SMPS + Class A microphone preamp discoveries

[Potato Cakes]

For me I am not going to change a thing. I have been using this circuit for all kinds of audio projects and the results are quite remarkable. Still haven't figured out the capacitance multiplier then regulator issue but knowing about it helps the design phase.

Thanks!

Paul

 

[RSRecords]

Is there a schematic that you're using for the CM? I'm working with a mean well 24v smps that's causing some noise issues. I've used them before without issue but I think the class A audio circuit may be amplifying the issues.

edit: never mind missed the earlier schematic

 

[Cqwet Dbdfte]

Using SMPS for low noise will require added effort.
The typical SMPS has a switching frequency somewhere near 250kHz, but can be higher, 2 MHz is possible. Higher freq means smaller transformers and inductors, and trading conducted noise for radiated noise. Pick your poison.
The output is basically a triangle wave at the switch frequency with added HF spikes on the min and max on the triangle.
All that needs to be "shaved off", using all kinds of filters. Housing these animals in a separate shielded box should be safer starting position.
2x line frequency ripple will not be an issue, and hi efficiency small size is a bonus.
A scope, preferably with some FFT function will be very useful.
Some excellent work in SMPS has been done by AD with their "silent switcher 3" series, but are not off line what I've seen.
Classically, clean SMPS had linear post regulators.
So much fun.