Just purchased a Belles 150A Reference amp. Watch should my preamp be..

Is there a simplified video crash course or articles that help me understand why those numbers should be alarming to me.

No not really that you would understand.

To put it simply as possible, most sources have over 2v output, your 150A only needs 1.27v in, for it to give full watts output.
So you don’t need more gain from an active preamp. What you need is a preamp with little or no gain.
This is why the Schiit Freya is a good match as it has little or no gain, depending on which output you use.

Cheers George

I looked up the 1.27V figure and it seems that may be associated with the 150A Belles and not the 150A reference, which has an input sensitivity of 1.4V according to another page. Still, much less than the 2V. What would an acceptable small amount of gain?

What would an acceptable small amount of gain?

Still something like the Freya, would be the best as it’s the only one I know of with low or nothing gain, and you have the choice of tube, solid state or passive output.
And it's remote volume with the best, 128 position relay controlled, multiple inputs, and outputs, single ended or balanced. And you can sent it back if you don't like it.  

Cheers George

So a very nice tube phono stage such as a Cary or Fosgate would have too much gain and therefore would have a slight background noise?

Anyone on the forum have experience with the Belles 150a reference amp for vinyl playback? If so, phono stage recommendations? Looking into the Schitt Freyr, but there must be more options as it has been an much lauded amp.