The CS43122 only needs a simple analog filter at the differential outputs. In the datasheet, it's two 300R in series with each output followed by 2200pf between + and -. When I put this in LTSPice, it shows a pretty big dB dip and phase shift at the high end.
Would it be allright to change this by say using a lower capacitance, or otherwise modifying the values? Or is there a reason not to do this?
Would it be allright to change this by say using a lower capacitance, or otherwise modifying the values? Or is there a reason not to do this?
Analog Filters
Hi Prune,
On the Analog Devices website or that of Texas Instruments is a program to calculate balanced filters.
www.analog.com
http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/filter/filter.html
www.ti.com
Search for FilterPro(R)
Prune said:Still hoping for a reply
Hi Prune,
On the Analog Devices website or that of Texas Instruments is a program to calculate balanced filters.
www.analog.com
http://www.analog.com/Analog_Root/static/techSupport/designTools/interactiveTools/filter/filter.html
www.ti.com
Search for FilterPro(R)
I'm using jwb's desing:
http://atari.saturn5.com/~jwb/43122.png
There are no opamps. The CS43122 has voltage output. jwb used the same passive filter as in the CS43122 datasheet (2 resistors and a capacitor), followed by a voltage follower.
When running this output stage in LTSpice, lowering the capacitor value slows falloff in the high frequencies. I was just wondering if there would be negative side effects in doing that (I want to even out the frequency response).
http://atari.saturn5.com/~jwb/43122.png
There are no opamps. The CS43122 has voltage output. jwb used the same passive filter as in the CS43122 datasheet (2 resistors and a capacitor), followed by a voltage follower.
When running this output stage in LTSpice, lowering the capacitor value slows falloff in the high frequencies. I was just wondering if there would be negative side effects in doing that (I want to even out the frequency response).
site could be of help.......
I do not think it is that bad. It falls less than a dB and 9degrees phase shift, or i might have done something wrong.
I am also kind of interested to see what people think of these low pass filters. If i look at the CS43122 spec it seems that if you are running it in mode0(whatever that is) the attenuation is at least 100dB in the stopband so i would guess that this circuit would not cause any trouble in any amplifier that follows it even without filter.
Is it important sounwise to have absolutely flat frequency response 20-20k?
I am also kind of interested to see what people think of these low pass filters. If i look at the CS43122 spec it seems that if you are running it in mode0(whatever that is) the attenuation is at least 100dB in the stopband so i would guess that this circuit would not cause any trouble in any amplifier that follows it even without filter.
Is it important sounwise to have absolutely flat frequency response 20-20k?
Yes, it falls just under a dB; however, I'm getting close to 24 degrees phase shift. Considering that the DC blocking output capacitors shift the low end phase to the other direction, that's pretty large.
I tried without a filter with my tube headphone amp, and didn't notice a problem. I'll be making the Aleph-X, so I wonder if that might be a problem.
As I don't have any smaller SMD caps for this, I wonder if it would be OK to just put two of these 2200pF in series.
I tried without a filter with my tube headphone amp, and didn't notice a problem. I'll be making the Aleph-X, so I wonder if that might be a problem.
As I don't have any smaller SMD caps for this, I wonder if it would be OK to just put two of these 2200pF in series.
Prune said:
http://www.capacitors.com/picking_capacitors/pickcap.htm
This article talks a bit about resonance frequency
The basic reason for the lowering of the resonant frequency is found on the following link.
http://www.wima.com/inductance.htm
The effect is shown on the following graph, see the last page in the pdf file
http://www.elfa.se/pdf/65/06571301.pdf
But if the point is well beyond the highest frequency out of the DAC that you want to attenuate it is ok.
http://www.wima.com/inductance.htm
The effect is shown on the following graph, see the last page in the pdf file
http://www.elfa.se/pdf/65/06571301.pdf
But if the point is well beyond the highest frequency out of the DAC that you want to attenuate it is ok.
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