Fusion

Pronunciation: \ˈfyü-zhən\

Etymology: Latin fusion-, fusio, from fundere

Usage: A union by or as if by melting: as a merging of diverse, distinct, or separate elements into a unified whole
Fusion Amplifiers
Clearly, any form of using tube and solid state stages daisy chained in series cannot deliver what can be considered the best of both technologies without the sonic drawbacks.
The solution is as simple as it is ingenious. Instead of letting the tube section of the amplifier drive the solid state section of the amplifier, we let the tube amplifier drive the speaker. In order to “help out” the tube in delivering a lot of current we add a solid state power multiplier, which for every amount of current delivered by the tube adds many time the current.
The Tube amplifier provides all the Voltage gain and a certain amount of the total current to speaker.
The current multiplier can operate in Class AB. The crossover distortion from the class AB operation will simply be compensated by the speaker drawing more current from the tube amplifier section, which at the low levels around zero volt output voltage has fairly large current reserves.
The summing stage shown is a simple passive combiner which combines the currents from the (single ended) tube amplifier and the solid state current multiplier. It also sets the multiplication ratio.
Compared to the classic hybrid amplifiers the Fusion principle has one key draw back. We can no longer just use a simple small signal tube to drive the rest, we must provide a full Amplifier with the ability to provide appreciable power into the speaker.
However the benefits of the Fusion principle are clear and have been shown in repeated listening tests with amplifiers that allow the Fusion power multi. Other than adding extra power the fusion circuit has no appreciable sonic impact, preserving the original sound quality of the tube amplifier section completely intact.
Our first commercial uses a complete 300B Amplifier based on our Lux as the driving tube Amplifier, one can conceive easily other applications. With a small circuit change to adjust the power multiplication ratio for example one could use a single tube plus a transformer of a suitable ratio (perhaps the Russian 6S45 ‘supertube’ with a 4:1 line-output transformer) or perhaps a tube based headphone amplifier. Even a quite low powered OTL Amplifier may serve in the driving seat. The possible application are literally endless.

Download the attached pdf to get the whole story