Sidebar 1: Relax and float downstream...
The Transnova idea is conceptually elegant and not dissimilar to a push-pull tube output stage. In a conventional output stage (diagram A), the "positive" or "hot" load terminal is connected to the junction between the emitters or sources of the complementary output transistors and the ground load terminal to the junction between the ±V reservoir capacitors. In general, this point defines the ground potential or 0V and is used as the amplifier's fundamental or "star" grounding reference. The output devices therefore act as emitter or source followers; they amplify current but their voltage gain is unity or less. The previous stages have therefore to provide all the amplifier's voltage gain as well as having sufficient output current ability to drive the output stage.
Diagram A conventional power amplifier output stage and power supply connections.
The Hafler, however, has the junction between the devices connected to ground, the drive to the load being taken from the junction between the capacitors (diagram B). You might think that nothing will happen, but the trick is that the common capacitor connection is not tied to ground, meaning that the power supply "floats" with respect to ground potential. When the output devices amplify the signal present on their gates, therefore, the entire power supply—capacitors, rectifiers, and transformer secondaries—is swung up and down by the FETs' sources. The common point is swept up and down with the power supply and therefore delivers current into the load. As the Transnova output FETS amplify both voltage and current, this greatly simplifies the task for the upstream circuitry.—John Atkinson
Diagram B Transnova output stage and power supply connections.
