The Tune Six is a fairly substantial component, borrowing the overall appearance and proportions of the company’s power amplifiers. Here, too, we find integrated but clearly visible heatsinks, along with side panels that can be easily removed and finished according to the user’s preferences. The same applies to the chassis as a whole.

In our case, the review sample came in a rather conservative black finish with wooden side panels (I insisted on a red finish, but here we are...). No great harm done, of course, because once the amplifier is switched on (using the touch-sensitive control in the center of the front panel), the first thing to catch your eye is the large touchscreen. It provides access to all the available functions and settings. From here, the user can adjust the volume, select the input, and configure the phono preamplifier, if one has been installed. One interesting feature is the option to adjust the volume in three broad ranges before making finer adjustments. This reduces the time required to set the desired level when starting from a very high attenuation setting.
The Tune Six can also be controlled using a conventional remote. It has a positive feel, but supports only the most basic functions: On/Off, input selection, volume, and mute. Alternatively, it can be operated over the home network, thanks to its built-in WebUI. To use this feature, the amplifier must be connected to the network; any device with a web browser can then access it and control all its functions. Both the on-screen interface and the WebUI allow the user to adjust the color and brightness of the graphics.

Connectivity is comprehensive. The amplifier provides four line-level inputs (single-ended/RCA), a preamplifier output and a recording output. If the corresponding modules are installed, these are supplemented by MM and MC phono inputs, as well as conventional digital inputs in the form of coaxial (RCA) and optical (Toslink) connections.
For data connectivity, there is an Ethernet port and three USB-A ports in total, one of which is located on the front panel beneath a magnetically attached cover. The same cover conceals the headphone output (6.35mm, TRS). The speakers connect via high-quality terminals.

Inside, the amplifier follows hARt Lab’s familiar design philosophy. The preamplifier stage uses two CV181 dual triodes. These tubes are available not only in matched pairs, helping to keep the two channels as closely balanced as possible, but also with their internal triodes matched. The circuit operates in Class A, without feedback, and drives the solid-state power stage directly, with no intervening driver stage. To minimize local negative feedback from the cathode bias resistor, LEDs (components with a stable forward voltage drop) are used at this point in the circuit.
The preamplifier’s attenuator is a stepped design with 64 steps of 1dB each, using relays and a topology that maintains a constant input impedance. The resistors are high-precision components optimized for audio applications. Input selection is also handled by relays, positioned close to the connectors.
The Tune Six’s power stage is a scaled-down version of the one used in the company’s power amplifiers, retaining their dual-mono architecture. It is based on MOSFETs, uses a symmetric topology, and operates in Class AB. The output devices are lateral MOSFETs from Exicon. One of their key characteristics is the close similarity between the complementary P- and N-channel devices, making them well suited to symmetric circuit designs.
The amplifier can accommodate two optional modules: the DAC-1, hARt’s D/A converter, and the Phono-1, which provides the preamplification and equalization required for moving-coil and moving-magnet cartridges. The DAC module is based on a digital interface/SRC and a Texas Instruments D/A converter chip (SRC4392 and PCM5122), and has its own regulated power supply. In addition to the conventional digital inputs, it includes an I2S connection to the SBC (Raspberry Pi) used for streaming. If the user chooses not to install the DAC, the streamer’s USB output must be connected to an external D/A converter, whose analogue output can then be routed to one of the Tune Six’s line inputs.
The streamer is controlled through the Volumio app, which the user can download free of charge to their device. The phono preamplifier is based on FETs operating in Class A, and features a passive equalization network. It has separate inputs for moving-magnet and moving-coil cartridges, offering gains of 40dB and 66dB, respectively, along with adjustable load for MC cartridges and input capacitance for MM cartridges.
As for the chassis construction, the company has once again followed their familiar approach. The outer enclosure is made from high-density fiberboard (HDF) and forms the shell beneath which separate structural components are housed. Their assembly incorporates damping material. The amplifier’s four support points are also very carefully designed, an important detail for a component weighing close to 30kg.

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