[sachu]

After recently comparing my DAC to other higher end DACs, i have noticed that there is still room for improvement with my own.

I am trying to look at what can be done to modify the sound (for better or worse only after listening would i know). Looking at the current configuration of the reconstruction filter on my DAC it seems it is using a passive first order LP filter followed by a 2nd order Sallen key filter.

I was wondering what changes i can do to this configuration.

Is it possible to just have a simple 2nd order passive filter here by doing this
I could possibly reduce the corner frequency further if that would help.

 

[jcx]

2 ~ equal frequency cascaded RC poles will have a very low Q, the frequency will start rolling off way below the "corner" frequency

with just 1 real pole in front of the Sallen-Key you can implement a 3rd order filter with Butterworth response for high frequency flatness in the pass band

it could be OK to have a extra very high frequency pole in front of the properly aligned 3rd order section with the added pole at 20-100x of fs - it would still do some good with high oversample rate converters like most modern delta-sigma types

an unobvious improvement to the Sallen-Key is a low Z buffer in the loop to reduce output impedance and lower the feedthru, permitting higher ultimate attenuation than without the buffer with typical op amps having 50 Ohms or more open loop output Z

the inverting "multiple feedback" biquad low pass can be better in ultimate attenuation than the Sallen-Key but does load the source more