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"Millett Hybrid" redux: NuHybrid headphone amp, using the Korg Nutube

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  1. SasaKudo
    Thx. I'm currently designing my case. It will take some days until I got the 3D print right (PETG). Hopefully the big MOSFET won't radiate too much heat for the case to handle material wise.
  2. Zemo Contributor
    I've missed all the diy tinkering, so I thought this might be a good project to get back into practice with a soldering iron. Thanks for putting this together, Pete!

    One question - I have a bunch of wima film caps at 250v 1uf...any benefit to using these over the 1nf caps anywhere? Just trying to think of easy upgrades with parts I've got lying around...
  3. pmillett Contributor
    They might be difficult to fit on the PCB, but the 1uF caps would work fine. You will get a bit better low frequency response...

  4. arteom
    Great looking build!
    silverfishla likes this.
  5. flyinggeek
    Just finished my NuTube and love the way it sounds. Also laser cut a case for it...
    01509207733015.jpg 01509207661171.jpg
    silverfishla likes this.
  6. GunnerXL
    Just received the board today, but the opamp is currently sold out in mouser. Can anyone would kind enough to suggest another op-amp to replace OPA551PA in this? i'm relatively new in audio, doesn't have too much experience with op-amps.
  7. SasaKudo
    Your forum profile says that you are located in germany. If that's really the case, you could order the OPA551PA from reichelt.de oder conrad.de since they both have the chip available for order. I also thought about replacing the OPA551 for something different, but in the end didn't do so. The OPA551 has a nice hight current output and is kinda nice to use as a buffer opamp.
    GunnerXL likes this.
  8. SasaKudo
    I finished my 3D printed case. You can find the files on thingiverse.

    IMG_20171111_170541.jpg IMG_20171111_170547.jpg
  9. randytsuch
    Nice case. How's the temperature inside? Not too hot?
  10. jekjek
    Nice case
    How much it cost?
  11. SasaKudo
    Only the linear regulator gets hot and there is still enough headroom for air to flow through convection. Since I used PETG (which is stable up to ~80°C) there shouldn't be any problem and my test leaving it on for 12 hours didn't show any real heat problems.

    Print takes around 14 hours on a Prusa i3 MK2S. I think I used around 150g PETG, which results in material cost of around 4~5 €. If you don't have a 3D printer, you could go to a Makespace or Fablab and print it there. That would cost you around 20~30 € here at my town.
    jekjek and randytsuch like this.
  12. silverfishla
    I received a pair of Burson V5i single op-amps a few weeks ago and I must say that these little silvery guys are incredibly great sounding in this amp.
    I've let the op-amps run in the Millett Nu-Tube amp for about a 100 hours total, just to let things settle in, as things tend to do...

    The op-amps that PM provide on the BOM list, are actually good sounding already. They sound clear and concise. I wanted to see if I could find a more tailored sound to my liking though.
    The Burson V5i Singles sound different from those on the BOM list. I think they sound much better. They have a certain enveloping characteristic that is very engaging and lush.
    I think that they add depth to the soundstage and have a very pleasing and clear vocal presence. I especially enjoy how these make a female voice sound bold and present, not tinny or thin. Just great here.
    The V5i also adds a nice pillow of bottom end that makes the Bass sound closer to what I like to hear...energetic, bouncy, and well rounded. It's just does a great job of enveloping you with sounds instead of presenting them in front of you. With the V5i, I think I have found my personal favorite so far in an op amp for this amp.

    Now, I also have the Sparkos Labs singles. I like those too, but I actually think, in this case, the Bursons beat those ones out. The Sparkos Labs singles are extremely up-front and bold. It's like everything is turned up to 11 on those (I even turned down the gain to about 10). Bass is up, Mids are up, Treble is up. Those are very clear sounding too, but are a bit fatiguing to listen to for long periods of time. The Bursons just have more space and lushness with it's clarity.

    I also used a Pono Player, Shanling M3s, Aune M1, and a Zishan Z2 as my sources. You know, source matters. I found that the Pono Player had a nice mix of analog quality and clarity through this amp. The M1 has a really bold LO, but very clear sounding. The Shanling was decent but not very warm. The Zishan Z2 just delivered a full analogy sound which is pretty impressive and headphone filling.

    Also, I used Sony Z7, Sennheiser 650, Beyerdynamic T90, Massdrop AKG KXXXXX as my headphones. The Sony's are the best match here for me with it's big soundstage and bolder bass. I also really liked the AKG set with this amp and the Bursons, a really spacious musical pairing.
    Last edited: Dec 8, 2017
  13. drpro
    Thank you Pete for such a nice project and easy build. Finally got all of the parts from Mouser and Digikey, took about 1.5 hours to construct. Applied power and works well and sounds great.
  14. drpro
    Finally got a pair of Burson V6 vivid opamps in place. Still letting them age. Sounding great though.
    silverfishla likes this.
  15. coinmaster
    I wouldn't touch the circuit design of this amp with a 10 foot pole (no offense to the designer) but I am curious to know how the nutube module compares to traditional tubes. Any thoughts?
    Last edited: Dec 30, 2017
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