Vintage Digital & Analogue Studio Effects

Vintage Digital

Electronaut M97

Electronaut M97 Compressor Limiter

The Electronaut M97 is a modern take on an idea that has been evolving for 70 years — a triode amplifier with a variable amplification factor (expressed mathematically as ‘µ’ or ‘mu’), configured to provide dynamic range compression and limiting for high-quality audio.


This compressor is the result of literally thousands of hours of effort studying, experimenting, designing, building, testing, listening, redesigning, rebuilding, retesting, relistening, (insert seemingly infinite loop here), until a compressor finally emerged that seemed refined enough to be worthy of production. The sheer amount of work required to undertake such a project begs the question: does the world really need another monster tube variable-mu1 compressor?

Aren’t there already enough Fairchild clones available?
The answers are unequivocally YES, and YES. The year 2016 marks 110 years since the triode vacuum tube was invented in Chicago in 1906. As we look back over this incredible span of ingenuity, a trend-line immediately reveals a constant incremental progress, with creative thinkers picking up where others left of and pushing things a little bit further, inspired by
limitations they thought could be improved upon. Every single audio equipment designer throughout history benefited from the work done by their predecessors, and the trend
of incremental progress happened because people were driven to look forward and think of new ideas.

The engineers that created the tools we musicians and recordists depend upon generally shared three key things: a willingness to study and learn from the past, a solid understanding of the present, and a creative vision for the future. Something interesting started to happen within the last couple of decades: musicians and engineers began to realize that despite a century of constant progress, many old designs still held their own against new designs, and in a lot of instances the older designs simply sounded better.

One hundred years of constant improvement had also been heavily influenced by 100 years of economic interests, and the result wasn’t always good for the sound. This realization, combined with the emergence of internet auction services and a globally interconnected world, inspired a frenzy of trading in vintage electronics, which in turn inspired a frenzy of manufacturers
issuing ‘clones’ of vintage designs.

Deeply rooted in Electronaut’s philosophy is a belief that audio equipment design should be informed not only by an engineering perspective, but also from a musician’s perspective. If we consider equipment design from a musician’s perspective, some things immediately become clear: cloning other people’s designs from the past is basically the same thing as being in a cover band.

Cloning is an attempt to celebrate the work of people who left behind a legacy that still may have untapped market potential, just as a classic-rock cover band may find paid work playing other people’s songs at weddings or corporate events. There’s nothing wrong with that, and there are many examples of designers who have labored tirelessly to reproduce every detail of a vintage design to exacting standards, flaws and all, just as there are musicians who have labored tirelessly to perfect every riff in the Beatles’ discography. A lot of people really want to hear songs from the past performed live, so naturally someone will step up and provide such an experience. That’s just how the world works.

But the world works in other ways too: people are creative and not everyone is interested in mimicking other people’s original ideas. Many people have their own ideas and a strong desire to actualize them, and that’s the reason we have new music and art and books and movies.

For some people, admiration for the great work of the past reaches a fever pitch, resulting in a belief that these past works are so perfect that they can never be improved upon. Again, viewed from the musician’s perspective, this seems totally absurd: try convincing musicians that they shouldn’t bother to write new music because great music has already been achieved!

The world needs another variable-mu compressor because the variable-mu technique is an amazing idea with a totally unique sound that has stood the test of time, and continues to show new potential even in a vastly different technological world. Simply stated, the idea still works amazingly well, yet there is still plenty of room for improvement.

But does the M97 sound like a Fairchild or not?
The Electronaut M97 is a heavy-duty, single-stage variable-mu compression amplifier with a fast and powerful controlling amplifier, and as such it shares many of the qualities that made the Fairchild’s sound the way they do. However, no attempt has been made to mimic the Fairchild’s limitations. Instead, Electronaut designed a series of improvements that just make sense in a 21st century vari-mu, including:

  • Continuously-variable attack and release controls instead of a small number of fixed time constants
  • Higher-current controlling amplifier providing faster attack and improved peak transient reduction capability
  • Significantly-improved balance calibration method for reduced distortion and thump-free operation
  • Lundahl transformers for improved frequency response and optimal interfacing
  • 24-position balanced bridged-T input attenuator
  • Tube regulated high voltage power supply filtered solely by a large choke and four polypropylene capacitors
  • Vastly superior dB-accurate metering system displaying input and output level, threshold level, gain reduction, 2nd harmonic distortion, and even peak transient reduction!

Ultimately, the important characteristic is the audio circuit topology: the Fairchild was a single-stage variable-mu compressor with a powerful controlling amplifier, and at the time it was arguably the best implementation of that particular technique. What made it such a great sounding compressor was not that it had a magic combination of flaws; what made it great was that it expanded the usability of the variable-mu concept to the extent that it could handle nearly any type of program material – something previous variable-mu compressors, arguably, could not achieve.

One of the main advantages of the single stage approach is an incredibly simple signal path: an input transformer, a tube amplifier, and an output transformer. Not even a single capacitor is present in the signal path. Not all variable-mu compressors are built this way — many currently available designs economize on the vari-mu stage and add additional capacitively-coupled gain stages to make up for it, but this is a move in the direction of a more complex signal path, which in Electronaut’s belief, is fine when necessary but less than ideal.

Simpler is almost always better, and the single-stage variable-mu concept managed to maintain a simple signal path while offering ample control of the audio’s dynamics. Electronaut chose to use this approach as its jumping of point, and to try and hunt down things that could be improved upon, not only in terms of sonics, but in usability, interface, and features.

In Electronaut’s view, the prevailing spirit of pro audio equipment design is the desire to constantly improve, just as a musician may practice for a lifetime to constantly improve. An environment where recordists exhibit a healthy resistance to stagnation and the status quo is better for every musician who ever wants to make a record. We can let the luddites be luddites without criticism or judgement, and remember that they don’t have to stand in the way of new ideas. With this spirit in mind, Electronaut humbly presents the Electronaut M97 Compressor/Limiter.





  • Maximum Gain: Approximately 17 dB
    Frequency Response:

    • (with Input Attenuator set to -6 dB): 20 Hz to 20 kHz +/– 1.3 dB
    • (with Input Attenuator set to 0 dB, Zsource = 100 1): 15 Hz to 53 kHz +/– 1.3 dB
  • Line Input: 600 1 floating transformer balanced
  • Sidechain Input Impedance: 1200 1 floating transformer balanced
  • Line Output Impedance: 120 1 floating transformer balanced, internally terminated by 1800 1
  • Recommended Load Impedance: 10 k1 or higher
  • Minimum Recommended Load Impedance: 600 1
  • Signal to Noise Ratio: > 85 dB
  • Max. Output Level for 1% THD:  (no limiting): +28 dBu
  • THD + Noise at +4 dBu:
    • (no limiting): 0.02%
    • (10 dB limiting): 0.7%
  • Recommended Upper Limit of Compression for High Fidelity: 12 dB
  • Power Requirements: 120V 60 Hz or 240V 50 Hz, 240 Watts MAX
  • Dimensions: 483mm x 356mm x 178 mm)
  • Weight: 15.5 kg

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Electronaut M97

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