04:42 PM   #12
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Thank you for the tip banana, I like it 'cos it's so easy to implement
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Old 22nd August 2007, 10:05 PM   #13
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Usually, if a circuit is extremely complex, just using a ground plane won't help. It may make the thing even harder to lay out, or you end up with a spidery little bunch of ground plane around all the traces- essentially a randomly wired ground system, rather than a planned one. What is typically done is to go to a 4-layer board. That way you can have your power and ground planes, plus two layers for horizontal and vertical traces. IMO, not really optimal for audio if done in the traditional digital fashion. Good analog design has its own set of requirements unlike just about anything else. The usual way to take care of parasitic capacitance, say around a high value feedback resistor, is to simply void the ground plane underneath the part. Leave a rectangular hole just a bit larger than the part.
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Old 22nd August 2007, 10:14 PM   #14
AndrewT is offline AndrewT  Scotland
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Hi,
reading between the lines of this and previous threads on ground planes, I have come to the conclusion that it takes more skill to successfully implement a ground plane than to work without one.

Or put it another way.
If you have to ask, then you don't have the skill to find and eliminate the problems likely to arise as a result of using a badly designed ground plane.
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Old 22nd August 2007, 10:18 PM   #15
suzyj is offline suzyj  Australia-Aboriginal
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A ground plane is really only useful if you're doing controlled impedance work, and that's not gonna happen at audio frequencies.

That said, copper pours are very useful, as they're the lowest impedance way to rout a given net. Same goes with double sided boards - they give you much more opportunity to do a decent low impedance connection, that doesn't snake all over the board. They also allow you to put components on both sides of the board, making the board more compact, again with commensurate gains in connection impedance.
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Old 22nd August 2007, 10:28 PM   #16
jaycee is offline jaycee  United Kingdom
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All this makes me wonder if I screwed up my latest pcb by adding a ground plane ! It is single sided, but the ground plane was the easiest way to take care of routing the audio ground:

http://www.darkmatter.myby.co.uk/preamp-brd.pdf

and the schematic for those interested

http://www.darkmatter.myby.co.uk/preamp-sch.pdf

The pot is a 100K linear track motorised ALPS potentiometer I salvaged from a mid-80's Pioneer stereo system that the neighbours had thrown away. I plan to use NE5532 for the opamps.

Did I use the ground plane in a Bad Way? I'm still learning how to lay out PCB's well!
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Old 23rd August 2007, 01:10 AM   #17
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Hi jaycee

I have done similar in my recent layouts. Try to place all traces on top and a solid ground bottom.

Apart from stray cap, can a ground plane provide protection against interference?

Shall we add a ground (return path) under a high current trace to cancel the generated magnetic field?

panson
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Old 23rd August 2007, 02:38 AM   #18
sam9 is offline sam9  United States
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It is probably well to distinguish "power ground" (the one that cap caps between it and the rails) from "signal return ground" (the one that also can act as a shield to the signal input). In the case of the first, I try to keep it as short as possible taking up little space on the PCB, the leading it away 90 deg from the PCB as quickly as possible and keeping it away from the input signal, etc. I do similarly with the power rails as much as possible.

The quiet ground may have to wander around the PCB. If you limit it so it doesn't get into the output section where there are higher currents, making it copper fill might be OK. (I didn't find it made a noticiible difference but maybe I'm just an insensitive lout.)
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Old 23rd August 2007, 03:34 AM   #19
banana is offline banana  Hong Kong
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Quote:
Originally posted by panson_hk
Apart from stray cap, can a ground plane provide protection against interference?

Shall we add a ground (return path) under a high current trace to cancel the generated magnetic field?
In practice, it's only a partial shield, and the stray field in audio frequency is only very short range.

It does help reduce crosstalk between adjacent trace after all.
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Old 23rd August 2007, 03:06 PM   #20
h_a is offline h_a  Europe
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What about hatched groundplanes?

Some designers prefer to use these, are these a handy tradeoff in the sense that they do considerably more good than harm? At least stray capacitance is strongly reduced.

What do you think?

All the best, Hannes
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