Steve Guttenberg says pro audio gear is "not really my bag," but he agreed to review an SPL preamp and power amp anyway. He ended up spending more listening time with them than with his own Pass Labs reference. SPL comes from the recording studio, and its hifi line borrows an idea from its mastering gear. Most audio circuits run on fairly low internal voltages, and a sudden loud peak can ask for more than they can give, which overloads them. SPL runs its circuits at several times the usual voltage, and since ordinary amplifier chips would be destroyed at that voltage, it designed its own from discrete parts. The result is extra headroom, the room a circuit has above the music's loudest moment, so its parts always work well inside their limits. Ian Dunmore of Headphones.com called the Phonitor x headphone amp "the proverbial wire with gain." SPL suits listeners who want a transparent sound with headroom to spare.

For headphones, start with the Phonitor x. SPL says the Phonitor se, x and xe share the same amplification, and the x adds outputs so it can also run a pair of powered speakers or a power amp. Dunmore never needed more than its lowest gain setting, even with Abyss and Audeze headphones. Try its Matrix controls, which send a little of each channel to the opposite ear as speakers do. Dunmore enjoyed them most with simple stereo-mic recordings of small-club jazz. The xe is the step up, and What Hi-Fi? gave it five stars for sound, build and features. For speakers, Guttenberg says he would buy the Elector preamp and add his own DAC. The Performer s900 power amp drove his Quad electrostats, a hard load, with more dynamics and bass impact than his Pass Labs amp. Aron Garrecht of SoundStage! Ultra found the Performer m1000 monoblocks "slightly warm yet powerful."

Hermann Gier told SoundStage! Talks how SPL began. His partner Wolfgang Neumann, a recording engineer, started the company in 1983 and had one of the earliest 24-track studios in his area. With the dollar worth about 3.5 marks, American studio gear was too expensive, so Neumann built his own. Gier, a bass player who needed a new bass preamp, met him in 1985 and joined him in 1986. Gier recalls that Neumann had read a Don Lancaster book saying two million filters were possible and perhaps 2,000 had ever been built. After two weeks of night sessions, at about two in the morning on February 18, 1988, they heard the sound behind the Vitalizer equalizer, which Gier says put SPL on the map. Dirk Sommer notes that SPL consoles are found in the studios of Bob Ludwig and Sterling Sound. Gier designed the Phonitor of 2008 so engineers could mix on headphones, and he says half of them went to hifi listeners. SPL has sold its Professional Fidelity line since 2016, with the same VU meters and toggle switches.