I have been disappointed with the tone of my Mu-Tron III since having it rebuilt by CAE Sound. They did a very tidy job (drilled out and replaced corroded screws, very neat job on reconstructing the battery plate and added an effect active LED) but there is no significant quack after having the standard re-furb kit installed.
To better qualify, there is no quack using an active bass whilst powering the unit using battery clips to a PP2+. Also, the unit distorts when the gain is set past 8 o'clock.
The PP2+ is my first preference as a power supply - it's smaller than the standard non-attached AC power supply and it doesn't need replacing when I invariably leave the power switch on.
I think I will try using the two sag controlled points on the PP2+ and a passive bass before I put it away in the back of the cupboard.
At the moment I'm a little disappointed given the initial cost, plus import duty, plus the cost of repairs and rebuilding, plus shipping to and from the states, plus import duty on the rebuilt unit...