The PDF posted was extremely helpful, as have several of the threads talking more about the MVB.
My RM50 has always been a little kooky with the Master Volume Boost. Occasionally while playing, with nothing plugged into the MVB jack, the amp would suddenly go to max volume and scare the living crap out of me considering it's the amp I use at home at bedroom levels. I rectified this by taking an old 1/4" plug and soldering the lead to the ground. It only sticks out of the back of the amp a little. Recently the solder must have broken or something because the amp did it again, causing me to research this.
So, if anyone has built the pedal in the above schematic, why do they use a 4K7 resistor? My research tells me with a 3.8 V LED it should have a 520 ohm resistor. I know virtually nothing about electronics.
I was researching for a different project and saw this recently, thought I'd ask? I tried a 1k resistor between a 9V source and a 3.8V LED and got no light, so it seems like 4K7 would be even more overkill.