RC filter bias supply question

[Gaz]

I'm using this bias supply filter arrangement on an amp, am I'm wondering if the first filter cap is "doing" anything since there is no resistor preceeding it to form an RC filter. Thanks for any guidance.

[mooreamps]

I'm using this bias supply filter arrangement on an amp, am I'm wondering if the first filter cap is "doing" anything since there is no resistor preceeding it to form an RC filter. Thanks for any guidance.



[ATTACH=CONFIG]18257[/ATTACH]

It looks like a PI filter to me... I use the same, except I tend to put the diode on the ground side of the winding, instead of the hot side.... No special reason for that, just my personal preference... Sure the current load on a typical bias supply current is quite low, thus allowing the caps to charge to almost full value on a half-wave rectifier circuit... But the amount of measured ripple on the output quite low, and well with-in acceptable limits.... Also, as a side note, the 60 hz ripple is less ; how should I say ; a little less "audible" than say 120 hz...

-g

[diagrammatiks]

the first cap is the reservoir. same as the hv winding.

[Gaz]

Thanks guys. "Pi filter," that was the term I was missing!