Pete Millett NuHybrid Headphone Amp


#21

So … thanks to an unexpected internet-outage, a planned-but-dreaded 2+ hour conference call, and a general desire to cause trouble … the deed is done, at least for the stock-parts build …

It is a super-easy build. I was able to do it while on my conference call, and the entire assembly, including testing and biasing, took a shade less than 2 hours (it’s not a race; take your time). Still not sure I’d want to do it with a 1.6mm tip on my iron though … the 0.5mm I was using was as big as I’d personally want to go (except for the power/RCA/headphone sockets, switch and regulator).

My first actual listening test with it, I used the Grace SDAC and the HD58x Jubilee. And the results were sweet, rich, warm, and clearly imbued with some, quite lush and enjoyable, harmonic distortion products. It might be a good, basic, platform, to illustrate to someone what tubey-sounding-tube-designs sound like vs. pure, inexpensive, high NFB, solid-state designs sound like, as it has a definite and immediately obvious signature.

I had had the thing powered up for probably 20 minutes before first listening (see below on biasing it), and when I plugged the HD58X, even though they were not on my head/ears, the impact of the headphone socket seating home caused enough microphonic ringing that I could clearly hear it. And that took a good 10 seconds or so to fully abate.

That said, with the thing sitting on the desk, while I am typing, even with no music playing the staccato impacts of my mechanical keyboard are not inducing any further ringing or microphones. But if you ever want a demonstration of “tube” microphonics, the above would be a good place to start!

The tube itself looks, as one would expect, like the VFD displays (common in ovens, handheld video games from the 1980s, early calculators etc.) of old. It’s quite charming and I think any design that uses Korg’s NuTube should make it visible at some level.

Yes, I wish it glowed orange (or purple, but tubes, VFD-or-otherwise, don’t do that without LED-assistance), but that’s me.


Some thoughts for potential builders/users:

  1. Definitely do the TDK pot upgrade. Feeding the HD58X, using the SDAC as a source, about 10 o’clock on the pot is as far as I dare turn things up, and it is 9 o’clock before I am only just out of obvious channel imbalance.

  2. For the power LED (D5), the dot on the silkscreen appears to be in the wrong place. For the capacitors, which is what the assembly instructions direct you to follow here, the dot indicates the anode (+). However, the dot for D5 is on the side of the cathode. Tracing the circuit shows that the dotted (square) pad is indeed the cathode. However, if you install the LED in it’s naturally forward-facing orientation you get the proper operation - I’ll ping Pete and see if I’m either interpreting his instructions incorrectly or if they’re actually reversed.

  3. When you get to the point where you bias the two triodes, leave the unit powered up for about 10 minutes before you start. Otherwise you’ll be chasing the slowly drifting values as the circuit (and tube) reaches full thermal equilibrium.

  4. This definitely likes higher-impedance headphones (reasonable given it’s OI). It’s nice with the 58X (150 ohms), better with the 6XX (300 ohms) and leans towards bright with the HE4XX (35 ohms).


So, in short … a super-easy, entirely fun build, that results in a clearly euphonic, and quite pronounced tube-like presentation, for bugger-all money, a minimal investment of time and skill. A Liquid Spark, Magni 3, Atom or Vali 2 likely measure way better (at least in distortion), but none of them have the sweetness or lushness of this little bugger.


#22

My parts will be arriving over the next week or so…maybe even 2weeks as I believe Pete is out of office (vacation maybe?) lol…he emailed and said he would ship out after the 1st. I’m looking forward to putting this together though…always fun putting adult legos together =) along with real legos lol


#23

I’ll be taunting you with my 2nd build by then, then! :wink:

Given how enjoyable this basic build is, I have in mind something a bit more exotic for “V2”:

First, a proper, shielded/grounded, metal enclosure. Into which I plan to include an ultra-low-noise, filters and buffered, linear supply.

Second, a shielded/grounded sub-structure for the amp itself, as it is quite susceptible to external RFI/EFI/MFI (I can induce noise in the left or right channels based on where I situate the SDAC in relation to the tube).

Third, a suspended, damped, mount for the NuTube … it is impressively microphonic otherwise!

Fourth, doubling up on Pete’s design to produce a fully-balanced/differential implementation. Things are sensitive enough here that I think the CRR potential is worth exploring.

Finally, maxing out every possible component … even though I suspect any gains from which are likely to be hard to find with a $1M LeCroy, never mind my “free-with-a-shag” ears …


#24

Ha, “free-with-a-shag” ha…

I’m looking into custom enclosures also, but I’m sure I won’t implement as well as you will. I will probably find someones 3d printed deal, or something on Amazon that fits it. I would like to create a window/magnified window over the Tubes though…I agree with you on how good they look. Now I wait…

I look forward to seeing what you come up with for your second build.


#25

This is on my to-build list once I have the spare cash to mess about with it.

First up, though, is making a video showing a Garage1217 Project Sunrise III build. If that goes well, I’ll probably also record building this thing.


#26

A brief update …

The TKD pot did not, as it happens, fix the channel-balance issue completely. It’s better than with the default Alps component, but it’s not a complete fix (this can vary with individual pots, so yours may be different).

At this point I would add some additional static attenuation ahead of the pot rather than getting fancy with expensive boutique parts. And for the full-on 2nd build I may simply substitute a digitally-controlled analog attenuator to get perfect channel balance regardless of setting.


#27

Funny that a builder at another forum build it and used it as preamp on a meet with an Audio Note DAC and more fancy gear… and Audio Note got interested on it!


#28

http://en.cayin.cn/products_info?itemid=115

@Torq, @pukkita,

Looks like this high end DAP is using a similar tube in it very cool, I can’t wait to build this!


#29

Yep, the Cayin N8 has a NuTube based single-ended output option.

I’ve been toying with the idea of buying an N8, even talked to Musicteck about it. Only two things are holding me back at the moment. The first is that the A&K players have spoiled me with direct streaming access to TIDAL and Qobuz, and the second is that the N8 runs Hiby software.

If the former gets addressed I can probably overlook the latter.

But if I’m going to have to use my phone or tablet to get to the TIDAL and Qobuz content anyway, then I’d rather leave the extra device at home and just run IEMs out of dongle.


#30

I really enjoyed my experience buying from Musicteck (Cayin MKII) plus it was on sale…and as you know I have been biting at the bit for a random new piece of gear lol. I don’t use DAPs enough nor IEMs to justify the purchase of higher end gear in that realm, then what I already have.

I like the look of the N8 though it reminds me of Retro Future Star Trek gear lol.

I get not wanting the Hiby software I have the R3 (kickstarted) and even though it is fine it’s implementation of Tidal and no Spotify (Spotifys is the issue here) makes it less than Ideal…

I am really looking forward to Qobuz coming to the states though as I’m not the biggest fan of Tidal…I’ll probably go Audiovana+ when it does finally drop and really start building out my FLAC library…I might even bite the price of a lifetime Roon subscription, as I actually really like that UI, but at this time I wouldn’t take full advantage of it.


#31

Happy too see some attention on this! I had arranged to get a bare bones board from Pete right after thsi design went online, contingent on if I found a builder. Sadly I never found one but alas here it is!

@Torq I’d love to see the stock unit run a little tour among are lvl 3 members!


#32

I saw the discussion on r/headphoneporn about you little project. It fascinating that you can get tubes built into something as small as a Dap. I saw some pics of the said chip that you’re going to utilise and it looks really cool. I am looking forward to your exploits with this.:grin:


#33

For those in EU, the TKD pot can be sourced from HiFi Collective (UK):

I used a 50K pot instead of the 10K one, listening position at 12, haven’t noticed that much channel inbalance, though it may sound scratchy at the beggining at certain positions; just “work it a little” and scratching goes away.


#34

Building this is very easy.

I’d say it’s quite a lot easier than the Bottlehead Crack in fact - itself a very straightforward build.

You really don’t need much more than a reasonable temperature controlled iron with a fine tip ($30-$100), some 60/40 rosin-core solder (<$10), an anti-static mat/strap (<$20), and a pair of flush cutters ($5). And then a basic auto-ranging digital-multi-meter to test and bias the thing ($45 and up - and available cheaper still if you are comfortable manually setting its range and mode).

Now, I would, personally, recommend not going cheap on the iron or meter. A soldering station, be it Hakko or Weller, for about $100 will make your life much easier, as will going for at least the ~$45 Extech EX330 DMM.

It literally needs less tooling than a basic headphone cable or point-to-point amp. There’s not even any stripping, measuring or twisting of wires.

If you’ve never soldered a through-hole PCB like this before, then another $10-15 on a couple of “practice soldering kits” should be enough to get you there. Just don’t go for the SMT ones!


I could be persuaded to build these for people (here). Be warned that it almost certainly won’t be cost effective, though (it is no longer “DIY” if someone else builds it for you)!


As for doing a tour of it, that’s also probably not cost-effective. I think enough people here either have, or are already planning to build it, and post their impressions, that’ll it get proper coverage. And it so inexpensive that sending a unit around will cost more than it’s worth in very short order.

Those that want it, but can’t/won’t build it, would get to hear it … and then be stuck in regards to getting one anyway.


#35

I’m trying to figure out how I am going to build a wood enclosure for this. =/


#36

With the TKD pot the channel imbalance is gone sooner (at lower level), and is less pronounced, than with the stock Alps pot. So it’s better, for sure, but not a 100% fix.

Before doing the 2nd build, I figured the TKD pot would have to be a much bigger improvement in that regard than it was. Having since done it, I don’t think the change is worth 16x as much for that one component, or 35% of the total cost of the build. If it had eliminated all channel-imbalance, I would think differently about that.


#37

I was going to just go to a maker space (online even) and just having one 3D printed to my parameters…I want to see if I can get a magnified window over the tube!


#38

@torq have you built and tried a Noise Nuke with this? Maybe even just integrate the choke right into the build if it works.

I’m trying to figure out which parts I’ll upgrade before buying materials.


#39

I think this is what I’m waiting to hear about. Do the cap upgrades make a diff, volume pot, etc. Seems we have the answer on the pot…

Edit: I’m waiting for someone to put a GoldPoint attenuator in. LoL


#40

when one single upgrade costs more than the sum of the rest of a things parts lol…this hobby is so much fun…in part because of how ridiculous you can get with it if you want to