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Design of a Korg Nutube Amplifier Part 2: Prototype

Karl is a design engineer with over a decade of experience in high speed digital design and technical project leadership in the commercial electronics sector.


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November 20, 2017 15:22

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I have read with great interest this article using this new type of valve. Apart from low power requirement, low operating voltages and compact size, I don't think it has a lot going for it. The gain is very low by any standards and the output voltage swing is only a volt or so. As a part-time muso, builder and repairer on many guitar amps over a period of more than 30 years, you can make a simple all conventional valve based amp with around 15 watts of power and a great sound
using those antiquated things we call valves. Part of the sound of a serious musician-friendly amp is choosing the right operating points for the valves and the frequency response of the tone controls.

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November 20, 2017 15:23

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Forgive a naive question. I need an amplifier and#wa wondering if this could be used as a "normal" amplifier leaving out any guitar-specific. I am obviously not well versed in Analogue electronics. I do like the idea of a valve amplifier though.

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November 21, 2017 15:33

@B-DOG It should be ok, you may need to put a " impedance buffer" up front depending on your source impedance. The design in this series is not going to be overly guitar specific but we are designing a mono amplifier.

November 13, 2017 11:52

I have been building overdrive/distortion mechanisms since I starting playing with electronics (and electric guitars). This includes amplifying with different types and amounts of non-linearity using transistors, operational amplifiers (OA) with diodes, leds and mixed, and also more recently using digital signal processing.
It is always difficult to summarize something about this theme but my general understanding is that tubes sound well because they do not amplify linearly.
There is almost always some degree of distortion, subtle at low levels and getting more and more noticeable IN A GRADUAL MANNER, as you increase the drive.
So, one interesting thing to do with this tube is to drive it into non-linear zones perhaps with an OA, from light to high overdrive.
The biasing can play an interesting role in making the output more or less asymmetric.
The rest is filtering: before the nonlinear element, to get an approximately even level throughout the notes range a guitar; and after, to control the amount of high frequency in the spectrum generated by distortion. But there would be so much to say about the filtering alone...

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January 22, 2018 09:48

@amonteiro I think that tube distortion is pleasing to the ears because they have predominantly even harmonics, which musically correspond to the same note, one o more octaves higher, while odd harmonics are out of tune. The soft and asymmetric clipping contribute to this type of distortion more pleasant to the ears.

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