I built a EQD Ghost Echo this weekend and it sounds great, but there is a noticeable volume drop. I built an LPB1 with a trimpot and I have it after the reverb in between the board and the 3pdt. The LPB1 calls for a 100k trimpot, but I only had a 5k on hand. It's got plenty of volume on it, so I've been able to get it to unity, but I'm wondering if there's a change to the sound or tone of the effect with the 5k trimpot. I'm not hearing a difference, but I'd like to know if I did something stupid or not.
-Kris
Nope, it's just volume and that's it
The final output cap does interact with the volume pot to form a high pass filter. On the schematic I've got for the LPB1, it calls for a 100nF output cap. With a 100k pot in there, that's going to put the corner frequency of the filter at about 16Hz. With a 5k pot in there it's going to be about 318Hz. So, I'd expect that you will see a bit of bass cut with this. You could reduce the corner frequency by moving to a 1µF output cap. That would get you to a corner frequency of about 30Hz and would be pretty much inaudible for a guitar.
The other possible interaction is the match between the output impedance of the transistor gain stage and that of the pot. Although, 5k is probably close enough to the output impedance for it not to matter.
Thanks for the responses! I don't notice any bass cut, but I'll play around with it some more. I have a 100k trimpot on the way, just in case.