How to calculate a low pass filter for DSD? like other LPF for example if I want a LPF of 50kHz R 32,83 ohms & capacitor 100nF?
A low pass filter is a low pass filter, DSD or not. But component values depends on the impedances of the circuits driving and loading your filter. And what degree of filter do you want? With what ringing characteristics?
A simpler question - what is it that you are trying to do?
I want to take off the DAC using LPF followed by one hi-gain tube stage, can be done using the poste values for a LPF of 50KHz?
You could try it with an opamp unity-gain buffer amplifier before and after the filter. Then, if you must, check to see what happens without each buffer.
No. Sounds like you are talking about a simple first-order RC filter. That will only have a slope of 6 db/oct. So -6 dB at 100 KHz, -12 dB at 200 KHz, -18 dB at 400 KHz. Not very effective, is it?
I haven't tried, I want to be sure before to connect something, if I have to try other filter suggestion will welcome.
OK, but it sounds like you need help with much more than just a few component values. Doesn't your DSD DAC already have an output filter?
I suggest a 4th order LC filter for DSD. After all you'll want to aim for something approaching 120dB rejection at the switching frequency, which for DSD64 is 1.4MHz.
Agree, you need something much more complicated than just a first-degree filter - but a lot also depends on the HF behaviour of your tube stage.
Ah, I see. What kind of circuit drives your filter? What is the HF behaviour of your tube stage?
I don't know the HF behaviour of the tube stage, the tube stage to be used in attached pic.
Attachments
Sorry my ignorance:
What Low pass filter: Butterworth or Chebyshev?
What is the corner frecuency necessary?
What kind of filter: series or shunt?
Butterworth or Chebyshev would be fine - I suggest Butterworth as its simpler to design. The corner frequency depends on you - perhaps 50kHz -3dB would be fine as a first attempt.
A 4th order LC would have two series inductors and two shunt capacitors, followed by a resistive termination
<edit> Attached a schematic based on a design I did for an ESS DAC. Its Butterworth but 30kHz -3dB.
A 4th order LC would have two series inductors and two shunt capacitors, followed by a resistive termination
<edit> Attached a schematic based on a design I did for an ESS DAC. Its Butterworth but 30kHz -3dB.
Attachments
Last edited:
What is more important for you - steepness of the filter, or minimizing ripples?
As low as possible - I would put it at 22-25 kHz.
When you go beyond a simple first-order RC filter, it doesn't really make sense to talk about a series or shunt filter - if you implement the filter as a passive filter, it will have both shunt elements and series elements, and be a fairly complex filter with both inductors and capacitors - and making a 4th order passive filter is not easy! Usually some active buffer elements are used.
If you want to go ahead anyway, all the required formulas are here and here.
I am all for experimenting, but I have to ask what it is that you are hoping to accomplish? You are not likely to produce anything that has superior sound quality compared to systems designed by professional designers, and there is a real risk of burning out your tweeter or causing some other damage to your speakers.