# Pin-1 problem



## atomik (Apr 8, 2009)

Hi !

I've read the AES paper about pin-1 problem. I understand the common impedance problem. But after I read this:

Pin 1 Revisited If I look at the figure 5, I don't see the problem. 

There is no common impedance and even if the "SIG REF" is modulated by RF noise, all the ground plane is at the same potential (even if it's not fixed) by neglecting the ground plane impedance.

Thanks for your help !


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## Speedskater (Dec 23, 2007)

Here is some more reading on the pin #1 problem.
Jim Brown of Audio Systems Group is the AES committee chair on EMC.

http://www.audiosystemsgroup.com/Pin_1_Revisited.pdf
http://www.audiosystemsgroup.com/Pin_1_Revisited_Part_2.pdf
http://www.audiosystemsgroup.com/Shield_Current_Induced_Noise.pdf
http://www.audiosystemsgroup.com/SCIN-2.pdf


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## TimmyP (Jul 27, 2008)

atomik said:


> Pin 1 Revisited If I look at the figure 5, I don't see the problem.


The problem may not be understood from the drawing until one re-reads the description. In figure 5, instead of Pin 1 being connected to the mic's case as close as possible to Pin 1 (either directly mechanically or by the shortest possible wire), the connection is via a wire of some length - a length long enough to have a significant inductive reactance at RF frequencies. RF frequencies can produce a signal in the wire that becomes part of the signal.


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## lcaillo (May 2, 2006)

TimmyP said:


> The problem may not be understood from the drawing until one re-reads the description. In figure 5, instead of Pin 1 being connected to the mic's case as close as possible to Pin 1 (either directly mechanically or by the shortest possible wire), the connection is via a wire of some length - a length long enough to have a significant inductive reactance at RF frequencies. RF frequencies can produce a signal in the wire that becomes part of the signal.


This is correct, only I would reword that last sentence. The RF signals are there and the inductive reactance in the wire creates an antenna that becomes part of the circuit.

Grounds are never perfect because every connection has some components of resistance, capacitance, and inductance. The problem is that at audio frequencies these are not large factors, but when you start getting into even low frequency RF a circuit behaves differently and these may be come significant considerations.


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## Speedskater (Dec 23, 2007)

Perhaps Tony Waldron has the best papers on this subject:

http://www.fragrantsword.com/twaudio/

The papers are rather technical, not easy reading.


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## atomik (Apr 8, 2009)

Thanks for all your informations !


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