Introducing the new 12Vac SRPP PCB and part kits. The key advantage of the 12Vac SRPP 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 12Vac SRPP can get by with only a B+ voltage of 120Vdc. 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 SRPP PCB and receives its power from an external transformer, usually a 12Vac wallwart, which is not included in the part kit. The 12Vac voltage runs through an elaborate octupler circuit that develops both a high-voltage B+ and a DC heater voltage.
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.
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 2oz copper. The PCB is 3.6 inches by 6 inches, with four mounting holes, which prevents excessive PCB bending while inserting and pulling tubes from their sockets. The PCB holds two SRPP amplifier stages. Thus, one board is all that is needed for stereo unbalanced use or one board for one channel of balanced amplification.
Power-Supply RC Filters
Unlike the Aikido circuit, the SRPP offer a relatively poor
PSRR. Thus, the SRPP 12Vac PCB holds four cascaded RC (resistor-capacitor) filters to smooth away B+ voltage power-supply ripple. An additional RC filter cleans up the DC voltage that heater string sees. In addition, the heater’s RC filter prevents huge current inrushes through the heaters at start-up, when the heaters are cold and offer little resistance; this will extend the tube’s life.
Stereo SRPP Amplifiers
This board holds two SRPP line amplifiers. The SRPP circuit provides low distortion and the distinctive tube sound. The SRPP delivers roughly a gain equal to half the triode's amplification factor (mu). As the PCB is so small, it can be fitted into existing solid-state audio equipment, such as CD players, which are large empty. The SRPP can then be used to superimpose lush tube sound on otherwise cold-sounding gear.