Can you explain "loading"

My pre has an MM and an MC input, on the MM it has a 3 position switch for 0pF, 180pF, 390pF Labeled Phono 1 Loading....

I don't hear a difference changing it, and find nothing in my Grado Sonata papers that refers to these settings......have not had the manual for the pre in years - Carver C-1

 

Just an educated guess; but it likely is a capacitance (sp?) issue. This can change the high end frequency response of certain cartridge designs. Use a glide tone test record at low volume to confirm this.

 

could this be why some of my treble is really bright ?

Where should it be set?

 

Use your ears to see if a change makes a difference. Ears are very good tools, yes they are. The glide tone will help, but unless you are young you may not even hear the higher end of the sample.