This past week we've had the privilege of having a noted designer in house working with us on a music server system. That is now up and making very nice sounds (more about that in another blog). It gave us the opportunity to set up the Fusion, listen and make some revisions by said designer.
I was impressed all over again. I've been using a Fusion at home for the last couple years but mostly casual but this week I've come to realize just how great this amp is at delivering in quantity true 300B sound through the MOSFET output stage. I was also reminded that I should have emphasized that the Fusion uses the same front end as the LUX (without the cathode choke).

OK here's the whole story:
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

HOT Fusion - the next generation of single ended amplifiers! The combination of pentode input, 300B output and no negative feedback add up to truly high end sound. The added "Fusion" Power makes any speaker compatibility issues a thing of the past. Fusion gives enough clean power and bass control to drive a pair of LS3/5 or ATC SCM7 to entertaining levels, with all the exceptional and legendary 300B sound quality intact!
Just need 10Watts? Run the amp with the Fusion Booster switched OUT for an exceptional 300B Amplifier. Want an instant 6db gain in available power to 40+ watts? Switch Fusion Booster IN. Dynamics are impressive, Fusion Boosted or not, as is openness and sound staging. Its performance belies its price many times over.

Detailed Description:

The 300B and driver portion of this amplifier derives directly from the exceptional Lux amplifier. The input gain stage is handled by an EF86 – the classic high gain/low microphonic pentode. Coupling is by one small high quality 0.015uf cap to paralleled sections of a dual triode 5687. The 5687 is direct coupled from the cathode to the 300B, providing a low impedance source to manage the 300B. This too is taken from the Lux, only the cathode choke is replaced by a high value resistive load with a large negative voltage supply. This passes all the speed, delicacy and finesse of the pentode music amplifier to the 300B wile improving drive and overload capacity immensely.

The 300B drives the speaker through the latest generation diyhifisupply output transformer, which is CNC wound for perfect lay, low capacitance and very wide power bandwidth and uses a high grade GOSS core. This provides the power output of around 10W, with matched speaker impedances of 4, 8 and 16 Ohm available. Then, flick the Fusion switch, and the power (of the 8 Ohm Tap) is now boosted to 40 watts into 8 Ohm and output impedance is reduced from 3 Ohm to 1 Ohm! You now have a 300B Amplifier that can handle any common HiFi and high end speaker well, not just high efficiency types!

The Fusion's "Power Booster" is not a simple solid state booster amp with tons of feedback as sold by some, nor is it a simple follower circuit found so frequently in hybrid amplifiers. Designed by a noted designer of single ended amplifiers, the fusion's unique "current dumper" circuit monitors the current provided by the 300B section to the speaker load and adds ten times the current provided by the 300B section. The 300B still drives the speaker through the output transformer and a high quality Kiwame resistor, from the 16 Ohm Tap. There is no negative feedback, no solid state buffers added after tube stage as in most hybrid amplifiers - just added current and much less load on the 300B so it delivers more voltage cleanly to the speaker. The 300B still directly controls the voltage and current applied to the speaker directly and interacts with the speaker.

With a 16 Ohm Speaker around 25 Watt are available, an 8 Ohm Speaker can draw on 40 Watt and a 4 Ohm speaker can rely on 65 Watt being available.

The Powersupply uses an over sized EI transformer with highly optimized choke filtered supplies. The large chassis and generous size dissipates heat evenly; it is normal for the chassis and power transformer cover to feel hot due to the efficiency of heat transfer from critical parts.

Did we mention the Fusion even looks good as well?

• Power output 300B only: 16 Ohm connection - 10W x 2 RMS @1khz < 5% THD 8 Ohm connection - 10W x 2 RMS @1khz < 5% THD 4 Ohm connection - 10W x 2 RMS @1khz < 5% THD
• Power output 300B + Fusion Booster (on the 8 Ohm connection only): 16 Ohm Load - 25W x 2 RMS @1khz < 5% THD 8 Ohm Load - 40W x 2 RMS @1khz < 5% THD 4 Ohm Load - 65W x 2 RMS @1khz < 5% THD
• Frequency response: 6Hz to 60KHz (-3dB@10W)
• Input sensitivity and impedance: 500mV, 100k ohm Output Impedance
• Speaker Taps 300B driven: 4 , 8 and 16 ohm
• Output noise: <1.5mv
• Power Consumption: 110/230V AC, +- 10%, 90W
• Control Functions: Front panel: Power On/Off, Top deck: Fusion in/out Input
• Interfaces: 1 groups (RCA) Output Interfaces: 4 Groups 4-way binding Post 0/4/8/16
• Vacuum tubes: EF86 x 2 or equivalent, 5687 x 2 or equivalent, 300B x 2
• Dimension (mm) and weight: 340(L) x 410(W) x 230(H), 28kg net
• Only available assembled