Our field coil drivers all require a power supply, sold separately. Any DC power supply may be used, although going beyond 17 volts is not covered under warranty. We can recommend an original Feastrex power supply without reservation; we sincerely believe it will be difficult to surpass the quality of our PSUs at any price point. After extensive trials involving power supplies of many types, we are confident that our power supplies realize a level of performance that can not be easily surpassed. All the parts are of the best quality, including superb R-core transformers specially wound for us by Japan’s leading manufacturer of this type of transformer. Particularly noteworthy is our use of what we believe to be (by a large margin) the world’s most advanced solid state rectification diodes. Our PSUs were developed with the special assistance of the creator of these diodes, Mr. Saburo Degawa.