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

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  1. silverfishla
    Stupid question. Are the opamps in this unit singles or duals?
  2. trevmex
    Got a part number for your heatsink?
  3. trevmex
    Can you send a link to the linear supply you bought?
  4. trevmex
  5. hav2uo4
    577002B00000G. Any std package with 0.25" fin height or less should work. Might be able to pull off up to ~0.40" if mounted backward (pointed away from the 1/4 jack). I have a few in that range in my cart for whenever I pull the trigger on another digikey order. Even with the small heatsink I measure up to ~140F. Probably OK, but I'd prefer to have it run cooler.
    trevmex likes this.
  6. trevmex
    Well, I accidentally left my NuHybrid on all day while I was at work and came home to listen to some music tonight. It sounds amazing having been on all day. I imagine that isn't the best idea, but the difference is noticeable!
  7. silverfishla
  8. hav2uo4
    Interesting module. Datasheet mentions unity gain stability issues and output current isn't as high as the OPA551, so wonder if you'd run into issues with harder to drive HPs and higher volumes. I haven't tried rolling myself as the OPA551s seem to be great performers, but keep us up to date if you try it.
    silverfishla likes this.
  9. hav2uo4
    Ha, I've done the same. Did sound good, but it may be because I'm coming back to a warm amp after a rough day at work. haha.
  10. Evgeni
  11. Sythrix
    I just built this and am really enjoying it but had a few questions about the upgraded pot. I installed it and also put the grounding wire on, but it whenever I turn the volume up or down there is distortion during the actual turning.

    Also, at the very bottom and top end the amp just starts crackling and hissing. If this is the behavior of a $40 pot I'd hate to see the original, but I think it is something else, maybe something I didn't do correctly? When not changing volume it sounds sublime. Anyone else have this behavior?
  12. pmillett Contributor
    For the input buffer transistors Q2 and Q3, did you use 2N3904 transistors? I saw some oscillation that produced noise like you described when I used FETs in those positions.

  13. Evgeni
    Yes, I have this behavior too with the upgraded pot. Slight hissing and cracking at the bottom and top positions. Other than that it’s a great little amp and it’s currently my main amp.

    Pete, I am using the 2N3904 transistors, so probably the reason for the top/bottom noise is something else?
  14. Sythrix
    Yes those are the ones I ordered per the BOM. I remember I put them on first for Q so I wouldn't confuse them.

    It sounds good to me and honestly I don't care about the extreme bottom and top because I'll never actually go there. Just want to make sure I didn't mess anything up.

    It could be they just sent me a slightly dirty/imperfect pot which causes the noise during turning? Or maybe I need to redo the ground connection?

    Well good to know I'm not alone.
  15. Sythrix
    Just got home and confirmed the 2N3904s are in Q2 and Q3. I think it must have something to do with the pot itself or some failing I haven't seen yet on my install or grounding of it.
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