The Marc One from SPL is a monitor controller and 32-Bit AD/DA in SPL's One series of high-quality audio equipment. This unit offers two stereo inputs (one balanced, one unbalanced) as well as two speaker outputs, a headphone output, and a subwoofer output. As with the inputs, the output sections give you a choice of balanced or unbalanced 1/4" connection points. You'll also note the USB port, through which you can record or playback 32-bit audio at high sample rates.

Indeed, the Marc One can support PCM sample rates up to 768 kHz. If you have DSD audio you'd like to hear, you can play it via DSD over PCM (DoP) up to DSD256. Because this unit has line inputs as well as outputs, you can even record audio at these high sample rates and resolutions, which is great for capturing vinyl records or recording instruments such as analog synths. On its front panel, you'll find an input selector that lets you switch between your two line sources, which you can also blend, if that is your desire. An output selector allows you to choose between your A and B output sets. Another front-panel switch sums the stereo output to mono, which can be useful for checking the integrity of your mix. You can also swap the left and right channels in order to ensure that you're center elements are truly centered.

In the headphone section, 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-backs and your high-grade open backs without problem. A 12V external power supply unit is included.
2 Stereo Inputs
Two analog stereo inputs can be connected to the Marc One for sources such as a DA converter, CD player, mixing console, synthesizer, analog tape machine, tape deck, or more. You can also listen to a mix of your two sets of inputs.
Clean Line Output
The selected input signal is output unchanged at the Line Out. This allows the Marc One to be looped between devices. So if several people want to listen via headphones, a headphone amplifier can be connected to the Line Out. You can also record the signal or send it to a mixer for further processing.
32-Bit DA-Converter
The converter chip used is the Premium AK4490, a new generation of 32-bit DACs 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 DSD4 or DSD256 (11.2 MHz) resolution.
Three Monitoring Modes
Three monitoring modes are on hand. In the middle is the default setting "Stereo". To check the mono compatibility, set the switch to Mono. The third setting is a channel swap, which swaps the left and right channels. This is a great way to test if center elements are in fact sitting in the center of your mix, as you intended them. It's also an easy way to correct incorrect left/right orientation while viewing media.
Class Compliant USB
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.
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.