Here is more explanation from a previous question. I will say the Toroid ll was an upgrade that you can definitely hear a great improvement in sound quality right off the bat. Ask others who have the Toroid ll interfaces or have upgraded.
I did all the work in conjunction with discussions with Dr. West. He is a great person and willing to talk to anyone with an interest in speakers (even if you want to modify or upgrade them). Most of what I did was just part replacement to better components. The better components were bigger so they had to be housed outside the interface. I put what components I could on the original interface so it fit within my A1 oak cabinet. The other components were housed in the computer box in the picture (I would change this if you want it to look good). The computer box can be placed anywhere but I put it right behind the speaker. Note that the computer box has three connection points. The single connection point hooks to the single connection point on the interface. The two connection points on the computer box hook to the power amplifier connection points on the interface (Red on the computer box goes to + on the interface and Black on the computer box goes to – on the interface) You can use plain wire, spades, or banana plugs for the connections. You connect your amplifier to the interface in the normal way.
The only major change other than component upgrades (and figuring out how to put this all together (I’m an electrical engineer) was changing where the crossover point (e.g. where the Toroid ll takes over from the Square transformer). The upgrades were inductors, resistors, and paper in oil capacitor. Using the Toroid ll with an older interface provides benefits but really does not take advantage of the higher saturation capability of the Toroid ll). The best benefit is allowing the Toroid ll to manage a wider bandwidth. I believe a standard Toroid l interface operates at 550Hz and above. Dr. West said that the Toroid ll can operate to about 250Hz. What I will say is that you can hear the benefits of the Toroid ll just by popping it in.
Under Dr. West’s advise, I used the 36uf capacitor with 12 ohms of resistance to increase the bandwith of operation of the Toroid ll to maximize it’s capability. That is the large capacitor in the computer box and the two non-inductive wire wound resistors in the computer box. I believe the standard interface uses a 24uf capacitor and 8 or 12 ohms of resistance with the Toroid l. They are overkill but are all high voltage devices.
The only other modification was taking out the brilliance control. This is just a cheap potentiometer (variable resistor) that everyone seems to complain about. I believe it is 8 ohms. I measured my setting which was 5 ohms and used 5 discrete 50 Watt metal film resistors. Although they didn’t need it, I attached them to the heat sink in the computer box. I know others have bypassed this completely (e.g. shorted it out). You could easily short a resistor out (they are under the heat sink) with a piece of wire or add resistors to change the tone (if you know how to solder).
As stated, there are no changes to the schematic of the interface just parts upgrades and a change in the frequency of operation.
I hope this helps. Let me know if you have other questions.