A friend told me that noise of any switching PSU can be attenuated if I put linear regulator before output. Is that true?
For example, if I want to power a +-12 V op-amp for an amplifier, I can use a switching-mode power supply (SMPS), say, with a noisy 15 V output and then from the SMPS output feed an LM7812 and a LM7912.
Will the output from LM7812 and LM7912 now have very very low noise compared to their inputs?
If this is true, this amazing as there is no need to use a transformer anymore.
Is it really correct that a heavy PSU using a transformer for Class A and B amplifiers is no longer needed?