Posted on Saturday, 4th October 2008 by Auw Jimmy
Well, I have one week holiday and I’m almost dead because of doing nothing. Since I have a pair of Aikido 9-pin Preamp PCB, why don’t I build one?
The main concern of this project is simplicity and cheap price. I don’t want to spend too much money for this project (just to kill my boring days).
So here is the PCB. Nice, sweet, well build by John Broskie.
The first thing that I do (after finding the component from my shelves) is to clean up the connectors of each component. By using a scissors, I clean up the component leads.
As you can see, the green box is a clean connector, while the red box is not yet cleaned part. By the way, I use cheap NOS Vishay L6C Metal Film resistor. Although it’s looked awful physically, but the value is still good.
I also test one by one. With my Ohm Meter, 1 MOhm resistor measured at 1016 KOhm. Hmm, 1.6% drift value seemed ok.
Then I start to put the components on the PCB and start the soldering process. I start with the smallest and shortest components first.
My tools, WBT Silver Solder and Goot soldering iron.
I also need to replace R15 with a jumper (because I configure this Aikido as White Cathode Follower). I use the lead from some component that I’ve finished soldering. I also wrap the jumper lead with WBT silver solder to prevent any corrosion in the future.
I also use old stock Vishay S139 resistor as output shunt resistor (just because I only have this resistor with 10-11 KOhm value). This is a damn good resistor at 0.01% tolerance. As you can see, the 11 KOhm value is 11 KOhm measured with my Ohm Meter.
For some mistake in soldering, I will use my Goot Solderwick to remove the wrong component. This is a clean and perfect way of desoldering process.
Well, two PCB are done! You can see some affordable components like Elna Cerafine, WIMA, Russian K72 Teflon and K40Y PIO, and Obbligato capacitors.
Another shoot from the top side. Beautiful color combination, isn’t it?
Some combination of resistor, from the Vishay S139, Kiwame, Vishay L6C, and Dale. The two K40Y capacitors are used for grounding the tube screen pin.
I have added the power supply board and also the attenuator board.
The power supply is a simple one, choke loaded (15H), two Samhwa 220uF/500VDC capacitors, and a tube rectifier with Russian 5U4C.
Another side of the power supply board. I use 1.5mm power supply cable. Thick, eh?
Since this Preamp will also act as my headphone amplifier, then I need to have a big coupling capacitor to drive my 32 Ohm Grado. I use Mundorf M-Lytic 560uF/400VDC. This should be enough to give high pass filter at 8.88 Hz at 32 Ohm load. The attenuator is ALPS 100K motorized potentiometer.
I ask my friend to build custom power transformer.
- The primary is 0-220V
- The secondary is 300V-CT-300V (100mA), 3.25V-CT-3.25V (3A), and 0-5.25V (3A)
Well, the Preamp is singing now. I use 6N1P and 6N6P tubes and 5U4C as rectifier.
The “giant” 6N6P. The combination of 6N1P in gain stage and 6N6P in buffer stage produces a perfect combination here.
I hear a B+ hum when testing. Then, I decide to add a neon ballast acting like a choke. So the power supply configuration is “Transformer-ChokeLoaded-Capacitor-NeonBallast-Capacitor”. This is a “poor” solution if you don’t have any extra choke and quite effective! No more hum, baby! You also can see a high voltage switch and how big the transformer is!
Add: I replace the Neon Ballast later with a choke (and produce even lower hum on my testing).
One shoot of the Aikido with 5U4C rectifier. Good performance rectifier with its price range.
A final shoot of my Aikido Preamp. I replace the 5U4C tube with 5U3C/5U4GB Sylvania Black Plate rectifier. It sounds even better in resolution and clarity. Overall, I’m quite satisfied with this as my holiday project. Will try to find a good chassis and mount it inside.