Ole Lund Christensen

Christensen made his first mark in the audio industry by designing the highly acclaimed Focus and PUK recording studios in his native Denmark during the 1980s. Amplification followed almost by accident as he could not find units that met his expectations to power the integrated in-wall speaker installations he designed for these studios. As has happened before in the industry, this led to Christensen designing his own bespoke amplifiers. He later began manufacturing a domestic version of these amplifiers under the name SiriuS, and these received high praise in local audio magazines. In 1995 the SiriuS DM200 made its production debut as the world’s first ‘single MOSFET’ 200-watt per channel power amplifier.

Single MOSFET? I’ll let Christensen explain: “Single MOSFET here means that there was a single current path through one MOSFET only from the positive voltage, and another single MOSFET from the negative voltage in a push-pull amplifier. This meant that the task of measuring and selecting the many matching MOSFETs in parallel that normally share the current and power load was no longer required. Today several companies manufacture amplifiers using my unique MOSFET circuit, which uses just two driver stages, one for each MOSFET. This design removes the requirement for matching plus and minus MOSFETs, both MOSFETs being N-channel with no need for a P MOSFET whose data characteristics are inferior.”

Inside Christensen’s power amplifiers were some large capacitors in the power supply that few other companies ever use. “Nobody else seemed to want to pay the price” he says. “They’re hospital grade emergency backup quality capacitors. They are specified to 100kHz, whereas most large power capacitors are not high frequency devices.”

“I worked hard on making my power amplifier sound good even when it is clipping,” says Christensen. “In my recording studio days I learned the importance of nice-sounding