Questions about the GEOFEX "Cheap 'n' Good" polarity protection

[earthtonesaudio]

I've recently become fascinated with all things power supply-related, polarity protection and low-dropout filtering being at the top of the list.

While reading about current sources/sinks ( http://www.audioxpress.com/magsdirx/ax/addenda/media/jung2778.pdf ), I suddenly thought of the GEOFEX bipolar polarity protection circuit ( http://geofex.com/Article_Folders/cheapgoodprot.htm ), and the question occurred to me:



Does the GEOFEX circuit offer the noise-reduction benefits of a current source, or is a greater voltage drop required to get that benefit?
...Or does that depend on the current of whatever effect circuit is to be connected? 



I have the feeling the answers to my questions are somewhere in "basic" transistor theory, but seeing a device used as anything but an AC amplifier always confuses me.  So thanks for your patience, in advance, to anyone who answers. 

[R.G.]

Does the GEOFEX circuit offer the noise-reduction benefits of a current source, or is a greater voltage drop required to get that benefit?
...Or does that depend on the current of whatever effect circuit is to be connected? 

A greater voltage drop is required.

It is very difficult to do an active current limit in less than a diode drop without using Hall effect devices. The problem is that you have to sense the current and turn on some kind of limiter, and something like a diode drop is needed for all the simple circuits. You can do better than that, but it needs more circuitry. The circuit as shown has no constant current operation. The PNP is just acting like a switch.