The old PH-1 has been replaced with the new PH-2. Like the new Rev E. Aikido PCBs, the PH-2 uses only polypropylene power-supply reservoir capacitors in its four power-supply RC filters. In addition, each channel's heater power supply connections are separate. And the new PCB is half an inch shorter (10.5 inches long). Although the circuit remains the same, two Aikido gain stages with passive RIAA equalization in between, the new boards are different enough from the PH-2 to warrant a new name.
Despite predictions to the contrary, spinning vinyl to the warm glow of vacuum tubes persists. In spite of the popularly— held belief that both LPs and tubes are dead, long dead— most believe that the vacuum tube died about 60 years ago and that the LP record died 38 years ago at the birth of the CD—both tubes and LPs grow more popular with each coming day. Tubes simply refuse to fade away and solid-state audio gear continues to be— embarrassingly— advertised as sounding tube-like; and turntables continue developed and sold and new records press on being pressed daily. Both tubes and LPs are here to stay.
Why do we need a phono preamp? The phono cartridge's minuscule output signal, being only millivolts, is too weak to drive a power amplifier, even with a line-stage amplifier's help; in addition, its output signal is not flat, as the signal coming off the LP's surface is not flat, having been equalized with boosted highs and attenuated lows. Thus, a phono preamp both amplifies and flattens the frequency response. In the Aikido PH-1, the first Aikido gain stage amplifies the cartridge's tiny output voltage and then passes the signal to the passive inverse RIAA equalization network, which boosts the lows and attenuates the highs, restoring a flat signal, but at the cost of an insertion loss of -20dB. The second Aikido gain stage then further amplifies the flat signal, bringing it up to a useable level. The final gain of the preamp can vary from 30dB to 48dB, depending on the tubes used. If a low-output moving-coil cartridge is used, then either a step-up transformer or a pre-preamp will be needed.
The Aikido PH-2 phono preamp is an extremely flexible design, as a nearly infinite number of different Aikido Phono Stage configurations can be built on the PCB. Nonetheless, our goals always remain constant: high-gain, low-noise, and low output impedance. The input tubes (V1, V5, V3, and V7) provide the voltage gain in this preamp, while the output tubes (V2, V6, V4, and V8) isolate the input tubes from both the equalization network and the external load, and they deliver a low output impedance.
Due to its symmetrical design and its forgoing of negative feedback, the Aikido gain stage is a great candidate for tube rolling. For example, a 12AX7 input tube can be replaced by a 12AT7, 12AY7, 5751, 5965, 6072, and even a 12AU7, without having to change any of the part values.
The usual tube line up is 12AX7, 12AT7, 12AX7, 12AT7. With these tubes, the gain comes in at over 40dB.
The Aikido PH-2 phono stage PCB requires an external power source for the B+ voltage and the two separate heater voltage supplies. The best choice is the PS-21, but even a well-designed non-regulated power supply will work well, such as the PS-15, as the PCB holds two cascading RC filters per channel to filter away ripple from the B+ connection.
The part kit holds all the capacitors, resistors, and tube sockets needed to populate the PCB, including 1kV polypropylene coupling caps and hand-matched RIAA equalization capacitors and polypropylene power-supply RC filter capacitors. The kit includes hex standoff assemblies with 1/2inch aluminum hex standoffs and O-rings and screws (9 sets) and a 16-page user guide.
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 traces, and the boards are made in the USA. The PH-2 PCB holds two Aikido phono-stage preamplifiers, with each phono preamp holding two Aikido gain stages with a passive RIAA equalization circuit in between. Thus, one board is all that is needed for stereo unbalanced use or two boards for balanced preamplification. The boards are six inches by eleven inches, with 12 mounting holes that help to prevent excessive PCB bending, while inserting and pulling tubes from their sockets.
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 (bulk-foil resistors and carbon-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.