We’ve been using this rather simple circuit with our Hammond M3 for quite a few years now. The output level can be adjusted with the potentiometer and the switch optionally disengages the built in speaker. It works well with external amplifiers such as bass amps or a Leslie and is ideal for for recording with a passive direct box. The large 8 ohm resistor serves as a necessary dummy load for the tube amp. The unit can be built in a project box conveniently mounted to the console.