They change out the caps and alot of the resitors, they change the tubes in the line stage and the wire going to the main outs and from the selecter swicth with silver wire, the line stage tube sockets are changed to gold plated ceramic, and they do some work to the power supply. Mark say the unit will sound better than you could ever thought the little pre-amp could sound. He`s working on the ones for the model 88 amp should be ready in a month.I f you don`t have these you need to get these asap the cardas caps are just unreal as to the noise they will reduce in the pre-amp. Greg
