Get ready to be captivated by an extraordinary project that required long and meticulous refinement work: the SB Nebula OTL tube headphone amplifier. From its humble beginnings with the OTL SRPP and 6080 tubes, we have made an incredible journey toward excellence.
Project evolution
This project has undergone a long process of improvement. Starting from a limited OTL SRPP design using 6080 tubes, we moved to an MJ OTL still based on 6080s. Later, to reduce heat radiation and unnecessary power consumption, the 6080s were replaced with 6BX7s. Only a few issues remained: the excessive weight caused by oversized transformers, a small pop in the headphones during shutdown, and the absence of a PCB, which prevented consistent series production. Those interested in the technical development can click here.
Circuit and components
SB Nebula retains the basic design of its predecessor, but with an extra touch of perfection. We listened to your feedback and made key improvements to deliver an even more exceptional audio experience.
We chose to adopt 12BH7A dual triodes on noval sockets, renowned for their uncompromising audio quality. These tubes are optimally utilized, bringing the sound to new heights of fidelity.
The power transformer has been specially designed for Nebula, reducing total power consumption to just 38 watts compared to the previous 200+. The filament supply is now fully DC, while the anode supply is completely free from ripple thanks to high-grade capacitors and a capacitance multiplier that brings total filtering capacity above 6000uF. This ensures clean, stable energy for clear and detailed sound.
Silence and headphone protection
SB Nebula integrates a digital microcontroller that manages the power-on, preheating, and shutdown phases, ensuring total headphone safety. Background noise has been completely eliminated: during operation or shutdown, no disturbance is audible, even in perfectly quiet environments.
Handcrafted construction
Each SB Nebula is entirely handmade with artisanal care. The solid oak cabinet is selected for its aesthetic and acoustic qualities and internally shielded with a pure copper band connected to ground for safety and protection from electromagnetic interference.
Aesthetic customization
We offer a unique customization experience. The chassis can be laser-engraved with designs or symbols chosen by the customer, crafted in different wood types and finished to order. Each SB Nebula becomes a one-of-a-kind piece, expressing the personality of its owner.
Printed circuit and components
The amplifier is fully designed and built at SB-LAB. I chose to use a high-quality printed circuit board to ensure reliability, repeatability, and consistent performance. Point-to-point wiring, although visually appealing, offers no real advantage unless done flawlessly.
Every component is carefully selected: Nichicon and AudynCAP capacitors, precision resistors, and high-end audio parts. Everything contributes to a musical reproduction that is clear, dynamic, and natural.
Performance and compatibility
The MJ OTL circuit allows Nebula to drive headphones from 32 ohm up to 600 ohm with ease, maintaining perfect balance and dynamics. The frequency response ranges from 10Hz (-0.2dB) to 33kHz (-1dB). The optimal output power is around 35mW, more than enough for high-quality listening while avoiding any risk of damaging the headphones.
THD distortion at 35mW: 2.3% on a 220ohm load.
Tubes installed:
One pair of ECC88/6DJ8 or equivalents
One pair of 12BH7 or equivalents
Price and warranty
The price of SB Nebula, excluding shipping, is €1500. Each amplifier is CE-compliant and supplied with a warranty according to current regulations. The price may vary depending on aesthetic customizations and fluctuations in raw material costs. Those interested in purchasing can contact me through this form.
Open source software
Nebula uses open source software released under the GPL V2 license inside the power control microcontroller. In compliance with the license, the source code is available upon request to customers who have purchased the unit. Anyone wishing to receive a copy can contact me directly through the Contact form. Opening or reprogramming the controller voids the product warranty. The code is provided solely for personal and hobby use.