New Aikido Octal Stereo Line-Amplifier Kit

Aikido Octal Stereo PCB
Aikido Octal Stereo PCB
Item# Octal Printed Circuit Board and User Guide
Vacuum Tubes:  Resistors for Aikido PCB with many redundant values:  HV Supporting Capacitors 400V or 200V:  Set of Ceramic PCB-Mount Tube Sockets:  Coupling Capacitors:  Audyn Coupling Capacitors for Headphones:  Sets of five PCB stand-offs and screws and o-rings:  Rotary switch & PCB for switching between output Capacitors:  Selector switch & PCB for switching between 3 input sources:  Super strong double sided tape to hold coupling capacitors in place: 
Availability: Usually ships in 2-3 business days

Product Description

Aikido Octal Stereo PCB
Design your own kit. If you already own many or none of the parts needed in building your own giant-killing Aikido line-stage amplifier, the above lists of parts will help you design an Aikido kit that includes everything you need to populate the PCB. Buy just what you need and save.

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.

What you see above is the new Octal Aikido stereo board. It's square not rectangular and does not hold a raw DC power supply, neither for the B+ nor for the heaters. No more All-in-One, in other words. Why no power supply portion? Simplest answer is that because no one size fits all. Some want to use an external power supply, some want fully-regulated high-voltage power supplies, some want many cascading RC filters and no regulation, some want only solid-state rectifiers, some want only vacuum-tube rectifiers, some want DC on the heaters, but no regulation, some want AC on the heaters... but all want the Aikido circuit.

The PS-14 is the same width as the new Aikido Octal, so it can be placed right up against the new board. From a few feet, with some squinting, the pair of PCBs would look identical to the old Octal All-in-One board.


The Aikido tube topology, created by John Broskie, delivers the sonic goods.

Since the Aikido circuit came out in the Tube CAD Journal ( ), 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.

Less Distortion

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.


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. In addition, the PCB is lovingly and expensively made in the USA. The boards are 6 by 6 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.


Four Tungsol 6SN7s
Four Tungsol 6SN7s
The old Tungsol name is back—as is much of the old glory. This new production 6SN7 from Russia is definitely an upgrade from the other 6SN7s in production. $80 for four Tunsol 6SN7s.
Four ceramic PCB-mount tube sockets
Four ceramic PCB-mount tube sockets
High-quality, PCB-mount, ceramic tube sockets work beautifully on the PCB. $10 for 4 sockets.