I fixed a dodgy switch on this for a friend who picked it up for a good price (well, good for Norway at least!). The effect is quieter than the bypass level so I've been given the thumbs up to add a boost or some dirt, and there's plenty of space inside.
So, any suggestions? The Holier Grail takes 18v so I guess I need to add a voltage regulator to bring it down to 9v.
if you're looking for a clean boost, I'd suggest the EHX LPB-1. It's small and easy enough to build on breadboard. Are you planing on putting it on a switch or adding it permanently into the chain.
I have a board designed for the LPB-1, which is the same as the SHO you've just built. Same footprint, wiring and optical bypass. You can also omit the switch with two jumpers.
https://oshpark.com/shared_projects/6oY6CUcg
Looking at the schematic there shouldn't be any need to add an extra circuit, if you can locate R28 (Direct Out) & R34 (Main Output) they should both be 10k and if you increase them that should bring the output gain up.
I was thinking to permanently add it to the chain, set with a trimpot inside, so the LPB-1 would work well. Swapping those resistors should be easy enough though. Thanks for the tip Scruffle - I tried looking but haven't managed to find a complete schematic, so if you don't mind PMing me that, that would be great. Perhaps then I could figure out how to shoehorn an effect into the reverb path only. The gate function on this thing is quite fun but it's pretty abrupt, so if I could smooth the decay a little that might make it more versatile.
If I wanted to add the Cave Dweller 2015, do I need to worry about the 18v power from the Grail's PSU? I assume the electrolytic caps should be at least 25v, but is the 78L05 and 1n5817 going to handle the extra volts?