Hi. First, sorry for me bad English. I do this post to ask for help to resolve a problem with this amp. At firts it worked fine but a day I try to use the loop effect and then amp started to drop the volume when I disconnect the loop. Now don't have sound from the Input Guitar. But if I connect the guitar in the RETURN LOOP, sound. I cleaned all the jacks, and tested all the potentiometers and don't have results. Also, Headphone jack input sound very low. I think problem is in preamp section but people from TECH21 tell me that he can't sent me the schematic. A short video. In some position of SansAmps the guitar is very very low but sound. https://drive.google.com/file/d/1YkgsX2M0AwSWOurArOiT2pUtuXMuyjgl/view?usp=sharing THANKS!