The Aikido All-in-One 9-pin stereo PCB contains two Aikido gain stages and both the high-voltage and heater power supplies.
This FR-4 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. In addition, the PCB is lovingly and expensively made in the USA. The boards are 8 by 6 inches, with five mounting holes, which helps to prevent excessive PCB bending while inserting and pulling tubes from their sockets. The PCB holds two Aikido line-stage amplifiers; thus, one board is all that is needed for stereo unbalanced use (or one board for one channel of balanced amplification).
By including the necessary components for the heater and high voltage B+ power supplies on the PCB, the All in One board makes building a standard-setting line stage amplifier a breeze. This assembled board with a chassis, volume control, selector switch, power transformer, and a fistful of RCA jacks is all that is needed.
B+ and Heater Power Supplies On the All in One board, two power supplies reside, one for the high-voltage B+ for the tubes and a low-voltage power supply for the heaters. The high-voltage power supply uses an RC filter to smooth away ripple, while the low-voltage power supply uses an LDO voltage regulator to provide a stable and noise-free voltage output.
The Aikido All-in-One Noval PCB requires a traditional tube power transformer to energize its two power supplies and heat the rectifier, which requires its own 5Vac winding. The 6.3Vac winding that feeds heater power supply must offer at least 3.6 times more current than the heaters will draw. For example, four 12AU7s will draw 0.6A @12.6v, so the heater power transformer must be able to sustain an AC 2.16A current draw. A center-tapped secondary must be used and the its center-tap must be attached to CT eyelet. A good example is the Hammond 270CAX power transformer, which is perfect for powering four 12AU7 tubes.
Redundant Solder Pads
This board holds two sets of differently-spaced solder pads for each critical resistor, so that radial and axial resistors can easily be used (radial bulk-foil resistors and axial film resistors, for example). In addition, most capacitor locations find many redundant solder pads, so wildly differing-sized coupling capacitors can be placed neatly on the board, without excessively bending their leads.
Two Output-Stage Topologies
This PCB provides two output circuit configurations: the output stage can be configured either as the classic Aikido line amplifier or as an Aikido push-pull headphone amplifier. The standard Aikido is a thoroughly single-ended affair, nothing pulls while something else pushes. Unfortunately, wonderful as single-ended mode is sonically, it cannot provide the larger voltage and current swings that a push-pull output stage can. Single-ended stages can only deliver up to the idle current into a load, whereas class-A push-pull stages can deliver up to twice the idle current into the load. For a line stage, such big voltage and current swings are seldom required; headphones, on the other hand, do demand a lot more power; really, a 32-ohm load is brutally low impedance for any tube to drive. Fortunately, the PCB can be configured as an Aikido push-pull amplifier, which encompasses an optimal White cathode-follower stage, which will both retain the Aikido’s great PSRR and allow up to twice the idle current to be delivered into low-impedance loads.
The All in One PCB provides space for two sets of capacitors to decouple both Aikido gain stages from the B+ connection and each other. This arrangement allows a large-valued electrolytic capacitor and small-valued film capacitor to be used in parallel, while a series voltage-dropping resistor completes the RC filter. In place of the RC series resistor, an off-board choke can be used (one per channel).
The made in the USA PCB comes with 16-page user guide that holds schematic and design examples.