Mobile tube sound for headphones and almost homemade – Korg HA-S Nutek

The Korg HA-S Nutekt combines Korg's Nutube tube technology with a DIY build concept. This battery-powered headphone amplifier offers the opportunity to experience the warm sound of a true triode tube in a modern, compact form - and build it yourself from scratch.

Korg's Nutube technology is a specialty in the modern audio world.
It's a truly analog, miniature triode tube that Korg developed in collaboration with Noritake Itron. The Nutube 6P1 works like a traditional vacuum tube – anode, grids and filament – ​​but thanks to its design, it consumes a fraction of the current, operates at low voltage and is more resistant to mechanical stress.

The Korg HA-S Nutekt is a portable headphone amplifier that demonstrates this technology in practice.
As a special feature, it is delivered as a construction kit, where the user assembles the device themselves without soldering.Nutube 6P1 miniature tube Additional information: korgnutube.com

Easy

Korg's Nutekt construction kit looks like a real electronics project at first glance, but in reality it's almost complete.

The main circuit board is pre-assembled and contains all the small components, so the construction does not require any drilling or special tools. The user's main task is to attach and connect the Nutube module with a terminal block, place and secure the circuit board in the case, and install the volume potentiometer knob.

The package contains two circuit boards: the main board and a smaller Nutube module, which is attached with the included connector. Pads are glued under the tube and on the edges to dampen mechanical resonance and prevent microphonics. Also included are capacitors, trimmer potentiometers, an operational amplifier, mechanical parts and a case. All parts are neatly packaged, and instructions can be found both in print and online.

The housing is compact, metallic and elegantly finished. The smoke-gray translucent cover reveals the Nutube's greenish glow during use, which is part of the device's visual appeal. The battery compartment is integrated into the body, and two standard AA batteries are sufficient for power supply.

The assembly process is logical and straightforward, and the finished device can be assembled in about an hour. The construction phase offers enough work for even the less experienced enthusiast, but the end result looks and feels like a fully finished device from the factory.

Structure and adjustment options

The HA-S amplifier stage is therefore based on an op-amp circuit built around the Nutube 6P1 triode. The solution combines analog tube signal processing with modern, low-power electronics. The tube operates on a 26 V anode voltage generated by a small converter, but the total power consumption remains suitable for battery operation.

The user has a few adjustments available with four small trimmers: two bias voltages and two anode resistors, which are used to fine-tune the channel balance and the operating point of the tube.