"Millett Hybrid" redux: NuHybrid headphone amp, using the Korg Nutube
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hav2uo4

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Got the upgraded pot and the EARs. Now I'm ready to go!
Awesome! When you're slinging it together I'd recommend soldering a wire into one of your ground connections you can use to ground the body of your pot.
 
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trevmex

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Awesome! When you're slinging it together I'd recommend soldering a wire into one of your ground connections you can use to ground the body of your pot.
Can you share a picture of how you did this? I read your description, but can't quite picture it in my head.
 
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hav2uo4

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Hope this works...Pete's multi-pot footprint is excellent for hacking a ground connection. I had to file a small notch into the inside of the case to clear the wire.
 
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Millett NuHybrid hybrid tube headphone amp complete.jpg

I added a cool little engraved plate to mine, feels complete now. I also built AMB's o11 power supply for it as a nice little improvement over the wall wart.

AMB o11 Power Supply.jpg
 
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SlingBlade

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I'm about to order the Buffer. Have any of you have played with bias of the NuTube to get more even order distortion, and if so, what are your impressions?
 
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trevmex

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As promised, here are the progress pics!
Photo Jul 20, 11 54 55 PM.jpg Photo Jul 21, 12 20 36 AM.jpg Photo Jul 21, 12 41 19 AM.jpg Photo Jul 21, 1 13 34 AM.jpg Photo Jul 21, 1 42 13 AM.jpg Photo Jul 21, 1 42 28 AM.jpg Photo Jul 21, 1 55 22 AM.jpg Photo Jul 21, 2 43 44 AM.jpg Photo Jul 21, 2 43 34 AM.jpg
And there you go. I don't have the right headphone connector to test it at home, so I'll let everyone know how it sounds tomorrow.

I highlighted hav2uo4's pot ground wire and the EARs. Hope they make it sing!
 

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trevmex

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I just tried the NuHybrid out with my Grado SR60i phones. Sounds great!!!

Now, I want to put a clear plastic lid on the setup with some slits for air to get in. Can anyone recommend a place to get a plastic lid for the box Pete suggested?
 
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Evgeni

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Guys, you were right about solving noise issues by grounding the pot: that solved my problem. However I haven't applied this fix permanently (like on the hav2uo4's picture above) yet, I just tested it with a wire. But in the meanwhile I replaced the switching supply with a linear supply I ordered from eBay and that kind of halved the noise.

However I am currently totally noise-free. Here's the "fix". I was mainly using my NuHybrid with my HD-650. However I recently bought Beyerdynamic DT-880 600-ohm and man, that's a combination made in heaven! The Beyers just sound incredible, it's a butter creamy sound. I can't hear them sound this way with any of my other amps. This amp really shines with these headphones. Really, guys, you MUST try this combination, it's probably my best setup ever! And they are absolutely noise free this way which I contribute to high-impedance (and low-sensitivity).

BTW, I tried to change the bias through the trims while listening to music and I can't hear any change whatsoever. It's either the harmonic content change can be noticed only with an oscilloscope and not audible or it's my ears (or I don't know what to listen for). But right now I just followed Pete's advice to set them at 11V.
 
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hav2uo4

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I just tried the NuHybrid out with my Grado SR60i phones. Sounds great!!!

Now, I want to put a clear plastic lid on the setup with some slits for air to get in. Can anyone recommend a place to get a plastic lid for the box Pete suggested?
Build looks awesome, nice job. Glad it's working out for you. Not sure about a plastic lid. Data sheet seems to suggest that isolation from the air (no slits) can be better for microphonics (I smacked a fruit fly ~10ft away and it started ringing...haha). But the regulator does get toasty, it probably needs some airflow (I squeezed a heatsink on mine which is somewhat visible on the previous picture I posted).
 
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hav2uo4

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Guys, you were right about solving noise issues by grounding the pot: that solved my problem. However I haven't applied this fix permanently (like on the hav2uo4's picture above) yet, I just tested it with a wire. But in the meanwhile I replaced the switching supply with a linear supply I ordered from eBay and that kind of halved the noise.

However I am currently totally noise-free. Here's the "fix". I was mainly using my NuHybrid with my HD-650. However I recently bought Beyerdynamic DT-880 600-ohm and man, that's a combination made in heaven! The Beyers just sound incredible, it's a butter creamy sound. I can't hear them sound this way with any of my other amps. This amp really shines with these headphones. Really, guys, you MUST try this combination, it's probably my best setup ever! And they are absolutely noise free this way which I contribute to high-impedance (and low-sensitivity).

BTW, I tried to change the bias through the trims while listening to music and I can't hear any change whatsoever. It's either the harmonic content change can be noticed only with an oscilloscope and not audible or it's my ears (or I don't know what to listen for). But right now I just followed Pete's advice to set them at 11V.
Interesting PS observations, Evgeni. I got some promising results with another method. I was trouble-shooting some noisy Russian tubes on my project amber amp and found that my noise problems went away when I ran a ground wire from my mains line to the negative out from the switching regulator (be super careful if trying this). Dead silent. Tried it on my nuhybrid with the same results. Crazy quiet! Now my work computer sound card seems to have an unreasonable noise floor! YMMV, but I seem to have some really dirty AC.
 
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