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

  1. pmillett Contributor

    The problem is that parts like the MP7770 have an exposed pad on the back side that is used as the heat sink. It has to be soldered down to a ground plane, and soldered well, or the part will overheat. So normally that requires reflow, either with an oven or rework tool (a fancy heat gun).

    It is possible to put a big through hole pad there and fill it with solder from the back of the PCB... it's a little kludgey, but I have done it that way.

    The pin pitch is also pretty fine for somebody without a lot of SMD soldering experience.

    Pete
     
  2. Heffa
    Aaah, then it's a little bit different - I didn't think of that :)
     
  3. ericj
     
    Well, I'm not personally very invested in this. I'm not dying to build something with the nutube just yet. 
     
    50W would be much nicer than 30W, particularly considering the typical power vs. distortion curves on class-D devices. If they say 30w, they mean 12w clean.
     
    I agree that the thermal pad is a consideration. And even though i have a cheap chinese hot air system and a bit of smd experience, I'm a bit wary of such devices at home. 
     
  4. HiGHFLYiN9
    I have to get an order into PCX and figured I'd add the parts I need for the NuHybrid :D. For those of us who prefer carbon film resistors, can the 475K be replaced with 470K 2%, and can the 33.2K be replaced with 33K 2%? T.I.A. 
     
  5. HiGHFLYiN9
    ...guess I'll have to wait for Pete to come back :wink:
     
  6. Heffa
    My NuHybrid is shaping up.
    I had to use a few oversized capacitors since those in the BOM was out of stock at Mouser, but there where enough space on the PCB so no issues at all there.
    I will not be using the original case, but a Hammond 15something case I had in my bin. That will also gives me enough space for an ALPS Blue Velvet and some nice Neutrik inputs & 6.35mm headphone jack.

    20170410_213358.jpg
     
  7. HiGHFLYiN9
    Looks great! I have the same helping hands / Panavise combo :D 
     
  8. Heffa
    Yea, the Panavise/HobbyCreek Helping Hand combo is awesome [​IMG]
     
  9. ericj
     
    Wow, that's over $100 in jigs to hold your stuff. 
     
    I just use this: https://goo.gl/C2dYoY
     
  10. HiGHFLYiN9
    The Quadhands from Amazon are really nice too, they are $40 or so.
     
     [​IMG] 
     
  11. Heffa
    What I like most about the Panavise jig is that it's so sturdy I can rest my hand on it when soldering, without moving the board in any way.
    The Hobby Creek helping hands I got separately later, because it integrates so well with the Panavise stuff.
     
    Anyway, we are derailing the thread a bit here [​IMG]
     
    When I added temorary power/input/output to be able to test the amp yesterday evening I was really tired, so just when I was about to test it I realized I had hooked the ALPS pot to the headphone outlet by mistake.
     
    Lesson learned - don't try to solder expensive stuff while beeing dead tired!
     
  12. gikigill
    Already own the SSMH and looking forward to the Nutube shortly if I can get the sale through:blush:
     
  13. tomb
     
    I've been using this piece of white pine for the last 10 years.  Seems to work well enough.[​IMG]  It's been through dozens of Millett MAXes/MiniMAXes, Starving Students, T1s, T3s, and any number of prototypes - also the NuHybrid.  Put the part in the PCB, turn it over and press down onto the wood while soldering to keep things flush.
     
    01-sm.jpg
     
    Yes, I use some helping hands when doing SMD, but even then - these were $3 (on sale) Harbor Freight specials:
    db02-sm.jpg
     
    A little electrical tape on the corners keeps the cheap alligator clips from scratching the PCB.  The magnifying glass provides a good steady back-support, too.
     
    I'm not sure what the piece of white pine cost me, but I will unfortunately have to bite the bullet and replace it soon.  It's getting some burn marks and too many indentations from pressing resistors flush against a PCB while soldering.
     
    [​IMG] 
     
    P.S. Oh - that's an old PC mouse pad underneath to keep the board from sliding. [​IMG]
     
  14. pmillett Contributor
    Sorry for the delay, for some reason I didn't get an email notification...
     
    Yes, 470k and 33k 2% are fine here.
     
    Pete
     
  15. Heffa
    20170417_124002.jpg
    It's alive! ☺️
    Time to cut out the front & back panels for the Hammond box I'm going to put the amp in...oh, and also test it with my good headphones. I have only tested it with some crappy no-name so far.
     

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