Hey guys. I recently had my ABM500 sent to Walter Harley to have it modded to sound clearer. A lack of brightness or top end has been a complaint of many folks who own this great head and I am no exception. I found out from Walter's last e-mail that my hunch about the amps design was correct. There is a 6db low end boost and a steep high frequency cut off (3.5khz) built in to the circuit. Walter Changed some component values to correct this as well as to remove some less than desirable interaction between some other circuits. Before he ships the amp back to me, he is going to try reducing the overall distortion of the output circuit if possible. All of this for a very reasonable price. I'll let you know how this awsome amp has changed once it is in my possesion.