phonostage paradox

Atmasphere: The hum only occurs when hooked up to the preamp,
and then only in the MC setting, not MM.

Dear Boofer: Your phono stage has a real poor S/N rati through the MC option: 58 db!!! against the 84db on the MM option.

You can hear directly on the MM option your 301 because your PS has a non-normal MM high gain: 46db.

That PS comes with this switch:

"""" Exclusive AC polarity switch to eliminate hum """"

I don't know if you are using it.

Regards and enjoy the music,
R.

What happens when there is no cable hooked up to the input of the preamp? Does it hum then?

The signal to noise ratio in the MC section is not nearly as good as with the MM stage.