The Aikido PH-1 phono stage returns. Building phono stage based on the Aikido topology makes perfect sense, as the Aikido’s low distortion, noise, and output impedance, without the use of negative feedback—all are highly desirable attributes in a phono preamp.
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 35 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-1 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 Aikido PH-1 phono stage PCB requires an external power source for the B+ voltage and the heater voltage. The best choice is a well-regulated power supply, but even a well-designed non-regulated power supply will work well, as the PCB holds two cascading RC filters per channel to filter away ripple from the B+ connection. Ideally, the heaters will get a regulated DC power supply, as AC heater voltages will introduce too much hum. A good choice for the power supply is the GlassWare PS-1, which offers both regulated high-voltage and low-voltage outputs.
This kit includes all the capacitors (31), including four CDE 1kV polypropylene coupling caps and hand-matched RIAA equalization capacitors, PCB, resistors (with many redundant values), standoff assemblies with O-rings and screws (10), and ceramic tube sockets (8); sets of eight high-quality tubes are also available here. The Kit includes 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-1 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.
Multiple Heater Arrangements: The PH-1 PCB allows either 6.3V or 12.6V or 25.2V heater power supplies to be used and 6V tubes, such as the 6N1P, can be used with 12V tubes, such as the 12AU7.
Power-Supply-Decoupling Capacitors: PH-1 PCB provides space for four sets of capacitors to decouple each Aikido gain stage from the B+ connection. 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.
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.