[HiGHFLYiN9]

I've read several people comment that the Vcaps need really extensive burn-in, like 500 hours. Maybe you could run the jupiters and bypass w/v-caps.

 

[Whitigir]

I've read several people comment that the Vcaps need really extensive burn-in, like 500 hours. Maybe you could run the jupiters and bypass w/v-caps.

Dang!! Really ? That probably killed some tubes before it is done burning in lol

 

[tomb]

I mean, maybe? This isn't really balanced. The balanced and SE input signal both go through a THAT buffer to create a single-ended signal for the gain stage (the two sections of the tube are paralleled) and the balanced output signal is generated by a second output buffer with reversed polarity. That will give you a more voltage swing, but not much else.

Good call. There is definitely only a single-ended input and output from the NuTubes. Although, the NuTubes are dual-triodes, so the design to fully differential could've been done, perhaps.

Just an FYI, but there was a thread a while back from Steve Eddy that hotly debated the difference, re: balanced vs. differential. If anyone cares, the consensus from Eddy and some others at the time (Dsavitsk) was that balanced simply means the amplifier can operate in an overall balanced system, with compatible connections. Meaning, if the amplifier can take input from a balanced source and can provide output to a balanced source, then the amplifier is balanced. My guess is that in the Pro Audio world, the primary concern is for the losses/distortion through all the lengthy cable runs. Balanced cuts that out, or at least minimizes it significantly.

Anyway, that may be why Pete referred to it as balanced. I seriously doubt he was ever trying to mislead (not that anyone said that).

In the headphone world, many of us are actually interested in fully differential. That is where the equipment in question utilizes a signal that's truly split into its differential parts, throughout the equipment component, from input to output. It's this differential "expansion" that provides a doubling of voltage swing and slew rate on the output, which is what has an advantage with some headphones.

Ever since, Dsavitsk and I (and others) have attempted to distinguish between the two, settling on the term differential to describe a circuit that is not single-ended, regardless of its input/output connections. Of course, a differential amplifier with balanced input/output would be described as a fully differential amplifier. I don't know if that distinction means much to some people, but balanced tends to get thrown around a lot when the component may not be really fully differential.

P.S. Just an FYI, but there is a great benefit to the reverse design - using a differential amplifier circuit with single-ended input/output. It reduces or eliminates common mode distortion. It's the heart of the DSHA and T3/T4 designs by Dsavitsk of ECP Audio. As Beefy noted, truly differential connections are not as much of an advantage with a tube amp. The slew rate is limited by the tubes, but they have plenty of voltage swing already. Using them in a differential circuit (long tail pair, for instance) can yield great benefit because of the common mode distortion cancellation inherent in a differential circuit.

 

[Whitigir]

Agreed, the voltage swings are where the beef and the juices are at. Usually it is that Portable markets are utilizing Balanced output is to cheat a little and increase the power being delivered. For a desktop proper amplifier, SET is the blood and gut of it, recommended

 

[HiGHFLYiN9]

Excellent post Tom. It could certainly help matters for the industry to use the term fully differential to differentiate between balanced, pseudo-balanced, etc. Personally I'm glad for a new project and the extra power from a balanced connection so Pete's offering is very welcome, but I understand that some people are looking for a fully differential project.

 

[Beefy]

Just an FYI, but there was a thread a while back from Steve Eddy that hotly debated the difference, re: balanced vs. differential.....

Great post. Also worth noting, that fully differential amplifiers can be configured to accept single-ended inputs, and have single-ended outputs. So we do really need to all distinguish between connectivity (balanced vs unbalanced) and amp topology (single ended, push-pull, bridged, differential). I think it's an uphill battle to get it completely right and accurate, it's too easy to be lazy!

I do note that Pete did actually publish a 'proper' balanced amp based around the NuTube here: http://www.pmillett.com/Nutube_bal.html

But man, I'm finding it hard to get excited about this amp when looking at those distortion plots. The more I look at the NuTube in general, the more I struggle to see what problem it actually solves.

 

[Whitigir]

Isn’t the Nutube meant to be compact and reliable ?

 

[Beefy]

Isn’t the Nutube meant to be compact and reliable ?

Sure. But so is an OPAMP.

I guess I'm just really having a hard time seeing how the compromises for the NuTube make it a compelling solution versus classic tube designs, or solid state.

 

[Whitigir]

Sure. But so is an OPAMP.

I guess I'm just really having a hard time seeing how the compromises for the NuTube make it a compelling solution versus classic tube designs, or solid state.

I see your point! And you are right there. Other makers have been trying to implement Nutubes into their portable players as a compact resolutions for tube distortions on the go, like the AK SP2000T. I guess that is really where it comes into play, but still, for other purposes, I agree that classic tubes are a much better choices with tubes rolling as many possibilities and … pocket damaging lol!!

 

[Beefy]

I see your point! And you are right there. Other makers have been trying to implement Nutubes into their portable players as a compact resolutions for tube distortions on the go, like the AK SP2000T. I guess that is really where it comes into play, but still, for other purposes, I agree that classic tubes are a much better choices with tubes rolling as many possibilities and … pocket damaging lol!!

There's also the fact that the NuTube is reported to be insanely microphonic. Portable use is surely crazy.

 

[Whitigir]

There's also the fact that the NuTube is reported to be insanely microphonic. Portable use is surely crazy.

Absolutely agreed on that front. But that makes many people excited still. The key words is not what is being right, but what is being sold

 

[HiGHFLYiN9]

There's also the fact that the NuTube is reported to be insanely microphonic. Portable use is surely crazy.

It seems to be the luck of the draw. Some are microphonic, some are not. I built the Nu:Tekt HA-Kit and it didn't suffer from any microphonics despite me moving about.

http://www.nutube.us/HA-kit.html ...being able to adjust the feedback was a nice treat as well. If you google DIYAudioBlog and HA-K1 you can read more about it.

The other one I used with the NuHybrid I built would ring when the switches were adjusted up front, but was otherwise fine.

As far as benefits, it provides a tube signature and consumes very little power, doesn't generate heat, and has a long life. Implemented in the right portable DAP chassis I think it makes a lot of sense.

 

[Gizmo1k]

I finished my build last night unfortunately for me I had the polarity on d3 reversed and ended up letting the magic smoke out of the tlc555cp chip. Waiting on some spares and then I can give it another go. Big thanks to @jh4db536 and a few others on discord for helping me along the way.

 

[HiGHFLYiN9]

Sorry to hear about the difficulty, hope you can resolve it quickly.

 

[jh4db536]

Another revision, i think this might be the final datapoint for me. The CuTF are burned in now. They lost that metallic tinge and starting to sound more 'normal' so i thought it needed a retune.

I finally received my backordered parts to finish it. Ditched the last of the ceramic caps in the amp sections.

Very happy with the way this sounds now especially paired with my Philips dac and HD580.