February 21, 2011

The Millett Jonokuchi Headphone & Speaker Amplifier

Our industrious friend Pete Millett has released another build of note, the Jonokuchi headphone / speaker amp. The Jonokuchi, like the Engineers Amplifier, makes use of a compliment of very reasonably priced Edcor transformers. Unfortunately, or fortunately depending on your tastes, the Edcor iron is only available with Royal Blue powdercoated bells, so if you'd prefer another color, be prepared to pay for your local shop to sandblast it off or purchase some unpainted bells of the same size.

The Jonokuchi, like the Engineers Amplifier, makes use of old television tubes that are cheap and readily available. It's a single-ended affair that uses 13EM7 tubes with 13V heaters. As stated on Pete's page: the amp design was optimized for headphone use, but still makes a fine amp to drive small speakers to reasonable levels. This is a relatively low cost build at approximately $200 in parts, just add a chassis. Assuming you make use of the PCB, you'll want to go with an 8" x 12" chassis as it should fit everything perfectly. Hammond makes a cheap one for ~$30, or you could get something more exotic like...

... a Hammond Chassis with Walnut Side Panels
...or a custom chassis from ebay seller po1019
Pete also put up plans for a Front Panel Express Chassis that comes with all the holes already trimmed out and labeled, but for nearly $300 for the chassis alone, I think I'll pass ;)

Jonokuchi with custom FPE panels
I was able to pick up my red board just recently from Pete and I've dropped a few parts on it so far.

The lovely red Jonokuchi board

Mostly populated, a few things left to source
I'll update in the coming weeks as the remaining parts arrive. Should be a fun little project. Now which film caps should I use... Obbligato, Mundorf, Sonicraft... oh the possibilities :)

UPDATE (3/05/11): I decided to go with the Hammond Chassis and AmpOhm Paper in Oil caps. Yes... the AmpOhm caps are a bit large, but with some creative mounting, they didn't pose a problem. Pete has the hole layouts in PDF on his website, so download and either print out yourself on a couple pieces of paper and line them up with tape or let Kinkos or Staples handle it on larger format paper. 

Chassis with drilling holes laid out on top
Drilling out the holes on the drill press.
I had Staples print the CAD drawings on the 11x17 paper, but despite saying not to resize in the instructions, they did anyway and I killed the first chassis, so be sure to measure the drawings first no matter what.

Mouting the AmpOhm PIO Caps

UPDATE (4/18/11): I finally finished up drilling the Hammond chassis, there were quite a few holes for tubes, transformers, a pilot light, the IEC inlet and the PCB mounting standoffs.

Front of the Chassis
Rear of the Chassis with oversized holes for Cardas RCAs

Bottom Plate

All holes were drilled with a trusty low-cost drill press and de-burred with a dremel tool. The rectangular opening in the back of the chassis was cut using a dremel metal cutting disc and then filed manually. Once complete, I gave the whole thing a once-over with 180 grit sandpaper.

UPDATE (7/8/11): Finally got the chassis back from my overly busy powder-coater. Now things are finally starting to come together. In place of the 5 watt 220 ohm resistor I placed a Hammond 157J filter choke (205 ohm) that was primed, painted and wrapped with leather. Cardas RCAs were installed on the back panel, along with some nice thick gold-plated binding posts that Parts Connexion was clearancing. I didn't want to splurge on Cardas posts as this amp will likely see a lot more duty as a headphone amp.

Board fitted in the powdercoated chassis

I designed a nice custom plate with the Japanese Kanji from Pete's Front Panel file and copperplate font spelling out "Jonokuchi". These little touches make the amp feel a little more polished and complete. The screws connected to the aluminum standoffs surrounding the tubes were depth-mounted as I'll be placing some decorative metal surrounds around them.

Custom plate embellishes the top of the chassis

UPDATE (8/2/11): The bell-ends are done being powdercoated in lovely a copper color and have been reassembled to the Edcor iron using my typical brass hardware and acorn nuts. I actually take the time to trim down each screw with a rotary tool to ensure that it's the proper length for the acorn. A few extra minutes of effort here and there goes a long way on the finished product.

The transformers were then mounted and the set of copper colored tube surrounds were screwed in place using very short screws as there is very little clearance between the chassis and the board. A jewel pilot light with a 12V LED was mounted on the left and connected to the tube heater pins on one side.

One the Jonokuchi was completely assembled and measurements checked for D.C., the amp was plugged in to verify the LEDs were lighting and the tube heaters were warming up. I then plugged in my trusty Panasonic tester headphones and had a listen. Unfortunately there was a bit of static noise depending on the position of the potentiometer. I ran a connection from the back screw of the Alps Blue Velvet pot to the chassis ground to ensure proper grounding, but that did not solve the issue. In Pete's design, the JP1 connection is used to connect AC ground to signal ground. After shorting JP1 with a short piece of buss wire, the noise was gone.

The amp itsself is on the lively side in my humble opinion, it possessed a detailed sound with taut bass and no rolling off of the high frequencies that I could detect. Unfortunately I was only able to source one pair of 13EM7 tubes (Raytheons), they tend to be a difficult tube type to find in the usual places. I feel that with the right compliment (some warmer tubes), I'll be pretty happy with the Jonokuchi.

UPDATE (8/8/11): I was able to get some custom engraved brass plates for the front of the unit detailing the operation of the push buttons, so those will be the final touch. Here's some final photos:

Jonokuchi Front
Jonokuchi Rear

Jonokuchi Side

Jonokuchi Inside

The Fine Print:
Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 


  1. Nicely done, looking forward to seeing how it turns out. I have been thinking about building one without the speaker outputs

  2. So..how does it sound?

  3. I'll let you know as soon as I'm done ;)

  4. I'm eagerly looking forward to your observations on Jonokuchi since I see you have built and used the Bottlehead S.E.eX. as well. It should be interesting comparison since Jonokuchi can be built for considerably less money compared to the S.E.ex.

  5. Indeed, both makers operate on different business models. Bottlehead sells full kits and their markup levels are different from Millett, which sells just the board and you are required to source the parts and chassis yourself. You spend more time in the latter case, but save a few bucks I'm sure. It might be nice to see Bottlehead offer "half-kits" similar to Hagtech.

    I do know the upgraded transformers on the S.E.X. are likely of higher quality than the high-value Edcors, so it may be difficult to make an apples to apples comparo.

  6. If you have not tried to put the circuit board into the chassis yet, don't solder the sockets in until you have put the board in. It won't work. Use sockets with out a shoulder and solder after the board is in.

  7. It's a very tight fit Al, but I can get the board in and out without issue. I may have made the socket inlet holes a little larger than necessary, but I have a pair of decorative tube surrounds that will fasten to the chassis and make everything nice and purdy ;)

  8. After some tube rolling, I'd say that the sound actually gives the Bottlehead S.E.X. some good competition. I'm using a pair of Sylvania coin-bases in each, and I'd say the highly modified SEX has a darker background and slightly more resolving upper-midrange, but other than that, the amps sound surprisingly close. The treble presentation is slightly different in both amps, but I wouldn't say one is better than the other.

  9. Very nice job, your workmanship is excellent and made every parts detailed arrangement !

    But the S.E.X use 6DN7 tubes, the Jonokuchi use 13EM7s, though I don't have any chance to hear the sound difference between 2 tubes... Do you think this might be the major reason the 2 amps sounded different ?

  10. Both the 6DN7 and 13EM7 are dissimilar doubles, just that one has 6V heaters and one has 13V heaters. I'd imagine one of the main differences would be the parafeed orientation and the higher quality xformers on the S.E.X.

  11. Iv'e decided to make the JONOKUCHI my first tube amplifier project -

    first stage is completed with about half of the board components soldered into place -

    (C11) Nichicon KX Series audio snap-in aluminum capacitor
    (C3,4,12,13) Nichicon VZ Series general purpose aluminum capacitor

    (C1,2) Vishay MKP-1837 metalized polypropylene film capacitors

    (all resistors except for R5,18,19) KOA / Kiwame carbon film 2W 5%

    (R18,19) Vishay/Dale Metal film 1/2W 1%

    decided to go with the Jensen 0.22uf/630V copper oil for the two coupling capacitors
    ....C5 & C6

    Might be a tight fit on the board though
    diameter: 25 mm
    length: 35 mm

    Have to wait and see when they come next week.....Ordered the rest of the board parts and two sets of tubes to try out when it's all finished

  12. Forgot to ask, Where did you find the decorative tube rings ? (copper colored tube surrounds )

  13. Those are from VT4C. They have many different sizes for different sockets.

  14. Hi, looks like I may be resurrecting and old post, but I had a quick question re: you build.

    I too had a slight buzz in the amp through the middle portion of the potentiometer and shorted JP1 as you suggested. Buzz was gone! Next step was to get rid of the slight hum by following the mod on Pete Millett's site (not sure if you had to do this or not). This successfully removed the hum, but now the buzz is back!

    As this is my first build, I'm still in the learning phase and was wondering if you might have any suggestions. Thanks for all your tips, I used a lot of them!



  15. Hi Chris,

    I did see the mod on Pete's site but have not implemented it yet. You can try to space the output transformers further from the power transformer, and you could try using a power conditioner if it's your power that's dirty. I've had good luck with PSAudio's Duet.