[Ikon]

I'm just building a new power supply for my amp and I'd like to add some serious low pass filtering before the regulator. I probably shouldn't put more than 5000µF in that position and I can use about 6 Ohms (to limit the voltage drop).

Is there any point in "spreading" these 5000µF/6R over two or three filter stages or is it better to just use one big cap and one 6 Ohm resistor?

And since we're at it: Exactly what does a pi-filter (CRC) better than a plain RC-filter? Wouldn't it have the same corner frequency given the same resistor and cap size?

 

[Jambo]

Quote:

Originally Posted by Ikon /img/forum/go_quote.gif Is there any point in "spreading" these 5000µF/6R over two or three filter stages or is it better to just use one big cap and one 6 Ohm resistor?

Spreading it out introduces more poles so you get a steeper roll-off. Probably more expense and more space though.

Is this a common thing to do around these parts? Strikes me as a pretty bad idea particularly in an amp, due to the ripple that you hinted at that will be induced by varying current.

 

[jcx]

if the RC pole is near or below the regulator's load rejection corner freq ( 100-1K Hz typ) then the power supply performance is improved up to the point that load current causes enoungh V drop to reach the regs dropout V limit

usually LC is used to avoid the DC V drop but headphone amps can be hugely inefficient at little cost

multiple sections are more efficient in parts size/HF rejection, more, smaller physical sized caps can have lower esl which ultimately limits the HF atten

 

[ericj]

get the free power supply simulator from duncan amps and simulate your PS - it's pretty accurate.