Using noise suppression capacitors on powersupplies?

[MrZwing]

Hi

I'm designing well more like modifying a simple power supply meant to be used in audio and I have some questions about noise suppression capacitors at the AC input.

is this mostly to stabilise if you have a motor or something similar that causes fluctuation in the circuit or is it available to put it on the AC side before the transformer and bridge rectifier to gain less noise in the rest of the circuit or is it much work for almost no result?

and if it is a ok idea can I gets some pointers where to read up on choosing which values to use?

[Simon]

There are "Y" filters on most things to stop noise, but you will find it easier to filter power at low voltage DC where you are filtering the 50Hz out and any switch mode supply noise.

[MrZwing]

I will filter the DC part as well i just wondered if adding some caps on the AC side to make it a little bit stable input and for some safety (plus a fuse).

or am I just over thinking something. i have a tendency to do just that.

[Simon]

No, if you are just trying to get a clean supply for audio stuff then filter on the DC side. Decent power supplies will be well filtered already, power audio generally does not need perfect DC supplies and signal processing is easily filtered with an inductor in series and capacitor in parallel if you want to be paranoid.

[MrZwing]

Hmm true I have been thinking about putting a filter in to calm my paranoid mind. 

Have plans on buying a signal generator so i can experiment with filter circuits to get a better grasp around them, already have the oscilloscope.

then I will settle for a fuse on the AC side and make everything else on the DC part.

[tggzzz]

Have plans on buying a signal generator so i can experiment with filter circuits to get a better grasp around them, already have the oscilloscope.

I doubt a siggen will be able to simulate the interference from a motor.

I have seen motor startup transients cause clicks on an audio circuit. The solution was a common-mode inductior near the interference source; winding the mains cable several times through a toroidal ferrite ring was sufficient in that case. A clip-on ferrite inductor might be sufficient.