Preamp for Pass Labs X-150.8

erik_squires
I still think that most preamps have too much gain, and therefore too much unnecessary noise. :)

Eric is correct, that’s why all that’s needed is unity gain (no gain) preamps these days, whether active or even passive if the poweramp is >33kohm input impedance.

That’s why the Schiit Freya is a good choice, it can be, passive, low gain tube, or low gain solid state with Balanced or SE connections. You can have it all and choose what mode sounds best for you for just $699 refundable if not happy.

Cheers George

 Rothwell attenuators

As for Rothwell Attenuators, they can be hit or miss, as no one knows what  value resistors were used inside to make a voltage divider for each of the - db ratings. And they can cause an impedance miss-match between pre and poweramp, or between source and preamp depending on where they were used.

Cheers George  

We think of a preamp as a "variable gain" device, but it's actually a fixed gain device, with volume after. 

I think you'll find, an active preamp is a volume control with a fixed gain stage "after it". The volume control reduces the source signal level and the output stage is at a fixed gain.
The only time there is a gain stage in front of the volume control is if it has a phono stage that also has gain.

Cheers George 

Preamp for Pass Labs X-150.8

The 150.8 only needs 1.7v in for full wattage output, and most sources even many phono stages are >2v output, so you should look for a preamp with low gain otherwise you may not be able to use much of the volume control range before it’s too loud.
Also input impedance of the 150.8 is 50kohm se and 100kohm xlr which is a good candidate for a passive preamp.
Schiit Sys http://schiit.com/products/sys

Or the very versatile Shiit Freya, 3 in one http://schiit.com/products/freya which can be used as passive unity gain, low gain tube, or low gain solid state.

Cheers George