When an amplifier becomes something truly unique. Some projects begin as simple commissions, while others slowly evolve into something far more personal. Aurelion unquestionably belongs to the latter category.
This project was born from a very specific request: to create an unconventional single ended amplifier built around extremely rare historical tubes, with intentionally minimal output power. An amplifier designed for late-night listening sessions, bedroom systems, and low-volume enjoyment, while still preserving all the sonic magic that only certain minimalist circuits can deliver. And honestly, these are exactly the kinds of projects that truly excite me.
The Meaning Behind the Name Aurelion
The name Aurelion was conceived as an epic and fantasy-inspired reinterpretation of the Latin name “Aurelio”, itself derived from “aureus”, meaning “golden” or “shining”. It does not refer to any real star, yet it evokes something luminous, celestial, majestic, and almost cosmic. A name intended to suggest light, elegance, energy, and visual presence, while still maintaining a connection with classical Latin roots.
Even the symbol engraved on the front panel follows the same philosophy. A central eye surrounded by a radiant star and astronomical references. The eye symbolizes vision, perception, and awareness, while the star represents energy and light. Together they create a deliberately mysterious and elegant image, perfectly aligned with the character of the amplifier itself.
A Single Ended Amplifier from Another Era
Aurelion uses 843 tubes as output devices, indirectly heated triodes originally developed for telephone applications during the first half of the 1920s. These are tubes that are virtually unknown in the modern audio world, yet absolutely fascinating from both historical and technical perspectives.
For the driver stage I selected 24A tubes, generally considered the first true modern tetrodes. These also date back to the first half of the 1920s and represent one of the earliest evolutionary steps beyond the classic triode. I also discussed the 24 tube family in this article. To stabilize the screen grid supply of the 24A tubes, I used an 85A2 neon gas regulator, while rectification is handled by a 5U4GB.
An Amperite 6N030 thermal delay was also included to postpone the application of high voltage without relying on modern timer circuits.
Despite the extremely low current requirements of the 843 tubes, a 5U4GB rectifier still proved necessary in order to keep operating voltages within manageable limits. The 843s operate at roughly 500V into a load of approximately 12kohm. Final output power is intentionally very low, around 1.6W RMS nominal.
That may sound ridiculously low by modern standards, and in many ways it is. But this amplifier was never designed to “play loud”. It was specifically created for intimate and relaxed listening sessions with high-efficiency loudspeakers, prioritizing delicacy, microdynamics, and tonal presence above sheer volume.
Output Transformer Design
As often happens with my projects, everything started from the output transformers. In this particular case, the combination of extremely low power and very high primary impedance made double C-core construction especially suitable. For this reason I decided to adopt the “2C” technique used in many classic McIntosh transformers.
To achieve this, I designed and 3D printed a dedicated resin bobbin developed specifically for this amplifier. The transformers were then hand wound using carefully selected materials and highly meticulous construction techniques.
Once completed, the transformers were resin impregnated and installed inside soft iron enclosures. These housings are not merely mechanical supports, they also help shield stray magnetic fields. Details like these are rarely visible from the outside, yet they are an integral part of the SB-LAB construction philosophy.
Chassis, Mechanics and Construction
For the external appearance, the amplifier was built using a wooden chassis designed to match Neutrino, the preamplifier intended to partner this power amplifier. Aurelion is in fact a pure power amp, with no volume control and no input selector.
I then produced the aluminum panels, handling drilling and finishing personally, machined the bakelite mounting panel, and completed the full assembly of the amplifier. As always, every part was handcrafted individually, without relying on standardized industrial solutions.
From a circuit design perspective, I deliberately chose not to use global negative feedback. Aurelion operates in an extremely direct and minimalist way, keeping the signal path as clean and simple as possible.
The only feedback present is a very light type-1 shade feedback applied locally, totaling an almost irrelevant 1.25dB. Such a low amount does not perceptibly alter the sonic character of the amplifier, nor does it compromise its dynamics or tonal naturalness. What it does provide is a small degree of compensation for the inevitable construction tolerances found in tubes manufactured nearly a century ago.
This was therefore more of a technical refinement than a corrective measure, implemented not to chase laboratory numbers, but to achieve greater operational consistency while preserving the original sonic personality of the project.
Measured Performance
Final measurements are as follows:
- Clean output power: 1.7W RMS
- Maximum full clipping power: 2.5W
- Damping factor: 2.2
- Excellent square wave response
- Frequency response: 10Hz – 70kHz (-1dB)
THD
Bandwidth
Square Waves 100Hz / 1khz / 10khz
On paper, these numbers may appear almost insignificant compared to modern standards, yet they reveal very little about the true personality of this amplifier. Aurelion was never created to impress through brute power. It was created to build atmosphere.
It is one of those projects that would make very little sense as a mass-produced product, and precisely for that reason it perfectly represents the spirit of SB-LAB: building unique, timeless devices without compromise and without chasing commercial trends.