L10 input and output amp
module for the
Stellavox TD9 tape recorder

The original L9 IN/OUT module for the TD9 tape recorder was developed at Stellavox towards the end of the 1970s. Signal balancing was carried out using transformers, as was common at the time. These transformers also had the pleasant side effect of galvanic isolation, which is less important today, since TD9 recorders run exclusively as installed units in studios around the world, where ground loops can be excluded by planned and controlled ground flow. What remains, however, are the shortcomings of the transformer: poorer transient behaviour, more distortion and a reduced dynamic. Furthermore, with micro-electronic surface-mount devices (SMD) unavailable at the time, it was not possible to build both original amplifier units with single components (discrete circuit) because of the reduced space.

Looking at the past and at today’s technical possibilities, we came up with the idea of developing a new module for what may well be the world’s best tape recorder. Beating excellence is of course a challenge! However, we believe to have significantly improved the TD9’s reproduction quality by eliminating the bottleneck created by the transformers.

During the development of this newer module, we had to consider another “plus” of the transformer technology in the input section: namely the common mode rejection ratio (CMRR), which is better than that achieved from the usual electronically balanced inputs. After a few attempts, the transformer’s CMRR was actually beaten (min. -80dB). The trick is having a double balanced structure and obviously ultra low tolerance resistors in thin film. The output section is built around a balanced Class-A amplifier. As with any audio electronics developed by Stellavox, we have completely avoided negative feedback. Offset control is ensured through the use of low resonance DC servos (100 mHz), another circuit element developed by Stellavox in recent years.
Since the TD9 recorders that are still running around the world are hardly ever operated with synchronisation, we have dispensed with corresponding circuits in the L10.
Thanks to the use of resistors with 0.1% tolerance and the omission of transformers (which by their very nature bring inaccuracies in gain), the trimmers for gain control were also omitted. The L10 module will keep its gain constant for many decades without the need for frequent trimming.

Josef Sabaini
the new Stellavox ambassador since forever

Josef Sabaini has always been a great supporter of the analogue music world, encountering his first Stellavox tape recorder while still a student. During the summer of 2022, the renowned Austrian violinist and conductor contacted Stellavox SA and immediately became a proud ambassador for the brand, finding it to be the only logical choice for achieving a truly incomparable sound.

The story of Sabaini and Stellavox originally dates from the early 1970s when he and other students would spend time at the house of their teacher, Ricardo Odnoposoff. It was there that Sabaini saw two Revox recorders for the first time, kept in an old baroque trunk, and was fascinated by them. However, the professor confided that he owned something even better, introducing Sabaini to the Stellavox SP7. Sabaini was immediately captivated by the portable tape recorder, but with its price out of reach (even in those days) he had to temporarily put his dream of ownership aside.

Fast-forwarding to the mid 1980s, Sabaini encountered Stellavox for a second time. While in Neuchâtel for a concert, he remembered the Swiss company that appeared to be based there. Visiting the factory he marvelled at the large machines under construction, all of which were being assembled in the same room. However, with prices now skyrocketing, Sabaini had to put his lifelong dream of ownership on hold once more.

Over the following 30 years, with the advent of digital technology, analogue tape recorders lost their value and it was during this time that Sabaini devoted himself to building his collection of analogue recorders, as well as acquiring original masters of classical recordings. Once again Stellavox came to mind and Sabaini managed to obtain a small SM8 recorder. The sound was incomparable, "so clean so... natural!” Sabaini therefore felt compelled to complete his collection with a TD9 "the king of tape recorders".

In 2022, while searching for a head block for his TD9, Sabaini stumbled upon the Stellavox SA website and discovered the new L10 module. Full of excitement, he called the company headquarters and talked at length with Stephan Schertler. Fascinated by the company's apparent “second life”, Sabaini immediately travelled to Switzerland, bringing his original master recordings with him. He and Stephan listened to these via the L10 and it was during a recording of David Oistrakh that Sabaini observed “for a violinist it is always a stylistic criterion to be able to understand a note written on which string it is played. Thanks to the L10, I was able to perceive the complete finger setting”.

Even more amazing was the fact that while listening to a theme whistled by Livingstone Taylor, they could hear the whistle so clearly that it was possible to distinguish air passages, which, in real life, could only be perceived by the person who was whistling.

Sabaini was thrilled. The L10 was not just an improvement, but also something innovative, with a crisp, transparent and light sound, capable of arousing a visceral emotion in the listener. "This is something new for me," he enthused, never having heard a level of precision that was capable of giving each sound and instrument its exact space.

“It's like the role of the conductor. To some outsiders the conductor seems superfluous, standing there in front of a huge orchestra. Yet, the musicians move following a flow that the conductor must be able to create and lead. There is room in that flow for each individual voice, defined, precise, and at the same time all the voices are part of a single, light unit. The same happens when, with your eyes closed, you listen to a piece through the L10.”

Josef Sabaini has finally found the sound that, during 50 years of research, he had never been able to hear. Now, with Stellavox, everything is back where it belongs.