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Post by CyberGene on May 9, 2017 12:22:55 GMT
I stumbled upon Pete Millett's website where he recently presented a very simple headphone amp that uses a very interesting modern tube made by Korg, the Nutube 6P1 Dual Triode. This is a low-voltage DHT tube that is employing vacuum fluorescent display technology. More about the tube: KORG Nutube. Pete Millet was part of the tube design so he is allowed to distribute the tube in small quantities to DIY-ers through his eBay store where he also provides the PCB for his NuHybrid Headphone Amp
Here's the schematic:    The PCB:  The final amp:  And now the most interesting part. FFT at 1kHz, typical tube type of THD with low order harmonics:  There are trim potentiometers that regulate the tube bias which also changes the THD profile so one can experiment and bring more tube "distortion" if he likes so. I've ordered the parts, the tube and the PCB, so in a few weeks should be able to give some feedback. Was wondering if anyone else has already built it? It will be my first DIY project and I hope I will manage to do it. Besides, it's a tube amp and a very safe one since it's low voltage (24v wall-wart adapter powered), so I hope should be perfect for a newcomer like me to the tube sound  |
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Rabbit
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Post by Rabbit on May 9, 2017 15:49:10 GMT
Looking at the board, I instantly thought ... Ember.
Not seen them before.
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solderdude
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measureutternutter
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Post by solderdude on May 9, 2017 19:08:40 GMT
These are indeed designed for guitar amps and such.
The amplitude as well as the amount of generated harmonics is MUCH higher than 'normal' tubes.
This means much more tuby-ness than normal tubeamps.
I can't predict what it will do for recorded music though.
For instance the 2nd harmonic is down 40dB = 1% where the Ember is -65dB (0.06%)
The 3rd harmonic (which is said to sound less 'nice' is an audible -60dB down (0.1%) in the Ember for instance it is an already inaudible level of -95dB (0.002%)
The 4th harmonic and above is below -110dB where in the nutube it is -65dB (0.06%)
No idea how it measures at lower output levels but that should be better.
So perhaps it sounds quite 'tubey' at lower output levels already but might sound 'dirtier' at higher output levels.
But it looks like a fun project for sure.
Do let us know what you find it sounds like.
It uses the exact same output stage as the Ember/Polaris/Solstice but at a much lower power supply voltage (the same as Solstice) and with 4x lower value output caps.
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Post by tupisac on May 9, 2017 20:18:48 GMT
This rectangle tube thingy looks incredibly sexy and modern. Love it. Pure 21st century. I want one just to hold it and feel the awe to modern science.
What always kept me from old tubes is the amount of fuss and stress. This looks like a starting point of a new revolution in audio equipment.
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solderdude
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Post by solderdude on May 9, 2017 21:05:46 GMT
That 'tube' exterior technology is actually quite old already and comes from the VU meter displays and early (Alfa) numerical displays of the good old cassette tape era. Basically a flat version of nixie tubes but using different Phospores to create a few different colours. Blue-ish, green, orange, yellow and red were possible. Like the ones below found in most cassette decks of those days as well as in tunersm, (alarm)clocks, (microwave) ovens, matrix displays.    It is basically the exaxt same old technology except it has 2 grids and the cathodes light up nice and green and is used primarily as a tube and not as a display. As said, it is basically only interesting for guitar amps and such and less suited for hifi. Still a lot of people will like what is does. |
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Post by tupisac on May 9, 2017 21:31:33 GMT
Sure, but one can argue what the true innovation is. It might be just an old idea redesigned, but the purpose and execution are brilliant.
I wonder if the physics and technology of the product allows for tweaking of harmonics levels which you've mentioned. If yes, then this could be one of the first products in line-up. Tube this small, with 30k hours of lifespan and needing fraction of power? Yes please.
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Post by CyberGene on May 9, 2017 22:42:16 GMT
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Post by CyberGene on May 18, 2017 9:51:40 GMT
The tube and the PCB finally came yesterday and I couldn't help but start soldering after midnight I haven't done anything DIY since I was in sixth grade (24 years ago), so I was kind of nervous...  I was ready with the soldering after two hours:  Tube glowing in the dark:  The NuHybrid put next to my solid-state discrete headphone amp:   First impressions are fantastic. Very smooth and and soft sound, can't really hear any big difference compared to the professional solid-state amp but I need to listen more since I was really tired. The tube is microphonic and generates noises if I knock slightly on the case but this subsides in a matter of seconds. I followed Pete's advice to set the bias voltage for lowest THD, however I may play later with the bias to see if I can make it sound more tubey Ultimately, this was a huge fun as my first DIY project and I am extremely happy with the results! |
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solderdude
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Post by solderdude on May 18, 2017 9:58:41 GMT
Looks neat and tidy.
All it needs is a nice enclosure.
A bit of a shame to be hiding that tube.
Perhaps a G1217 type of 'enclosure'? Plexiglass top and bottom plate ?
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Post by CyberGene on May 18, 2017 10:12:12 GMT
You've read my mind! I've seen the G1217 Polaris plexiglass case in the other thread and can't get it out of my head since! So sexy! Will definitely try to do something similar for the NuHybrid too.
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Rabbit
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Post by Rabbit on May 18, 2017 10:21:45 GMT
Well done CyberGene. Looks good. Tasks like that are difficult for me with all the little bit since I damaged my hand quite badly a long time ago so that feeling is a bit strange. Like permanently wearing a glove, so whenever I try to do anything fiddly, I have to have my torch close by to find bits dropped on the floor!!!
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Post by CyberGene on May 18, 2017 12:03:11 GMT
Rabbit, I am sorry to hear that  But I think you can always find someone to help you. Honestly, I would've done better job if someone was helping me. One needs to press elements from below, another hand to hold the iron and a third one to provide the solder... Mission impossible! |
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Rabbit
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Post by Rabbit on May 18, 2017 12:17:57 GMT
It's so fiddly for me that I don't even try any more. I took one of my fingerprints off with a soldering iron and felt nothing. Only noticed when I smelt cooking!!!
So now I don't even start things like that. Makes me feel a bit helpless but seeing the skin come away from a finger stopped me last time!!
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Post by CyberGene on May 18, 2017 12:39:33 GMT
Wow, that's scary!
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Rabbit
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Post by Rabbit on May 18, 2017 15:21:10 GMT
Is the vol pot touchy with the new amp? For me, with my Ember, I fitted a bigger control knob so that there was a slightly finer control. I found that it was getting powerful too quickly for me and didn't have an attenuator. Now though, I do so it's not such an issue.
Also, is tube noise low other than those microphonics when you tap? I found my tube on the Ember to be very microphonic and it turned out to be a tired tube. Just replaced it with another and it was gone.
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But I think you can always find someone to help you. Honestly, I would've done better job if someone was helping me. One needs to press elements from below, another hand to hold the iron and a third one to provide the solder... Mission impossible!