coupling capacitor. - Electronic Circuits Projects Diagrams Free

Gaston · 31st May 2007, 05:51 PM

in the isd1100 spec sheet it recomends a coupling cap between the output and the input of the amp. my question is, will this filter out any of the frequncies? i know a high pass filter uses a cap and a resistor. and being that this doesn't have a resistor i don't know if it will act as a filter. my next question is, how do you calculate the size of the capacitor?

Papabravo · 31st May 2007, 05:55 PM

As a first approximation you compute the capacitative reactance over the frequency range of interest.

Code:

Xc = 1 / (2*pi*f*C)

What you want is a reactance that is small with respect to the input impedance of the next stage over the frequency range of interest.

Gaston · 31st May 2007, 06:42 PM

so Xc = the input impedance of the amp? and would you use the highest frequency you plan on passing or the lowest?

oh i see, Xc needs to be small in comparison to the input impedance.

audioguru · 1st June 2007, 02:57 AM

The frequency where the Xc equals the input impedance is the cutoff frequency. The level at that frequency is attenuated by 0.707 times which is 3dB, half power, a small drop. For a highpass filter, lower frequencies are attenuated more at the rate of 6dB (half the level) per octave. The response is flat at about 5 times the cutoff frequency.

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31st May 2007, 05:51 PM	(permalink)
Gaston	coupling capacitor. in the isd1100 spec sheet it recomends a coupling cap between the output and the input of the amp. my question is, will this filter out any of the frequncies? i know a high pass filter uses a cap and a resistor. and being that this doesn't have a resistor i don't know if it will act as a filter. my next question is, how do you calculate the size of the capacitor?

31st May 2007, 05:55 PM	(permalink)
Papabravo	As a first approximation you compute the capacitative reactance over the frequency range of interest. Code: Xc = 1 / (2pif*C) What you want is a reactance that is small with respect to the input impedance of the next stage over the frequency range of interest.

31st May 2007, 06:42 PM	(permalink)
Gaston	so Xc = the input impedance of the amp? and would you use the highest frequency you plan on passing or the lowest? oh i see, Xc needs to be small in comparison to the input impedance. Last edited by Gaston; 31st May 2007 at 06:45 PM.

1st June 2007, 02:57 AM	(permalink)
audioguru	The frequency where the Xc equals the input impedance is the cutoff frequency. The level at that frequency is attenuated by 0.707 times which is 3dB, half power, a small drop. For a highpass filter, lower frequencies are attenuated more at the rate of 6dB (half the level) per octave. The response is flat at about 5 times the cutoff frequency. __________________ Uncle $crooge