The filter is R7-C3-NPN transistor. They say that this filter supress the noise with 50dB. I'm wondering how this work. Does this filter hava a special name?
I don't think this filter can fulfill your expectations ..
Perhaps more efficient solution, as far as the noise attenuation is concerned, would be to introduce proper shielding + RF-choke(s) on both rails supported by decoupling capacitors (1-100µF electrolitic and 100pF+100nF ceramic) ..
Regards,
IanP
niose in what freq-range you concern most:?:
if low freq noise is concerned , the tradition linear regulator already provide good noise rejection(if built with low noise voltage reference).
if high freq noise is more concerned, try LC or CLC or even more complicated circuit.