Sonsivri

I tried to repair one SMPS power supply of car amplifier.
It has 12v input/30-0-30 in the output.
I replaced the filter choke in the input stage with little bigger ring/round core.
But then whistle sound is coming from new choke.
Kindly help in the matter. 

If the circuit is working correctly otherwise, I'd soak the coil down with varnish or shellac to cement the windings that are moving and making sound.

Hi,
You can use bigger toroid but Inductance should be proper. Since it is for Audio purpose, things should be near to perfect. However,slight deviation can be accepted provided the coil is tightly wound. Check the windings of the toroid/filter choke and if it is loosely wound, make it tight and test. Or you can do what oldvan is advised.If it is found tightly wound, then check the inductance of the earlier choke and wound the bigger one keeping the inductance same. If you don't have the earlier one, then try with 100uH inductance. If you don't having the LCR meter to measure the inductance and not acquainted with winding, you can purchase new one.

what you are hearing is instability of the power supply, use the same type of core and turns as the old one,
try to identify the core material, the one in the original circuit may be a powdered core type toroid, and if you try to use a ferrite toroid the circuit may fail. 

Thanks to all for help.
I measured the inductance of choke from a new amp of same type.
I got the value. I checked the my new one, but it was too high.
Then bought another core & got it matched.
It is working perfectly ok now.