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Aikido Pre-amp Kit

This was the third incarnation of the Basie Vacuum Tube Pre-amplifier from Diy HiFi Supply and it went through a complete re-design both in looks and the circuit it uses. The new circuit was based on John Broskie's famous Aikido design of TubeCAD fame. John kindly gave permission for his circuit to be used in this new kit. John is clearly a talented tube circuit designer, there are not many these days. I certainly don't claim to be. I just build kits and other peoples ideas :)

 

Design Changes

The style and layout of this Basie was completely different to the previous Basie kits. The Basie Mk1 and Mk2 kits had traditional manual selector switches, Alps volume pot and a metal chassis with all the tube sockets mounted directly on the top of the chassis. This meant that you would remove the base of the kit to gain access to the inside and all assembly took place with the unit upside down and bottom removed. This new unit uses all electronic control with push buttons for input selection and up / down buttons for the volume control. The unit is fully remote control capable and comes supplied with a basic remote. The input switching is now performed by miniature relays at the back of the unit and the volume control is a motorised stepped attenuator.

This new design does have several advantages over a classic non-remote design but not everyone will like it, especially if you are a traditionalist. Obvious advantages are the higher quality stepped attenuator as shown below and much shorter signal wires from the input / output sockets to the relay board. Other improvements over the older Basie include a non magnetic chassis and depending on your tastes a sleeker more modern style.

 

Build

The circuit can be built in 2 ways, the original John Broskie's Aikido design and an alternative experimenter gome's version. I built it using the original Aikido design. The standard circuit does have quite a few parts to fit and it can look a real nest of components once complete. Technically it is generally better to have a 'rats nest' style build with components at various angles and orientations rather than try and keep them all nice and neat in line which you find on some PCB builds. This method keeps components legs shorter, solder points closer together and minimizes noise and RFI interaction between components.

The main circuit is assembled on the plinth as a separate process from the the rest of the kit. The chassis requires signal input and output wiring to and from the RCA sockets and relays, volume pot signal wiring, HT supply wiring from the front power supply PCB and heater wiring. The problem occurs when the plinth and now completed circuit needs to be installed back in the case on the 4 pillars. Because the circuit is now face down it is not possible to solder any of the signal wires and supply wires from the chassis direct to the circuit were required. Instead you must measure the length of the wires needed from the circuit to each point in the chassis first, making note of any routing requirements, and solder these to the circuit side first before installing the plinth. Once the plinth has been installed these unconnected 'flying wires' can then be soldered in place at the various required chassis points. This then gives rise to another other problem. Once everything is fitted and soldered in place it makes it difficult to take any live measurements on the circuit. Also if you want to tweak and make changes, such as capacitor upgrades for example, you cannot just simply unsolder the part you need since the plinth needs to be unscrewed and turned upside down first which the circuit to chassis wiring can prevent if they are optimum shortest lengths. The only solution is to make the wires from the main circuit to the chassis points a little longer than required to give some slack to turn the plinth upside down, or at least on its side, when fitted. Otherwise you would need to un-solder the HT wiring, heater wiring and signal wiring to remove the plinth. This is were the classic Basie Pre-amp design was much better IMHO. It was far more DIY and 'tweaker' friendly.
 

Testing

I tested the Aikido on 3 different amplifiers and setup's. The first was my own Korsun v6i transistor amplifier. This is highly sensitive on its power amp input so can reveal and amplify any small amount of noise at the pre-amp stage. This showed up a few problems noise-wise such as hum and some high frequency oscillation. The high frequency noise was cured by increasing the size of the 100R grid stopper resistors to 1K and after some time fiddling with various wire routing and connections the hum was reduced to a low level. If it can pass my Korsun test noise-wise then it would be virtually silent on a tube power amplifier and dead silent on a single ended power amp which tend to be a little deaf on their inputs. A further mod was to cut one of the tracks on the HT power supply PCB and add a small value wire-wound resistor as shown in the new PSU schematic, anything 50 to 200R should be ok. This made the unit even quieter since it created another C-R-C stage. This PSU mod and wire routing layouts were eventually included in the Basie manual.
 

Sound

Ok, back to the testing with the Korsun / Dussun. On this transistor amplifier the Aikido was not a good match sonically. It had too much gain and did not really bring any kind of tube warmth to the sound. What struck me though was how fast, controlled and powerful the Aikido sounded. This was not really needed on this transistor amplifier. Many transistor amps tend to sound this way most of the time anyway. IMHO the ideal match for a transistor amplifier is a tube based pre-amp that has some warmth, tube colouration, bloom and richness etc. This complements the faster, colder more sterile sound of solid state amps and works really well. An alternative is to match a solid state pre-amp with a tube power amp.

Changing tube types does tailor the sound of the Aikido to give a better match sonically and if the 6CG7 input tubes are changed to a low MU type such as the 6N6P the gain could be dropped significantly making partnering the Aikido with a solid state power amp a more viable option. Testing it with a 845 SET integrated was much more successful. The Aikido displayed its sense of speed and timing again. Furthermore, the bass took on more slam, depth and control. A worthwhile improvement. It was more entertaining to listen to with the pre-amp than without it but it was not a day and night change.

The final test was at a Friends house with his Russian push-pull tube amplifier and Martin Logan's. This was a day and night change. A major improvement over his TVC pre-amp. The same Aikido speed and timing was present but it also brought a big improvement throughout the entire soundstage. It was incredibly dynamic, alive and spacious sounding.

 

Summary

In summary, the Aikido circuit sounds amazingly dynamic and fast, esp in the right combination of power amp and speakers, not at all full of bloom and softening of leading edges. If your system sounds too laid back and you want to inject some life then this is a great circuit and build. However, if you want a tube pre-amp with lots of bloom and a fatter rounded warm tube like sound then the Aikido may not suit in its standard build. You would need to assemble it to use one of the many other tube types it can utilize. This is quite a list of tubes so tailoring the sound would not be a problem.

What the Aikido has though is a sense of pace and timing. It is very fast which is rare for a tube amplifier. Bass has depth, attack and slam, mid-range is focused but not forced or forward, treble is typically tube like being sweet and clean but it also is very extended like the best solid state pre-amps. In the right system this amplifier can bring the entire soundstage to life as I found out.

 

Schematic-Aikido-Psu
Schematic-Aikido-Pre
Schematic-Aikido-Gomes
Aikido-Pre-5
Aikido-Pre-4
Aikido-Pre-3
Aikido-Pre-2
Aikido-Pre-1


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