I purchase the copper foil 600v 1.5uf to replace a polypropylene cap on the output of my single ended experiment kit from bottlehead, I have a burson soloist which I used to compare against my bottlehead. After the upgrade I was surprised at how much closer the bottlehead amp got to bursons resolvability. Went ahead and order a set of 0.1uf copper foil to replace the first gain stage.