Class AB input coupling cap question - Page 2

AndrewT · 27th December 2012, 12:08 PM

Barley and Tand,
What RC time constant is required for passing the FULL AUDIO bandwidth of 20Hz to 20kHz?

Barleywater · 27th December 2012, 02:46 PM

In: Question on input dc blocking capacitors #32 I show simulation of simple 1st order high pass filter with -3dB point at 6Hz. Response is effectively flat >20Hz, but phase skewed by group delay, as exhibited in square waves depicted. This is accurate representation of how low frequency transients get re-ordered, sometimes quite audible.

This is another reason why 10x is often suggested in choosing cutoff frequencies.

Regards,

Andrew

AndrewT · 27th December 2012, 04:15 PM

Are you saying that 10times wider than required bandwidth is adequate, or are you saying that 6Hz (about 3times), or are you saying some other value for RC?

What about the HF end of the bandwidth?

Barleywater · 27th December 2012, 04:59 PM

10x, so as elsewhere: in the neighborhood of 2Hz and lower for cutoff frequency.

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27th December 2012, 12:08 PM	#11
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Barley and Tand, What RC time constant is required for passing the FULL AUDIO bandwidth of 20Hz to 20kHz?

27th December 2012, 02:46 PM	#12
Barleywater diyAudio Member Join Date: Jan 2008	In: Question on input dc blocking capacitors #32 I show simulation of simple 1st order high pass filter with -3dB point at 6Hz. Response is effectively flat >20Hz, but phase skewed by group delay, as exhibited in square waves depicted. This is accurate representation of how low frequency transients get re-ordered, sometimes quite audible. This is another reason why 10x is often suggested in choosing cutoff frequencies. Regards, Andrew

27th December 2012, 04:15 PM	#13
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Are you saying that 10times wider than required bandwidth is adequate, or are you saying that 6Hz (about 3times), or are you saying some other value for RC? What about the HF end of the bandwidth?

27th December 2012, 04:59 PM	#14
Barleywater diyAudio Member Join Date: Jan 2008	10x, so as elsewhere: in the neighborhood of 2Hz and lower for cutoff frequency.