The Phonitor One d from SPL is a headphone amplifier that offers an audiophile-grade performance to listeners and professionals alike.
Because of its pristine preamp, powerful headphone amplifier, and ability to handle high-quality PCM/DoP, the unit is suitable for those who enjoy high-quality critical listening, such as the audiophile, who might spin a record to unwind at the end of the day. However, because of its 32-bit DAC and dedicated stereo line outputs, the unit is also beneficial to professional engineers who need a high-quality monitoring path.
Whoever you are, you can make connections to the unit via balanced 1/4", unbalanced RCA, or USB connections. An input selector lets you switch among the three sources, and you'll also note the Crossfeed knob. This engages the Phonitor Matrix, SPL's technology for emulating speaker positioning within a room, all in your headphones. With the Crossfeed knob, you can dial in subtle amounts of the opposing channel to emulate the feeling of speakers. Mixing engineers might find this feature particularly handy when mixing in headphones.
The headphone amp itself utilizes a Class AB design, and is able to power both high- and low-impedance headphones alike. You can go between your favorite consumer-grade closed-back headphones and your high-grade open-backs without a problem. A 12V external power supply unit is included.
3 Stereo Inputs
Two analog stereo inputs and one digital USB input can be connected to the Phonitor One d. Your computer, tablet, or phone can be connected via USB. Other players such as a CD player, mixer, synthesizer, tape machine, tape deck, and more can be connected to the analog line inputs, either through balanced TRS jacks or unbalanced RCA connections
The converter chip used is the AKM AK4490, a 32-bit DAC equipped with AKM's Velvet Sound. This technology achieves a greater degree of resolution thanks to its low-distortion architecture. It supports sampling frequencies up to 768 kHz PCM (16x CD resolution) and DSD (Direct Stream Digital) playback up to DSD256 (11.2 MHz) resolution.
The USB connection is Class Compliant. This means that all Mac computers and iOS devices like iPads and iPhones can use the full performance bandwidth of the DA-converter without driver installation. iOS devices require the camera adapter. For Windows, a driver is required, which you can download freely from SPL.
Line Output Jack for DA Purposes
The selected input signal is output unchanged at the line out. This allows Phonitor One d to be looped between devices. If, for example, several people need to listen via headphones, a headphone amplifier can be connected to the Line Out without a noticeable drop in quality. You can also record the signal analog or send it to a mixer for further processing. Because of this line output, you can use the Phonitor One d as a high-quality DAC, as well as a headphone amp
Comprehensive Preamp Stage
Two Burr-Brown OPA 2134 SoundPlus operational amplifiers provide the pre-amplification. These are specially designed for audiophile circuits and are characterized by low noise and minimal distortion of 0.00008%. Thanks to a true FET stage, the OPA 2134 achieves a slew rate of 20V/µs, making it a high-speed operational amplifier. This has an immediate positive effect on the liveliness of the playback.
Additionally, low capacitance film capacitors are installed in the signal path as bypass capacitors of the coupling capacitors, which ensures a more precise transmission of the high-frequency signal components. Finally, the Panasonic 'Electric Double Layer' gold electrolytic capacitors are used as coupling capacitors.
Class AB Power Amp
The output stage of the headphone amplifier is designed as a push-pull amplifier in Class AB mode. The bipolar transistors share the amplification of the positive and negative half-waves, which produces a higher gain and a higher output voltage than in Class A operation, where only one transistor amplifies both half-waves.
The output stage transistors are thermally coupled and thus run particularly coherently, which contributes to a consistent and stable sound image.
The power supply has a buffer circuit with low source resistance, ensuring generous current reserves even when operating low-impedance headphones.
Adjustable Crossfeed for Stereo Speaker Sound
In the headphone amplifier is the Phonitor Matrix, with adjustable crossfeed, which you can use to recreate the feeling of speakers inside headphones. The Crossfeed knob determines the crosstalk of the channels, the so-called interaural level difference. The intensity of the crossfeed is fully variable.
At the beginning of the control path the function is not in the audio path. It is only switched on by adding it via relay (hysteresis circuit). The audio signal therefore does not pass through the crossfeed stage if this is not desired.