Aikido 12Vac line stage/pre-amp build & review

[MKG]

Stay tuned. I just placed my order.
I’ve got a Little Bear 6j1 pre in my system currently that is adequate but not quite doing it for me. I’ve also got a Douk 6p6p + 6j4, but it has way too much gain. Another AKer was kind enough to rework the schematic for me to make it more useable, and I bought all the bits to rewire it, but I decided it just wasn’t worth it. At least for now, it’s on the back burner.
I have high hopes for the Aikido. I bought everything that it requires direct from glassware/tubecad except for the tubes and a volume pot or stepped attenuator. My finances currently allow me to buy bits in stages, so the missing bits will be purchased the weekend after the next.

 

[mbz]

Careful consideration of the power supplies is need. Some people use relays/timers to get the start up and shut down
in the right sequence to avoid any nasty dc spikes. I've got one of the earler ones, yes sounds good but doesn't handle
sustantained bass (cello draw) very well. Got 2 other kits that I need to get back into...

 

[Lavane]

I've built 1Aikido preamp and later rebuilt it using different tubes. Recently I bought an Octal version. I was very happy with the first two using 9 pin tubes. The power supply is important. I used dual power supplies. One for B+ and the other for the heaters. Both used SS rectifiers and voltage regulators along with a thermistor for the B+ supply. None I have are a 12v version though. What are you going to use for a power supply? I'm not too familiar with the Glassware version. Can you get away with one of those brick supplies used for lap tops? After my first Aikido build I was hooked.

 

[MKG]

It’s built to be able to be run off of a 2amp 12v ac wall wart. I’ll probably end up picking up a potted toroidal transformer when I have the time to search for an appropriate one. I’ve read lots of glowing reviews about the aikido pre-amps, so I’m quite excited and have high hopes for the final outcome. It won’t look pretty- I’m all about function not form and I kinda like the look of my kits just bolted to a slab of wood, with shields sticking up where needed.

 

[Lavane]

I was impressed with the very first one. The thing was dead quiet. The sound was very clear. It didn't seem to color the sound at all.
What tubes does the one your building use?
The first one I built used 12au7's, then 12ax7's. The one I bought and I'm using now has 6sn7's.

 

[MKG]

At 12v ac it uses 6dj8 tubes, if you bump the voltage up to 18v ac it uses 12au7 tubes.
I haven’t decided on type or picked tubes yet, I tend to get myself in trouble there- I don’t have enough experience with tubes to know what appropriate substitutes are or what to look for in a tube. I always manage to end up buying at least one set that doesn’t work for my purposes. So I’m definitely open to suggestions, keeping in mind that I’m cheap.

 

[Lavane]

The RCA clear top 12au7's i used sounded really good. I'm using 6922's in my phono preamp and really like them as well. I'm going to try a set of 6dj8's next. I felt no need to add tone controls with the Aikido. All three had a very well balanced sound.

 

[MKG]

Thanks for the recommendation!
I’m thinking for now I’m gonna go with wall wart power supplies until I decide on the tube type I prefer, then I’ll get a 12v or 18v toroidal once I’m done fiddling with it.

 

[MKG]

My kit finally arrived. Apparently he was waiting on a few parts to arrived so there was a delay, so he tossed in a power jack and some cde caps. I’m not sure what’s so special about cde caps, but I’m guessing something or he wouldn’t have tossed them in to make up for the shipping delay.
I don’t know much about tubes- I tend to end up buying ones that I think are appropriate, finding out that they’re not, and then ordering more. I ordered a quad of amperex 6dj8 on eBay, hopefully they’ll work well.
I want to dive straight into the build but we have two mastiff-lab puppies coming on Sunday so we need to do some house prep. Mainly ripping the carpet out of the bedroom and installing some big ass dog safe and waterproof flooring, but since we’re redoing the flooring we’re going to paint as well while we’re at it. So... house work is going to take up most of my free time for the next month. Can’t really be mad about it even though I hate working on the house, because it means adorable fuzzy things are joining our family.
Anyhow, here’s the kit that I’ll build as soon as I have time.
It came in a flat rate box inside of a package, well packed and sorted. Nice thick pcb.

 

[MKG]

Made a little bit of progress.
I didn’t realize that this project required maths!
I’m at a stopping point until I figure out what value of resistors to use in what place.
I also decided to put this project in a proper enclosure instead of doing my usual “mount it on a random piece of wood”.
I think I bought a big enclosure to include both this and the Nixie tube vu meter kit that I have on the way. I’ll just need to cut and polish some plexiglass for the front panel to finish it off.

 

[Lavane]

I thought I bought a chassis big enough for my amp build and and the nixie meters. But when I measured out and marked the chassis plate today I realized the chassis is not quite wide enough for the nixie tubes.
What math are you having problems with? Is it just the resistors at the input? Or the power supply? I couldn't read all of the manual. Some was cut off.

 

[Lavane]

I use blue tape and cover the chassis. Then measure and mark everything. It's better than marking up the chassis. And if you mark the tape wrong you just peel and repeat.

 

[MKG]

I’m having issues figuring out what value to put in R2,4,8,11,12,13,15.
My kit came with multiple values for each.
The instructions have equations to determine each value, but I don’t understand the variables, for example- what the hell is mu? What is rp?
I emailed glassware for assistance.
My enclosure (hasn’t been delivered yet) measures 12.2” x 11.2” x 4.3” so I’m theory it should be more than large enough.

 

[Lavane]

MU is the amplification factor. RP?, regulated phase maybe? Glassware should be able to sort you out. I remember having two choices with a set of resistors with the board I used. It had to do with input sensitivity.

 

[Tom Bavis]

RP is plate resistance. Mu and RP depend on the tube, will be on the data sheet. For the 6DJ8, Mu=33 and RP = 2600 Ohms at 90V B+ as used by the Akido. The 12AU7 data sheet gives them at 100V and 250V, we'll use 100: Mu=20, RP=6500 Ohms.

 

[MKG]

RP is plate resistance. Mu and RP depend on the tube, will be on the data sheet. For the 6DJ8, Mu=33 and RP = 2600 Ohms at 90V B+ as used by the Akido. The 12AU7 data sheet gives them at 100V and 250V, we'll use 100: Mu=20, RP=6500 Ohms.

Thank you!

 

[MKG]

Case arrived. Back plate will be metal, front plate will be plexiglass so that I can see the tubes and guts and the Nixie tube peak/vu meter.
@Lavane, thanks for the painters tape trick- it’s already helping me with the layout and keeping me from having to drill multiple holes because my dumbass measured wrong.
Made some progress and essentially finished the board- but my heater & b+ voltages are reading too low even with the lowest rated resistors included in the kit. They’re gonna take a bit of tweaking. That or I need to turn my new-to-me variac up a tiny bit.

 

[Lavane]

Try using your multi meter and test the voltage at the output end of the variac. If it reads below 120v just bump it up a bit. Then test your B+ and heaters. I never rely on the little meter on my variac. It's looking good so far.

 

[MKG]

I checked it prior to connecting it to the Aikido and it was putting out an almost perfect 12.2 volts. ...but that was unloaded, I’m thinking I should maybe try bumping it up to 13.5. If that doesn’t get my b+ and heater voltages where they need to go then I’ll hafta order some lower value resistors (unless I happen to have some in my spares, but that’s not usually how this goes).

 

[MKG]

Bumped the unloaded voltage up to 13.4 and everything is measuring within appropriate tolerances.
Took a break to welcome two new family members, George & Gertie.
Decided to wire everything up to give it a listen (ungrounded and outside of case).
Something shorted out and threw a breaker at the box.
I have a feeling it may be the stepped attenuator- it didn’t work appropriately in my last project, I had hopes that it was just a wiring issue- gonna replace it with an alps pot.