Aikido Octal Stereo Rev F
This is a major new revision of the old Aikido stereo octal PCB, Rev. F. The PCB color is now red, but the real difference is found in two major changes: each channel's B+ RC filter is made up of pure polypropylene (no electrolytic) capacitance and each channel requires its own separate heater power supply. The red solder-mask merely marks these changes and looks quite snazzy by itself.
All that is needed to finish the entire line stage is a chassis, power supply, volume and input selector controls, and a handful of RCA jacks and hookup wire. Although this custom Aikido kit isn't all that is needed, it is a great start.
The PS-21 is the same width as the new Aikido Octal, so it can be placed right up against the new board. The PS-21 three regulated power supplies: one high-voltage and two separate low-voltage regulators.
WHAT IS AN AIKIDO AMPLIFIER?
The Aikido tube topology, created by John Broskie, delivers the sonic goods.
Since the Aikido circuit came out in the Tube CAD Journal (http://www.tubecad.com/2004/blog0011.htm ), people have been building it and marveling at its sound. A prediction: just as the 1980s were the cascode decade and the 1990s, the SRPP decade, this decade will be known as the Aikido decade.
This amplifier circuit offers voltage gain, low distortion, low output impedance, and a high PSRR figure—all without a global feedback loop.
Better than SRPP or Grounded-Cathode Amplifier
The Aikido circuit symmetrically balances imperfect triodes against equally imperfect triodes, which greatly reduces its distortion output; it also sidesteps power supply noise by incorporating the noise into its normal operation. As a result, in terms of distortion, output impedance and PSRR, the Aikido circuit works at least a magnitude better than the equivalent SRPP or grounded-cathode amplifier. The improved PSRR advantage is significant, greatly unburdening the power-supply.
Yet noise reduction is only half of the Aikido’s virtues—this circuit’s flexibility really makes it shine. Different input and different output tubes can be easily interchanged, as long as they have the same socket pin-out and heater voltages. Because the circuit uses symmetrical triodes in place of plate and cathode resistors, a 6BL7, 6BX7, 6SL7, 6SN7, 12SL7, 12SN7, 12SX7, B65, and ECC32 could be interchangeably used in an Aikido amplifier ostensibly designed around the 6SN7.
Always Biases Up Correctly
A fresh triode is not the same as that same triode after 2,000 hours of use. Remember, tubes are not stainless steel yardsticks, being more like car tires—they wear out. Just as a tire’s weight and diameter decrease over time, so does a tube’s conductance. But as long as the two internal triodes age in the same way—which they are inclined to do, as they do the same amount of work and share the same materials and environment—the Aikido amplifier will always bias up correctly, splitting the B+ voltage between the triodes.
Functions Flawlessly Despite Wall-Voltage Swings
Additionally, unless regulated power supplies are used for the B+ and heater, these voltages will vary at the whim of the power company and your house’s and neighbors’ house’s use, usually throwing the once fixed voltage relationships askew. Nevertheless, the Aikido amplifier will still function flawlessly, as it tracks these voltage changes symmetrically.
No Popping Sounds at Startup, No Squirrelliness
Moreover, the Aikido amplifier does not make huge popping swings at startup, as the output does not start at the B+ and then swing down a hundred or so volts when the tube heats up, as it does in a ground-cathode amplifier. Furthermore, the Aikido amplifier seems to bypass much of the power supply squirrelliness, making the circuit sound as if it were attached to batteries or a well-regulated power supply.
Most importantly, the circuit produces far less distortion than comparable circuits. The triode is not nearly as linear as a resistor, so ideally, it should not see a linear load, but a corresponding non-linear load. An analogy is found in someone needing glasses; if the eyes were perfect, then perfectly flat (perfectly linear) lenses would be needed, whereas imperfect eyes need counterbalancing lenses (non-linear) to see straight. In other words, loading a triode with the same type of triode works to flatten the transfer curve of the amplifier.
A Sound that’s Hard to Improve Upon
So, in sum, we get quite a bargain in the Aikido amplifier: low noise, low distortion, low output impedance, and no global feedback loop. The result of all these features is an effortless, clean, and natural sound that is hard to improve upon.
AIKIDO AMPLIFIER PCB
Some have simply hardwired their own, while a few have started producing unofficial Aikido PCBs for sale. Many of you requested a genuine GlassWare Aikido PCB, and this is it. This one was designed by John Broskie himself for you, the Tube CAD Journal reader.
What makes them superior? First of all, they look fabulous and feel solid in the hand: extra thick (inserting and pulling tubes from their sockets won’t bend or break this board), double-sided, with 2oz copper traces, clean silkscreen and solder mask. (The board holds two sets of differently spaced solder pads for each resistor, so that radial and axial resistors can be easily used. Each capacitor finds several solder pads, so wildly differing sized coupling capacitors can neatly be placed on the board.) Each board holds two Aikido linestage amplifiers; so, one board for stereo unbalanced or one board for one channel of balanced amplification.
The boards hold two coupling capacitors, each finding its own 1M resistor to ground. The idea here is that you can select (via a rotary switch) between C3a or C3b or both capacitors in parallel. Why? One coupling capacitor can be Teflon and the other oil, or polypropylene or wax and paper…. As they used to sing in a candy bar commercial: “Sometimes you feel like a nut; sometimes you don't.” each type of capacitor has its virtues and failings. So, use one type of coupling capacitors for old Frank Sinatra recordings and the other for string quartets. Or the same flavor capacitor can fill both spots: one capacitor would set a low-frequency cutoff of 80Hz for background or late night listening; the other capacitor, 5Hz for full range listening. Or if you have found the perfect type of coupling capacitor, the two capacitors could be hardwired together on the PCB, one acting as a bypass capacitor for the other.
The Aikido Octal stereo 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. The boards are 6.5 by 6.3 inches, with five mounting holes, which helps to prevent excessive PCB bending while inserting and pulling tubes from their sockets.
This latest Aikido PCB does incorporate a few small improvements, such as the two output coupling capacitors (which I deem essential) and the ability to be configured as an Aikido Push-Pull circuit, which is perfect for those wishing to build a tube headphone amplifier for high-impedance cans. Of course, the Aikido Octal stereo board is not limited to this one application by any means. Line stages, single-ended power amplifier front-ends, tube-based mixers, I-to-V converters—all are possible with this Aikido PCB.
PCB includes 16-page user guide with schematics and instructions.