advices needed to mod SACD's Lowpass filter?

[xxie24]

Hi, I has a Pioneer DV-676A universal player. I did various mods to it including adding sperate PSU, OPamp change, Cap change. The results is quite good, but one problems remains that I can always hear some hiss even when the volume turn to 2 clock through the headphone, also the sound turns out too bright.

The DAC's delta-sigma type (Edited: PCM1742 from TI), it has -55dB stop-Band attenuation, which I don't think is great. Could this causes the problem? Is that means I need design a really effective lowpass filter?

Also considering SACD's frequency reach 48kHz, normal CD reach 22KHz. what will be the best cut-off frequencey for the filter? (currently i has zero SACD disks, so I more prefer to design a 22Khz filter).

Any advices? thanks

 

[Garbz]

xie the dac is a PCM1742. but the stopband you mentioned is correct.

I'm not sure if the same applies to low pass filters, but high-pass filters cause phase distortion around them, which is why a high-pass filter with the -3db Point at 20hz turns the bass to mud. So the rolloff frequencies needs to be way below the audible range as well as any phase distortion that go with it.

 

[xxie24]

Quote:

Originally Posted by Garbz xie the dac is a PCM1742. but the stopband you mentioned is correct. I'm not sure if the same applies to low pass filters, but high-pass filters cause phase distortion around them, which is why a high-pass filter with the -3db Point at 20hz turns the bass to mud. So the rolloff frequencies needs to be way below the audible range as well as any phase distortion that go with it.

You are right, it is PCM1742 as DAC in that player.

For the universal player, I am just wondering how could other player to balance low pass filter's design between SACD and normal CD. I havenot be able to find out Pioneer DV-676's filter's cut-off frequency, but I only know it is a second order filter and I assume it is around 48Khz. Because of the DAC only has -55dB stopband attenuation at 0.5 sampling frequency, it make me worried about the normal CD's performance near the 20Khz.

There are some CDP's mod which change the 2nd order filter to 1st order filter in the hope of improving high frequence SQ. Some DAC like NOS even does not have filter at all! What is the catch for this issue?