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

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  1. pmillett Contributor
    Well, I'm not real sure what would be causing this. I didn't notice noise like that on the one I built with the upgraded pot.

    The noise that was caused by oscillation using the FET was very loud. I would expect a little noise as the pot hits its limits, but nothing terrible.

    Sythrix likes this.
  2. Sythrix
    Not a big deal. I might tear it apart one day to see if I can figure it out, but for now it's just not enough of an issue for me to bother. The sound is so good that I am making it my main bedroom amp for music and TV/movies.

    Anyways, thanks for getting back to me! I am a fan of your work and am just about ready to start the Butte to accompany my PC.
  3. trevmex
    I have the upgraded pot as well and grounded it as well, it hisses at the very bottom and crackles at the very top. I don't get distortion when tuning, though (I used all the recommended upgraded parts on the BOM/site).

    The amp is hyper-sensitive to any jostling, though. I put EARs on it, which seems to help, and I bought the enclosed version of the box Pete recommends (but haven't gotten around to putting the top on yet).

    Still, I love it, though. I am thinking of making a DAC to complement it, but haven't decided what to build...
  4. Sythrix
    The distortion while turning and at the bottom and top seems to be fading away with time. I think I was shipped a substandard pot, but since I already soldered it, it's not eligible for return.

    I used "Isolate It!" Sorbothane feet to steady it, which seems to limit ringing to when I plug in a pair of headphones or very slight when I am adjusting the volume.

    I also am going to build a DAC!

    I decided on the https://www.amb.org/audio/gamma2/ (which requires that you also build the γ1, as it's an extension to it). It's basically two DACs and outputs in one case. That way I'll be able to wire two different amps (if I want) to the one brick housing the γ2 and γ1 (with one slightly higher quality output, given the more advanced γ2). Came out a little over $300 after all parts and a σ25 power supply with the σ78 regulator (optional, but lower noise than wall-warts). Could probably easily do it in the low to mid $200 range if you just used the USB power or something. There really aren't a lot of options for DIY DACs out there.

    I was going to go for the γ3 but the cost of all the parts and the front panels, on top of my non-existent knowledge of building power supplies, led me towards these builds instead. I'm going to have someone guide me through putting together the σ25 power supply so I at least get some familiarity with building them before attempting something as complicated as the γ3's.

    I'm just a little concerned about the reports I've been reading of the old SSMH and how it sometimes damaged the γ2 and γ1 because of some kind of power problem. I'm guessing it's not going to be an issue, but Pete did say the NuHybrid was based on the old Millett Hybrid design... All the parts are already on their way, so I hope it doesn't have the same problem or I'll be building another DAC soon enough after this one, lol.
    trevmex likes this.
  5. silverfishla
    I'm currently building this amp right now. In the wings, I've got some Sparkos Labs singles waiting to be installed in this when it is finished. I have installed some Nichicon Muses KZ capacitors for the big ones and fine gold (like in the BOM) for the small ones. I have a question though...which Capacitor placements on the board are the most resposible for the sound of the amp? Which ones are resposible for the input section and the output section? Sorry for such a dumb question, but I am basically building this like a "paint by numbers" and don't really know what capacitors on the board do what. Reason I ask is, I have been changing caps on a portable tube amp recently and found that I really like the sound of those Nichicon blue Audio caps that are available. I want to know which caps on the nutube amp (should I swap them out) are the most responsible for the "sound", so I can see if they make a difference (when I finish my build)
  6. Sythrix
    I'm sure someone more knowledgeable will jump in if I'm wrong, but looking at the circuit, C3 and C6 are directly before you reach your relay, then the phones themselves. However, don't discount the small electrolytic ones, because the Nutube is using them, per the NuHybrid website:

    The output of the buffer is coupled using a 10uF capacitor into the Nutube grids. http://www.pmillett.com/nuhybrid.html
    Which to me says that they are responsible for the sound being delivered to the op-amps, or the "buffer" stage. In other words, all of the electrolytic capacitors are probably important. That said, a good capacitor is doing its job when it doesn't affect your sound quality...read this here (go to post #8) by stv014 (I don't know how to properly link/quote from a separate thread, if there's a way to do that) who explains it quite well I think.

    I say use whatever capacitors make you happy or look the best as long as they are within spec, because if they're doing their job right, all that's going to matter is how well they lend an aesthetic flavor to your build. Good luck! Also, I would love to hear how those discrete op-amps work out for you.
    Last edited: Sep 24, 2017
    silverfishla likes this.
  7. pmillett Contributor
    Sythrix is correct, those are the most important.

    The input coupling caps C20 and C21 are also directly in the signal path, but they are smaller film capacitors and if you use what's on the BOM (Wima) they are already pretty good.

    The problem can be finding better electrolytic caps that will fit on the PCB. Audiophile electrolytics tend to be bigger than normal ones. The BOM has Nichicon "Fine Gold" caps, which are pretty good. You may be able to find Elma caps that can be made to fit as well.

    silverfishla likes this.
  8. silverfishla
    Thanks guys!
  9. silverfishla
    Hey guys. So I'm sort of in the last 1/3 stretch to finish my amp build. Waiting for some parts to show up or come to be in stock. I have a few very basic questions... 1) I've decided to lift some of the components off the board in order to fit in my casing better and have ordered some more panel mount friendly parts. My question is, what is the right size wire to wire the components (jacks and rca) to the board? Does it matter what wire I use? 2) Does anyone know of a good panel mount DC jack and headphone jack? They all seem to be of the same quality. Is there some that are nicer looking?
    Here are some pics of my project so far... Millet1.JPG Millett2.JPG
  10. HiGHFLYiN9
    Looks very nice. The wire length doesn't matter, you can mount the RCAs wherever they look aesthetically pleasing. If this were a larger build and you had to run the wire a foot or longer, then shielded wire can be of benefit. 24 gauge wire is generally best for signal, although if you have something between 20-26 laying around it will work fine. For the headphone jack, a lot of people like the Neutrik locking jack or the Neutrik NMJ series, at least in the headphone world. Switchcraft seems to be the go-to in the guitar market. Make sure to order a stereo version (if you shop in a hurry, the monos look very similar). The DC jacks are all quite similar. Switchcraft would be a good brand if you were looking for one.
    silverfishla likes this.
  11. CJG888
    +1 on the Neutrik locking jack.
    silverfishla likes this.
  12. silverfishla
    Thanks, I'm going to look into it. I do have some 20gauge wire that I can use. I probably will use it, since I have it. It's pretty nice SPC wire milspec.
    Guys, I saw the locking jack...and I like it...but it might mess up my aesthetic! Hahaha. Maybe if I can find a silver one....
  13. silverfishla
    Hey guys. Does anyone here have some extra parts? I can't seem to source what goes in K1 and D1. K1 is: NEC Tokin Kemet-PCB Low signal relay PCB 24v DC non latch. D1 is: ST Microelectronics- Transient Voltage Suppressor SM6T.
    These two items are on backorder from Mouser and one won't be in until Mid November and the other in January!
    Are there other parts that I can use from Mouser that will work? Sorry, I just can't reliably figure out what I'm looking at there. Brands, voltages, etc. I just don't want to get it wrong.
    If anyone has an extra one of these I'd be willing to trade for something that you might need. PM me.
    I have switches, caps, copper shielding tape, guitar pots, knobs, etc. Stuff you might be able to use for this or other electronics builds. millamp.jpg
    Last edited: Oct 7, 2017
  14. pmillett Contributor
    On the PDF and XLS BOM on the web page, there is an alternate part shown for the relay which looks to be in stock at Mousey. For D1, just search for 'P6KE33A'. Any manufacturer is fine, there are many.

  15. pmillett Contributor
    Gotta love autocorrect. Mousey = Mouser.
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