Valve Hybrid Amplifier

Stephen W. Moore

Fostex High Efficiency Speakers

Fostex FE207E


I wanted to experiment with high-efficiency single-driver systems. Some adherents claim single-driver systems offer unparalleled transparency, especially in the frequency span of the human voice.

I chose the Fostex FE207E because of the driver’s versatility and overall good impression in the DIY community.


Using some Fostex construction plans, I built a pair of rear horn loaded enclosures, tested with (pictured) and without baffling.


Thus far, I have not discovered a way to make these sound good. I have also tried a vented box (pictured below with my EL84 monoblocks). The sound is dry, lifeless, and without any discernable soundstage.


After two enclosures (horn and vented), several amplifiers (solid state, hybrid, and valve), I have concluded that the Fostex FE207E sounds like crap.

Alternative Configuration

I also tried the Fostex FE207E in a vented enclosure with numerous amplifiers. Pictured is the development version of my EL84 push-pull amplifier.


I tried several solid-state amplifiers, including the Pass Zen (v4) amplifier and my Hybrid Aikido MOSFET amplifier.


The vented enclosure can be converted to a sealed enclosure by plugging the port and fine-tuning internal volume with inert material (bricks).


My conclusion is the FE207E behaves and sounds poorly—dry and lifeless.


Pass Zen v.4

Tube/MOSFET Hybrid

Fostex FE207E

EL84 Push Pull