Ghost echo (spirit box) unity volume problems

[IgorAnnikov]

Hi, built the spirit box, sounds great but it still sits below unity volume when it is engaged. Even when the depth control is all the way down. As far as I know the depth just mixes in the wet signal with the dry.
It's a b2k pot and it measures around 1.9k.
Should I increase its resistance with a resistor in series or is there a better way to solve this problem?

Thanks

 

[Robert]

Increase the value of R4.

 

[reubenreub]

I just built one of these with the same issue. Ended up replacing R4 with a 20k trimmer to get the volume just right.