Design "flaw" in Quad 67CD PSU?

[Zombie]

Hello!
Glanced at the PSU schematics of my Quad 67CD to check what elcos to change as they come closer to their 10-year life cycle.
Spotted the LM2940 5V digital regulator and decided to find out more about it: http://www.national.com/ds/LM/LM2940.pdf

The output cap in the Quad CD is 2.2uF/16V, but the Application Hints recommend it to be a minimum of 22uF with no limits to its size. A search on the net says the cap is typically 100 or 1000uF.

What could an increase in the value of the cap bring for the player as a whole - soundwise? Or is there any other factor limiting this cap to 2.2uF?

Cheers
Tom

[jean-paul]

There is only one way to find out.

I would certainly change it to 100 uF standard series electrolytic capacitor, if only to ease my mind. Data sheets don't give standard values for nothing. 22 uF is the absolute minimum for stability says the National datasheet so 2.2 uF is too low.

But in practice you probably won't see even a slight change in measurements

[Zombie]

Hello and thanks for your reply!
Guess you're right. Seems like the concern is the ESR due to low temperatures rather than the size of the cap...
Do you think that this could be one of the reasons the player is rewieved as lacking in the lowest bass and not handling "big" (meaning where a lot is going on) music very well?
Read about designs that have a 0,1uF caps very close to the output/ground legs - would it give any benefit in this application?

Cheers
Tom

[hjelm]

Sorry if i am intruding somewhat.
Got so interested that i decided to read up a bit myself. The AN-1148 indicated that given that you limit the range of the load, lower max, and had a high ESR cap you could get away with a smaller cap.

Does anyone know the DC loop gain of the LM2940 and the P1 pole and the Ppwr pole or if there are any spice models for the device?