Introducing the new Aikido 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.
Where the typical tube-based line-stage amplifier requires a B+ of 200V to 400V, the Aikido 12Vac can get by with only a B+ voltage of 80Vdc with 6DJ8/6922/E88CC tubes; or 120Vdc with 12AU7/ECC82/ECC802 tubes. The heaters are all placed in series and this heater string is powered by a portion of the the B+ power-supply voltage, the center third. Thus, a wallart's low-voltage AC from is all that is required to power the Aikido 12Vac.
The power supply is internal to the 12Vac Aikido 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.
If instead of a 12Vac wallwart an 18Vac input voltage is used, a raw DC voltage of about 148Vdc is created. The 92Vdc voltage is perfect for use with four 6DJ8 tubes; the 148Vdc, with four 12AU7 tubes. The 12Vac transformer used with 6DJ8 tubes must provide at least 1.5A of current, which equals a VA rating of 18; the 18Vac transformer used with 12AU7 tubes must provide at least 1A of current, which equals a VA rating of 18.
The Aikido 12Vac board holds stereo Aikido line amplifiers. If somehow you don't know what the Aikido circuit is, say Google dumped you here for the first time, the quick answer is that the Aikido tube circuit provides low distortion, low output impedance, and stellar PSRR (power supply rejection ratio)—all without the use of a negative feedback loop. It is both simple and effective.
The Aikido circuit delivers roughly a gain equal to half of the mu (amplification factor) of the triode used. With four 6DJ8 tubes (all the tubes must share the same heater voltage and heater current draw), the signal gain equals about 16 or +15dB; with four 12AU7 tubes, 8 or +9dB. This may not seem like much gain, but it is plenty for line-stage use, as most power amplifier require only 1Vpk to be brought to full output.
The Aikido 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, Wima, Nichicon, Panasonic. The optional A3 Mini Attenuator is an interesting design: a hybrid attenuator that uses both series and ladder attenuators to yield the best compromise between flexibility, performance, and cost. The A3 Mini uses three 6-position rotary switches to yield a total of 36 positions of attenuation in -1dB (or -2db) resolution.
Includes 16-page user guide with schematics and instructions.