Introducing the new ACF 12Vac PCB and part kits. The key advantage of the Aikido 12Vac is that it can be operated from a lowly wallwart power supply, yet develop a fairly high-voltage B+ for the triodes and power the heaters with clean DC voltage.
The ACF12Vac board holds two unity-gain tube-based buffers that provide low distortion, low output impedance, and stellar PSRR (power supply rejection ratio)㻡ll without the use of a negative feedback loop. It is both simple and effective.
The ACF (Aikido Cathode Follower) circuit delivers roughly a gain slightly less unity. It can be used with either 12AU7 or 12BH7 or ECC99 tubes; no 6-volt-heater tubes, such as the 6CG7 or 6H30 or 6DJ8 can be used. This is the result of the 24Vdc of heater voltage created on the PCB from the 12Vac. Each heater element gets shunted by a 12V zener diode and its own 470µF/16V Panasonic FM bypass capacitor. The raw B+ comes in at about 90Vdc and is about 80Vdc after the RC filter.
Why would you need a unity-gain tube buffer? Although theoretically the purest path to follow, passive line stages often disappoint, proving inadequate and incapable of adequately driving high-capacitance cables or low-input impedances. In addition, many solid-state audio devices just sound too cold and brittle on their own. Adding a tube-based buffer can help humanize the sound, perhaps due to harmonic enrichment.
The power supply is internal to the 12Vac ACF PCB and receives its power from an external transformer, usually a 12Vac wallwart. The 12Vac voltage runs through an elaborate sextupler circuit that develops both a high-voltage B+ and a DC heater voltage. The sextupler creates a raw DC voltage of about 94Vdc from a 12Vac wallwart.
IMPORTANT: If a power jack is used to receive the AC voltage from the wallwart's power plug, it must be fully insulated, as the incoming AC voltage is referenced to half the raw B+ voltage. In other words, the plug's outer barrel must not be grounded. The easy solution is to use an insulated power jack.
The ACF 12Vac stereo PCB is extra thick, 0.094 inches (inserting and pulling tubes from their sockets won't bend or break this board), double-sided, with plated-through heavy 2oz copper traces and a part placement silkscreen on both sides. In addition, the PCB is lovingly and expensively made in the USA. The boards are 7 by 3.6 inches, with five mounting holes, which helps to prevent excessive PCB bending while inserting and pulling tubes from their sockets.
The part kits include all the parts needed to populate the PCB (including the coupling capacitors), except for the vacuum tubes. The parts are all high-quality and name brand, such as On-Semi, Nichicon, Panasonic. The CDE coupling capacitor upgrade is well worth the added cost, as these 1kV capacitors offer greatly improved sound.
Includes 16-page user guide with schematics and instructions.