No Gain, No Pain; No Hummer, No Bummer
Tube-based buffer line stages that provide no voltage gain are, surprisingly enough, rare. As far as I know, no commercially-offered, unity-gain, tube-based line-stage buffer exists. This is an odd situation, as passive line-stages are popular, which proves that extra signal gain isn’t always required. Additionally, the passive line- stage does not require plugging into the wall and it adds no extra active devices into signal path. It is the purest of the pure.
Yet passive line stages often prove inadequate, incapable of adequately driving high-capacitance cables or low-input impedances. Moreover, most active line-stage amplifiers can often impart the missing heft and solidity that are missing in many passive setups, even when the load is wimpy, but at the cost of greatly increased complexity and cost—and with some added noise and distortion.
The Aikido cathode follower PCB/kit, in contrast, is a modest affair, consisting of one tube per channel (two triodes per tube envelope) and a handful of capacitors and resistors. This unity-gain buffer, using a modified cathode follower, offers a high input impedance, a low output impedance, low distortion, and a great PSRR figure. In addition, the ACF does not invert the phase. The ACF use is not limited to line-stages, as the ACF can be used in creating an active crossover or even a headphone driver, if the headphone's impedance is high enough and the tube robust enough. On the other hand, the PCB can be configured for White cathode follower use.
Suitable tubes for the ACF are the 6BL7, 6BX7, 6SL7, 6H30pi, 6SN&, 12SN7, 12SX7, 12SL7, 5691, 5692, and ECC32. A PS-3 or PS-4 power supply would be perfect mate for the ACF.
Includes 12-page user guide. Part kit includes two 0.22µF and two 1µF 1kV CDE polypropylene coupling capacitors.