With the chassis having near-standard dimensions (430mm wide and 410 deep), Tune Three is not dramatic size-wise. However, it is quite imposing through its overall aesthetics. The device housing is a very balanced mix of wood and metal, with the heat sinks visible and carefully finished. The overall finish is, also, of very high quality (glossy white lacquer in the case of the device we had for the review) with the side panels being removable so one can use materials and/or colors of their own choice.
If its dimensions are not impressive, given the kind of the device, weight is another matter. Tune Three weighs 32kg and calls for your attention both while in transport (the company will deliver it to you in a high-quality flight case) and when set up (you should find a robust surface with good ventilation). And don't forget to bend your knees while carrying the amp…

hARt has not left things to the usual standards when designing the simple Tune Three user interface. From the "Stand-By" mode (activated through a switch on the back), the amp goes to the "On" state via a touch-sensitive switch located at the center of the front panel, with the company logo being able to get any color the user chooses (through a pallet of 15 different colors) and whatever intensity suits him (adjustable to three levels). This allows a match between both the preamplifier and the panels to be used. The final result is as attractive as one would expect from a device in this price range.
Connectivity of the Tune Three is fairly standard, except for the absence of a balanced input pair (a justified choice, however, both by the structure of the circuit and the fact that both of the company's preamplifiers do not offer a balanced output). This means that the user has a single-ended (RCA) input and two pairs of binding posts to connect loudspeakers per channel, an option that facilitates the use of "heavy" cables (heavily shielded, or with a solid conductor or of a very large cross-section architecture, that is). All connectors used are of very good quality.

Inside the amplifier chassis, there are several interesting choices, as hARt has paid attention to every detail. The wooden housing, made of high-density fiberboard (HDF), is just a shell, under which there are three structural parts. The central is the amplifier itself (i.e the PCBs and the massive heat sinks. These are part of the chassis as two metallic sub-structures are attached to them, the first supporting the two transformers the connectors and the back panel) and the second supporting the touch-sensitive On/Off switch, the control circuits, and the front panel. Particular attention has been paid to attenuating the vibrations throughout the whole construction, including the four support points that use a unique material, especially suitable for isolation of external vibrations, in a structure the company calls FloatO.
Of course, the most interesting part of Tune Three is its circuit. hARt states that its evolution has taken place over fifteen years and that means it started long before the company entered the market. It uses a hybrid architecture, where a tube-based voltage amplifier stage (VAS) drives a semiconductor-based power stage. This approach is not unusual of course, but the similarities of Tune Three to your typical hybrid power amp end here. hARt Lab says that their goal was to bring the sound of a good tube circuit to an amp capable to drive difficult loudspeakers, where high power is required. The use of a semiconductor stage was, therefore, a one-way street, but hARt has chosen to pass the tube character up to the output, to create an amplifier with the corresponding sound but, also, with a top-class performance power-wise. So, in the VAS, Tune Three features a top-quality CV181 double-triode, a tube that is not only available in matching pairs (so that the two amplifier channels are as balanced as possible) but, also, in matching triodes inside each tube. The circuit is a class A design, without feedback and drives the power stage directly, without a driver stage. To minimize local negative feedback (from a cathode-biasing resistor that offers cathode degeneration -a local feedback approach) the circuit uses the light-biasing technique featuring LEDs that have a constant voltage drop.

The output stage is, in essence, a power buffer, with symmetric topology, biased to operate in AB class. It is based on four pairs of lateral technology MOSFETs per channel, from Exicon, a company specializing in audio-oriented power semiconductors. The lateral MOSFETs are, in a way, traditional for high-power audio applications. Hitachi's legendary 2SK135/2SJ50 complementary pair was of this type and became known because the P- and N- channel components were very similar in their basic characteristics, to support symmetric circuits. Exicon's components are even better in this area, which is a not at all negligible detail since the P- and N-channel MOSFET closeness is a key feature of a FET-based symmetrical power stage.
The amplifier is a dual mono design and features one heavy power supply per channel, which starts with its own, custom, toroidal transformer, uses high-speed rectifiers, and a main filter with two 47,000uF capacitors. The amplifier circuits are highly cared for, with local regulation (including a regulated voltage source for the tube heater), four 12,000uF capacitors for the low voltage part, and three 560uF capacitors for the high voltage part of the circuit, for each channel. The amplifier uses audio-grade passive components and the overall quality of the construction is very high.