Thanks MathU41. I had the same issue with the preamp boost section of a Rock Hard build. The TL072 would not work, so I changed it out and installed the TL071 and it worked. I noticed in a couple of photos in the “Show your build” thread that a TL061 was used in one build and a TL071 was used in another build. Thanks again for your post about this; it saved a project for me!