Pete Millett NuHybrid Headphone Amp

[Torq]

I have not tried it with a Noise Nuke yet.

I tend to run things like this off my lab-supplies if I think it’ll help (or at least to see if it does). Though it sounds just fine via the specified SMPS so far. I haven’t gotten around to doing any proper measurements yet, nor any audition-type listening, so hard to say if there are less audible/lower-level issues there.

I like the tone and the character of the little thing enough that I am planning an “all-out” build of it. Not because I think that will be in anyway cost-effective (it won’t), or that it will necessarily noticeably improve the performance, but purely because I think it’ll be fun to do.

But I am planning for a dedicated, internal, low-noise LPS with proper filtering, capacity and regulation, digitally-controlled 128-step analog volume control, front-panel adjustable digitally-controlled bias offset (with defeatable LED metering).

Ideally I’d like to use the digital bias control as a per-channel offset to a “master” bias setting, so you can dial in each channel to account for tolerance variations, and then use a single control to ramp the final bias voltage up or down, while listening, for both channels at once.

And then when I have all of that done, which will be using standoffs/additional boards connecting to the current stock PCB via wire, if the results are fun enough I’ll draw up a new PCB to accommodate the appropriate extra elements (e.g. the digital/analog attenuators etc.) and shock/vibration isolate the NuTube, likely on a separate, shielded, carrier.

Displays/meters and controls would be on another board, isolated from the main one.

Then a shielded metal enclosure, with appropriate cut-outs, and a view-port on top on which I plan to put a nice prism, so you can see the NuTube while keeping it safely shielded on all sides except the top.

Absolutely massive overkill.

And more about fun/variety/experimentation than necessarily improving the sound.

Chassis-excepted and LPS-excepted, it’s probably another $100 to $150 in parts. And between parts selection, circuit design, and actually putting it together, testing, and tweaking probably 100-150 hours or so of work give or take the time to layout a new PCB and panels.

[TylersEclectic]

That is really cool! I look forward to your build of this…I’m going to put together the baseline (with suggested upgrades) as soon as it comes in the mail this week (snow might cause a delay)

I’m excited to see what you come up with! and if it is possible to recreate it in a separate build, to my OG build.

[pukkita]

It does already have a 2H choke on the PCB… PSU input has an LC filter.

Used to the iron chunks used with regular tubes, looks like a liliput one

[pukkita]

Just found this those thinking on “displaying” the NuTube in a project (window on the box,. etc):

Carrier PCB with Korg Nutube 6P1 - low-power triode vacuum tube | eBay

Standalone “carrier PCB” is $6.

[Torq]

I’ve chosen my digitally-controlled analog attenuators and trimmers.

I’ve gotten the meters designed for measuring and displaying the absolute bias values for each channel on a 3-digit, 0.1v precise, 7-segment LED display (one per channel).

Now working on tying those in to a single control to alter the relative bias so both channels can be adjusted from a single control (once balanced individually).

Sadly some of this is going to wind up being SMT, as not everything I want to use is available as through-hole.

[pukkita]

I’m “salivating” will you create a new PCB?

I love bias indicators, though I was always worried of injecting unwanted bias while measuring it.

Is it going to be single ended?

One of the things I love about the Loxjie P20 is the volume control / input selector, an universal board based around NJW1195A would be killer for the DIY scene, IMHO much superior to pots and possibly cheaper.

[Torq]

My first pass will be using the existing amp in its current form, so it’ll remain single-ended.

The bias indicators, and the meters that drive them, will be defeatable in two steps. The first step will disconnect the meter connections, and disable the adjustment input, but leave the displays showing the current value (in volts). The second step will turn off the displays as well.

As I was thinking about that more last night, I thought it’d be cool to actually use vacuum fluorescent displays for the meters, so they’d match (roughly) the color and appearance of the glow from the NuTube (and because they have some nice old-school charm). Unfortunately the available displays, without salvaging used parts, are either a) about $100 a shot and/or b) require a microprocessor to drive. So that will have to wait for a subsequent build.

As for a new PCB, originally I was thinking that if the end result was good, and there was enough interest, I’d lay out a whole new board. However, now I’m thinking I can do all of this on a smaller 2nd PCB that’ll just sit on headers above the existing board. That can bring the necessary connection points up off the main board, including the tube (which can then be shock-mounted). Which would make it a potential retro-fit for existing builds (though you might need a hot-air/reflow station to safely pull the tube or pot off).

Doing an additional PCB (rather than just relaying out and expanding the current one) would also help if I do want to go in a direction that needs a microprocessor to run it, as it’ll make it easier to shield and isolate, power, and allow for more flexibility in parts placement.

Right now the meters and bias adjust design I am looking at do not need complex control logic. In fact, since each attenuator is a discrete piece (one chip per channel), they simply require power, and then to close the contact on either their individual up, down and mute pins, to drive the internal “wiper”.

And they’re a simple, comparatively large-pitch, SMD with just 8 pins each. 2 for power. 3 for the wiper (pot). And 3 for the control pins.

The prototype/test-bed I’ll likely just run wires to for the extraneous/broken-out connections.

[ProfFalkin]

@Torq - This, or the BH Crack? Which do you like better?

[Torq]

As long as you’re using higher impedance headphones (150 ohms or greater), then the Bottlehead Crack would be my choice - from a “how it sounds” perspective at least.

This (the “NuHybrid”) is obviously smaller, easier to build, cheaper and doesn’t shift in tone/control with lower impedance cans. It’s signature is also more immediately and obviously euphonic, at least with bias around 11v.

I like both of them, for different reasons.

[Torq]

While I was away, some new parts came in for my bias controls (digitally controlled analog attenuators) and bias meters (7-segment, 3-digit LED).

I had also decided to add proper, analog, front-lit, VU meters (more vintage/submarine-hardware in style) and those have arrived too. They’ll need buffers to avoid contaminating the audio signal and a way to calibrate them, but that’s easy enough.

I was going to do push-button up/down control on the bias control, but now I’m thinking about doing a “Steampunk” style build, and using plumbing hardware in an oversize case, with taps on rotary encoders for the bias settings … which will be a major departure from the simple, black, low-profile casework I had planned before.

Either way, I’ll post the state of the electronics build once it is working before I get to casing etc.

[TylersEclectic]

I still need to put mine together…and the Speedball… I am a failure of time management… I blame my lil dictator! And my ADHD (hopefully that is getting helped soon lol).

[PastorOfMuppets]

I prefer a tube voltage ohm meter to those solid state op amp models

[PastorOfMuppets]

So I thought I got the wrong pot and had screwed it all up but after replacing turns out the suppression choke was bad. So I’ve bypassed it. I’m wondering what problems that causes. Right now the sound is mono (edit: right channel works left does not), I’ll figure it out soon. But it works…mostly.

[PastorOfMuppets]

30 second review:

I was intrigued by this because I am a member of the high value and on sale club. I can make my own amp that would cost more if someone else made it? I’m saving money!!! Plus it would be a fun project and keep me busy for a while since I’m forever at home these days.

I haven’t soldered anything in 15-20 years and it was fun to do this. Honestly, I thought it was a nice project but a nice toy at first. This is not a THX unit, it’s got background noise and then there is that ping anytime you touch much of anything about the amp. I hope Amir can measure the SINAD of the ping when you move the amp (omg i wrote this sentence before googling other impressions and he has). But anyhoo, the amp sounded fine at first listen. Noisy so definitely not professional grade but it comes with a lot of satisfaction in building it so that all cancelled out.

Then I plugged it into a Burr Brown DAC I use with my Elegias. Oh hellz. Big improvement. I keep wondering far ahead what I am going to want for my work rig if I ever see people again and have to go back to cubicle land. It’s gonna be whatever works best with the Elegia probably, wanting a closed back solution, and right now this is making the cut. (I keep forgetting I can use IEMs though)

I have a Vali and a Lyr, and I’m loving the neutrality (and many other things) of the Ananda, but this is what you guys mean by having color and wanting warmth and stuff isn’t it.

[generic]

Question for @pukkita, @Torq, and @PastorOfMuppets, as my soldering iron is “burning a hole in my pocket” for lack of use after finishing my Crack.

Are NuTube amps worth it today, in 2021? I found a lot of info from 2016-2017 and even the one-time $2K Sangaku amp. It has now become a partial DIY kit for $170 on Ebay.

There’s also a circa January 2020 mobile NuTube amp kit in an Altoids tin format. One review spent as much or more effort on discussing measurements from the-site-that-shall-not-be-named as on its audio character.

The NuTube seems to have been initially designed for guitar amps and distortion pedals, and the reviews there are sometimes ho-hum. These products are said to sound good, but originally costly for what you got and not very different from other traditional guitar equipment. The NuTube guitar pedals are also much cheaper today than when released.

I’m asking only because I’m curious about the technology…as a project. These may be museum pieces in waiting, as you can roll and replace traditional tubes much more easily. Each NuTube runs $50, and there’s only model one that I know of.

[Torq]

I really enjoyed the ones I built, especially with the HD6XX and HD58X.

And when I say “enjoyed”, I mean both in terms of building the thing as well as listening with it. It’s a great, fun, little project, that yields an amplifier with a decent amount of power and a distinctly tube-like sound. I still plan to finish my “uber” build of the thing, in a balanced design (Pete has a balanced design published … since a year or more ago now …) with all the tweaky options I mentioned before.

I can’t think of much better to build if you’re hankering to put something together and have already done your BHC. This is a much easier build, overall.

Just bear in mind that you’ll need to run a smaller tip on your iron than you would for point-to-point stuff. I used a 0.6mm conical tip, and I wouldn’t want to use anything larger (except perhaps for the pot and the switch).

[PastorOfMuppets]

Torq says it better than I. the build is fun and easy. the amp has power and is very tubey. i maintain that an amp you build yourself sounds better because you built it. if you are really looking at apples to apples with $ being the thing, i don’t know if i’d look at the value of the tube. not sure what else is out there with the power and tube flavor of this thing at the price point of the full amp. only thing i have experience with is the vali 2+ and it’s very different, not nearly as lush.

[generic]

Thank you @Torq and @PastorOfMuppets. The Mouser bill of materials for the NuHybrid currently shows many out of stock and some discontinued parts. As such, I’m even more pessimistic about parts availability for the more complex Sangaku kit. The Nu:Tekt HA mobile kit is available. As shown below, it’s quite simple and may require only a 1-2 hour assembly. Do I even have a use case for a mobile, battery-powered amp when I rarely use the one I already have? Hmm…

[PastorOfMuppets]

ah yes the “search for replacement parts because things are out of stock” at mouser activity that takes longer than actually building the amp. i know it well.

[Torq]

The mint-tin version of the amp is not very good, in my opinion - though I think that’s mostly due to the power-supply.