Fixing the output on a LPB-1

[carboncomp]

I want to add a boost to the end of a circuit, but at a fixed output.

Figure the LPB-1 is a good place to start, and just wonder can I just replace the level pot with fixed value resistor? 

(using this layout) http://www.beavisaudio.com/techpages/HIW/hiw1.gif

[lopsided]

you can. but you will most likely need two resistors. You are building a voltage divider.
So I would recommend use a 100K pot and tune the volume to the exact level you like.  Disconnect it to be sure nothing will interfere
Measure the resistance between the lug which was connected to C2 and the wiper (output).
Use one resistor of this value between C2 and output.
Use another resistor between output and ground (100k minus the value of the first)

[carboncomp]

Thank you for that, I now understand how voltage dividers work!