A task for each one

The apparatus is made of two chassis. The inferior part has the power supply and all the control logic, including the amazing fluorescent display, while the upper part contains the stages of analog signal management. The choice is to optimize the complex circuitry by keeping electrically noisy parts far from those used in the signal. This preamplifier may be almost described as a three chassis apparatus because the line stages of two channels are completely separated on the power supply and ground level. Additionally, the logic part is separated with an insulated ground.

Zero ground-loop

The connection between logic and two stages is through photo couplers to guarantee the circuits separation. Thanks to this layout, we have the advantage to avoid ground loop. To this end, designers performed a further fineness: a complete electrical disconnection of all inputs, so that only the selected input is electrically connected to its line stage while all others are open including ground level.

This stubborn search, aiming to optimize ground tracks and avoid fussy ground loop brings inevitably to a redundancy of circuit series, mainly power supplies, thus bringing a considerable increase of costs. That is why it is impossible to find a similar solution in equipments of current production.

3 stage for signal

Signal management is then assigned to a hybrid circuit with three stages provided with a cascode differential for voltage amplification, where is applied to a double triode 6H30 and then two buffers; the first tube buffer with the second double triode 6H30 and the second with a mosfet tracker able to interface with the maximum outer world linearity. Two volume regulators per channel manage the balanced signal.

Volumes

The channels are solid state and are located inside two modules with rectangular shape fixed on the main printed circuit; the setting is on 168 steps of 0,5dB. A remarkable characteristic of this machine is the memory of set level on each input to avoid annoying volume changes when commutating from one input to another. Total amplification may be fixed at 0dB, +6dB or +12dB allowing to take full advantage of the sophisticated level regulators that permit the use of centre width and have a good resolution on the setting.

Power supply

Particular attention should be paid to the power supply unit and all parts located in the lower chassis of the machine. If opened, it gives the impression of seeing a power amplifier with a large amount of electronics. Two sides have power supplies of line stages; anodic voltage, voltage filaments (one per each tube), and voltages for analog stages of volume controls for each channel. The central part houses the power supply of the digital part, i.e. the microprocessor, relay, display and encoder. The fluorescent display is really a piece of art showing the useful information needed during functioning so that we can read the selected input, set attenuation and several other menu data (channels balance, input disabling, gain block of inputs, customization of inputsÕ

Symposium of power and fidelity

The monoblock delivers 200W of power on a load of 8 Ohm and uses a layout tested many times by Pathos. In fact, this is a balanced stage, which means that each amplifier is made of two power stages connected with INPOL configuration, intrinsically functioning in class A.

Hi-End Gotha

We would like to underscore that an INPOL stage can work only in class A. It is neither a push-pull circuit (where it is possible to choose how deep to polarize the final stage during the phase of design), nor a single-ended stage; considering the presence of a reactive element that works in symbiosis with an active device (in this case a group of mosfets connected at common drain). INPOL represents an alternative between the two configurations; hence, this topology created and patented by Pathos has properly gained by now its place in the Gotha of Hi-End.

Engineering art

This power buffer with unitary gain, is controlled by a tube amplification stage using three double triodes, two ECC83/12AX7 and one 6H30. The first stage generates voltage amplification based on differential totem pole with two12AX7. The second is a buffer with a common anode with the 6H30 that has the function of driving two groups of power mosfets. The signal on the two outputs amplified and out of phase between them, is delivered to two buffers with INPOL technology.

We have created a very powerful, extremely linear amplifier without using global feedback. It¡¯s difficult to describe the sizing of this apparatus power part; you should see it to fully understand the creativity of Pathos technicians and designers (as if we try to describe the Missouri battleship!).

The polarization of the two power stages is at a very high level: it allows a delivery of constant electrical current to avoid interface problems with diffusers. In this machine, technicians will find a series of outstanding details in the sophistication of the design. Starting from a power supply (completely stabilized for the signal stages on anodic voltage) that has a built-in C-multiplier in order to obtain the maximum filtering, on the voltage current generators and on the ignition voltage of filaments, usually considered less noble (but not by Pathos). The main important feature that distinguishes this project is the sensitive power supply that has to deliver a continuous electrical current of more than 12 A. Because the amplifier is at zero feedback, is necessary to use power supplies, filtered, in order to avoid hum noise in the output. Pathos, as usual, did not care about the cost of components and has used an optimum inductive/capacitive switching power supply able to perfectly filter the electrical current of the two power stages (for instance - the weight of filter reactance is 12 Kg).