SPL are the initials usually associated with the term sound pressure level, but it is also short for Sound Performance Lab, a German firm that has been making professional recording gear since the late 1970s. Founded by Wolfgang Neumann, SPL grew out of the needs of his own professional studio, which was located near the Dutch border. After a few years Neumann sold the studio and began manufacturing pro gear full-time under the name SPL.
Since the early 80s SPL has been actively involved in building high-performance professional recording equipment under its own name as well as manufacturing OEM products for Sennheiser, Genelec, Terratek, and MB Quart. Among SPL’s own branded offerings are monitor controllers, interfaces, preamplifiers, compressors, power amplifiers, speaker simulators, and headphone amplifiers. We are going to look at one of its headphone amps, the Phonitor X.
The Phonitor X is part of SPL’s latest line of “pro-fi” gear, which bridges the gap between the professional and consumer markets. The Phonitor X is similar to SPL’s Phonitor II professional headphone amplifier, but with several features removed that were primarily of use to pros and with the addition of some controls that make it more user-friendly for consumers, including an optional DAC section.
The principal technical feature that separates the SPL Phonitor X from its competition is SPL’s 120-volt rail technology that reportedly reduces distortion and has an electric measurement the company claims is “four times as high as in standard audio designs,” which are typically around 30 volts. “THD measurements of the 120V op-amp show a difference of more than 3dB compared to the OPA134 at 36V—in sound pressure level, that corresponds to an improvement of more than 50%.” The first generation of SPL’s 120V amplifier circuit premiered in 1998 and was utilized until 2009. Since then SPL has gone through four more iterations, culminating in its latest balanced I/O driver first produced in 2013.
With balanced and unbalanced headphone outputs on the front panel and balanced and unbalanced line-level outputs on the back panel, the Phonitor X can serve as a preamplifier as well as a headphone amplifier. Maximum output is 3.7 watts into 120 ohms, but you can change the output settings via a series of dipswitches on the bottom of the unit. You can boost the factory default headphone output by either 12 or 22dB. You can also set up the Phonitor X so that a chosen input will go directly to the RCA or XLR outputs on the back without attenuation from the volume control.
On the back panel there is space for the optional DAC card. It was not yet in production when I received the Phonitor X, so I could not put it through its paces. That will have to wait for a follow-up. The card will utilize the AK4396 DAC chip and the current specification lists it as 192/24 capable. The chip can even support DSD, but as of now that is not included in its feature set, though it could be added via a firmware upgrade at a later time, depending on feedback from customers.