Formula for CR Xo pole?

ro9397 · 26th August 2011, 07:35 PM

For a series capacitor between a line-level output and line-level input, is this the formula to compute the Xo pole?

Fc = 1/2piRC

R = input Z
C = series capacitor value

DF96 · 26th August 2011, 08:51 PM

Not sure what you mean by Xo. The formula you give is approximately correct for the LF rolloff point. The full value is
f = 1/ (2 pi (R1+R2) C )
where R1 is output impedance (or previous stage), R2 is input impedance (of next stage).
As R1 is usually much smaller than R2, and capacitors often have 10% or 20% tolerance, the simpler formula is usually close enough.

ro9397 · 26th August 2011, 09:00 PM

Xo, crossover, sorry!

Your math makes much more sense than mine. All I need now is the output impedance of one of the source components.

Thanks very much for your kind reply.

26th August 2011, 07:35 PM	#1
ro9397 diyAudio Member Join Date: Jan 2007 Location: No. Utah	Formula for CR Xo pole? For a series capacitor between a line-level output and line-level input, is this the formula to compute the Xo pole? Fc = 1/2piRC R = input Z C = series capacitor value __________________ Jimbo "Television is the poor man's whiskey." Russel Baker

26th August 2011, 09:00 PM	#3
ro9397 diyAudio Member Join Date: Jan 2007 Location: No. Utah	Xo, crossover, sorry! Your math makes much more sense than mine. All I need now is the output impedance of one of the source components. Thanks very much for your kind reply. __________________ Jimbo "Television is the poor man's whiskey." Russel Baker

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26th August 2011, 08:51 PM	#2
DF96 diyAudio Member Join Date: May 2007	Not sure what you mean by Xo. The formula you give is approximately correct for the LF rolloff point. The full value is f = 1/ (2 pi (R1+R2) C ) where R1 is output impedance (or previous stage), R2 is input impedance (of next stage). As R1 is usually much smaller than R2, and capacitors often have 10% or 20% tolerance, the simpler formula is usually close enough.

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