The Design Of The Amplification Stages
The Preamplifier Stage
Two Burr-Brown OPA 2134 SoundPlus™ operational amplifiers provide the pre-amplification. These are specially designed for audiophile circuits and are characterized by extremely low noise and minimal distortion of only 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.
In addition, 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.
The excellent Panasonic ‘Electric Double Layer’ gold electrolytic capacitors are used as coupling capacitors. They offer the highest storage capacity of all capacitor technologies.
The Power Amplifier
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.
in the headphone amplifier is the Phonitor Matrix, with adjustable crossfeed, thanks to which you can create mixes with headphones that sound the same on speakers.
The Phonitor Matrix in its largest expansion stage has three setting parameters: Crossfeed, Speaker Angle and Center Level.
In the Phonitor One d, the center level is preset to -1 dB and the speaker angle to 30°. These are the most commonly used values.
The crossfeed function 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.
Three Stereo Inputs
Two analog stereo inputs and one digital USB input can be connected to Phonitor One d. The computer, tablet or phone are preferably connected via USB.
Other players such as a CD player, mixer, synthesizer or an analog tape machine / tape deck can be connected to the analog line inputs either balanced (TRS jacks) or unbalanced (RCA).
The converter chip used is the Premium AK4490, a new generation of premium 32-bit DACs equipped with AKM’s Velvet Sound®. This technology makes the finest details audible thanks to its low-distortion architecture.
It supports sampling frequencies up to 768kHz PCM (16x CD resolution) and DSD (Direct Stream Digital) playback up to DSD4 or DSD256 (11.2 MHz) resolution.
This qualifies the Phonitor One d for the currently highest resolution audio playback.
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 at the bottom of this page.
The selected input signal is output unchanged at the line out. This allows Phonitor One d to be looped between devices without “losing” an output connection.
If, for example, several people are to listen in via headphones, a headphone amplifier can simply be connected to the Line Out.
But you can also record the signal analog or send it to a mixer for further processing.
Thus, the Phonitor One d can also be used as a state-of-the-art DA-converter, which recommends it for a series of other tasks.
The Power Supply
Good sound always starts with the power supply. This is where you lay the foundation for the performance of the entire device.
Although we “only” supply a 12 V plug-in power supply unit, the secondary power supply inside generates a voltage level of +/-17 Volts for the analog audio sections with which professional levels of up to +22.5 dB can be achieved!
An elaborate low-drop operating voltage regulation provides more “juice” and regulates cleanly even when the maximum operation voltage is reached.
The Phonitor One d delivers full power when used with the included 1.5 A power supply. Only use the 12 V plug-in power supply unit within the scope of delivery. The ON-switch puts the Phonitor One d into operation.