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Old 3rd April 2011, 08:24 PM   #1
miallen is offline miallen  United States
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Default Organizing Components for Low Noise?

Hello,

I understand that placing high-level low impedance signals next to low-level high impedance inputs can cause noise. But what are the general rules about component placement for minimizing noise?

The following is an example circuit which is supposed to be the input / output buffers of a parametric eq. Here the schematic:

Click the image to open in full size.

and a corresponding layout:

Click the image to open in full size.

Can someone explain how the components of this circuit might be moved to better reduce noise?

Thanks,
Mike
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Old 4th April 2011, 09:47 AM   #2
DF96 is offline DF96  England
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Placing outputs near inputs can create crosstalk or instability, not noise. Noise comes from the components themselves: thermal noise, shot noise, flicker noise.
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Old 4th April 2011, 10:41 AM   #3
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I strongly recommend separating the signal ground from the power supply ground, that will minimize the possibility of inducing power supply noise in the signal lines. I do this in everything I build.
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Old 4th April 2011, 11:17 AM   #4
Mooly is offline Mooly  United Kingdom
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R2 and R4 are not needed.
The ultimate level of noise depends on the component values used and particularly the opamps. At low circuit impedances a bipolar device such as the LM4562 will be quieter... but it's all a matter of degree, and tbh noise (hiss) is often the least of the problems. As others have said, pay attention to grounding.

This circuit as it stands isn't suitable for swapping the FET opamp for bipolar.
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Old 5th April 2011, 12:40 AM   #5
miallen is offline miallen  United States
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Quote:
Originally Posted by Michael Bean View Post
I strongly recommend separating the signal ground from the power supply ground, that will minimize the possibility of inducing power supply noise in the signal lines. I do this in everything I build.
Do you mean like the following?

Click the image to open in full size.

But with a separate ground wire running back to the power supply ground?

Or are you suggesting that the signal ground actually have no connection to the power supply ground at all?

Also regarding signal ground, I was going to twist signal ground wire around all wires coming off the board (the red pads indicate wire locations). Is this practice of twisting a signal ground around wires recommended? Or is it only useful under certain conditions? What are those conditions?
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Old 5th April 2011, 11:50 PM   #6
miallen is offline miallen  United States
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Quote:
Originally Posted by miallen View Post
But with a separate ground wire running back to the power supply ground?

Or are you suggesting that the signal ground actually have no connection to the power supply ground at all?
Can no one follow through with a comment about this? I would really like to understand it.

Regarding separating signal and power supply ground, does that mean just having separate wires back to the regulator or actually not connecting the signal ground to power supply ground at all?

Mike
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Old 6th April 2011, 01:30 PM   #7
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Audio Component Grounding and Interconnection

Run the signal ground to the star separately from the power supply ground, don't leave it floating.

Follow the recommendations in the linked article for all of your input and output connection grounds - a star of stars is probably a good idea. I use twisted pairs for internal signal connections, others suggest a small shielded cable for unbalanced signals. Not sure if there is an advantage or disadvantage to either.

Last edited by BobEllis; 6th April 2011 at 01:34 PM.
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Old 7th April 2011, 04:27 PM   #8
JAY X is offline JAY X  Spain
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Hi All,

I also do separate audio ground and supply ground, in the circuits i'm building on breadboard : Diff amps, bal out, etc.. but after reading "audio component grounding and interconnection" i don't know if it would be a good practice to run the audio ground wire from the middle of the audio ground bus instead of the end, in a sort of "star" point arrangement.

Thank you very much,
JAY X
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