I cant recall if someone here has put all the mods in the same place - there was one that came out just recently about matching the hfe of the input transistors on the driver boards and replacing the stock carbon resistors with metal film. That was the last one I did. There was also one before that that involved replacing a couple of ceramic caps on the driver boards with polystyrene caps. One thing to look for - if you are removing the driver boards be incredibly careful with extracting the round metal heatsink-mounted transistors from its spring-loaded metal socket. replacements of these can be a bugger to locate. Before I did the mods on this amp I thought it sounded completely arse. Lifeless, flat, no stereo image and most importantly - NO BASS!