Introduced in 1994, the Aphex Model 107 Tubessence represented the company’s entry into a new generation of hybrid microphone preamplifiers. Rather than following the established approach of using high-voltage valve stages or entirely solid-state electronics, Aphex developed a circuit that combined the operational advantages of both technologies. The result was a compact, affordable two-channel preamplifier that brought genuine valve circuitry into recording environments where traditional valve equipment might have been considered impractical or too expensive.
The central innovation of the Aphex Model 107 was its proprietary Tubessence circuitry, built around a technology Aphex called the Reflective Plate Amplifier (RPA). This patented approach allowed a valve to operate at approximately 1V RMS, considerably lower than the voltages normally associated with conventional valve amplifiers. The circuit was developed to retain desirable characteristics of valve amplification while avoiding the excessive heat, high-voltage requirements and shortened component life associated with some traditional designs.
Unlike many hybrid preamplifiers that simply introduce a valve into an otherwise conventional solid-state signal path, the Model 107 was designed around the interaction between its transistor input stage and the Tubessence circuit. Its transformerless front end employs matched transistor circuitry, with the microphone signal passing through a carefully designed solid-state amplification stage before reaching the valve circuitry. High-quality capacitors were selected for the signal path, while the absence of an input transformer eliminated the frequency response and phase characteristics associated with transformer-coupled designs.
The Tubessence stage uses a single 12AT7/ECC81 dual-triode valve, shared between the two independent microphone channels. Aphex designed this arrangement to produce valve characteristics while maintaining low noise, low distortion and extended component life. The relatively low operating voltage also reduced internal heat generation, allowing the preamplifier to be housed in a compact 1U rackmount enclosure without the substantial power supply and ventilation requirements of conventional high-voltage valve equipment.
Each channel provides continuously variable microphone gain, with an overall amplification range from +18dB to +64dB. Engaging the 20dB input pad changes the available range to -2dB through +44dB, allowing the preamplifier to accommodate high-output microphones and particularly loud sound sources. This flexibility made the Model 107 suitable for a wide variety of recording applications, from low-level acoustic instruments and vocals to close-miked percussion and amplified instruments.
The front panel features individual microphone inputs on locking three-pin XLR connectors. Aphex deliberately positioned these connections on the front of the unit to keep the sensitive low-level microphone circuitry physically close to the input connectors, reducing the length of internal signal paths. This arrangement also made microphone connections convenient when the preamplifier was installed in an equipment rack.
Each channel includes independently switchable 48V phantom power, allowing the Model 107 to operate with condenser microphones requiring external power while also accommodating dynamic and ribbon microphones when phantom power is disabled. A dedicated red LED indicates phantom power activation, providing a clear visual indication of the channel’s operating condition.
A switchable 80Hz low-cut filter provides attenuation at 12dB per octave, allowing low-frequency disturbances such as microphone handling noise, wind noise and mechanical rumble to be reduced before recording. This facility was particularly useful for vocal recording, location work and applications where unwanted low-frequency energy could otherwise consume available headroom. Each channel also includes a polarity inversion switch, allowing the microphone signal to be electrically inverted by 180 degrees to address polarity differences arising from microphone placement or cabling.
The Model 107 incorporates individual signal-level indicators for each channel. A green OK LED provides confirmation of the incoming signal level, while a red Overload LED warns when the signal approaches clipping. These indicators allow the operator to establish appropriate gain settings without requiring a separate meter or monitoring system.
An additional feature is the remote muting facility provided independently for each channel. Rear-panel 6.35mm TS sockets accept an external contact-closure switch, such as a footswitch, allowing the microphone signal to be muted remotely. A corresponding red front-panel LED illuminates whenever the channel is muted. This arrangement was particularly suited to live performers, broadcasters and recording applications where the microphone user needed direct control over signal muting.
The rear panel also incorporates individual output-level selectors, allowing each channel to operate at either +4dBu or -10dBV nominal level. This enabled the preamplifier to interface with professional recording consoles, digital recorders and other equipment operating at different reference levels. The outputs use a single-ended, impedance-balanced configuration, sometimes described as quasi-balanced, presented on 6.35mm TRS sockets.
This output arrangement provides many of the noise-rejection advantages of balanced interconnections when connected to a balanced receiving input. Unlike a conventional differential output, however, the negative conductor carries a ground reference rather than an inverted audio signal. The outputs can also be connected to unbalanced equipment without the signal loss associated with some conventional balanced output arrangements.
The published frequency response of the Aphex Model 107 extends from 20Hz to 20kHz, with an equivalent input noise specification of -128dBu at maximum gain. The input circuitry provides common-mode rejection exceeding 70dB at 60Hz, while the preamplifier’s audio path was designed to maintain low noise and distortion across its operating range. These characteristics allowed the Model 107 to be used as a primary microphone preamplifier rather than simply as an optional valve-colouring device.
For multitrack recording, the Model 107 could be used to bypass a recording console’s internal microphone preamplifiers, feeding the output directly to a recording device or mixing system. This arrangement provided an alternative signal path for critical sources such as lead vocals, acoustic instruments and stereo microphone recordings. The availability of two matched channels also made it suitable for stereo recording techniques, including coincident and spaced microphone arrangements.
The Model 107 was equally applicable to broadcast, film production and location recording. Its compact construction, transformerless circuitry and external power supply made it suitable for portable recording systems, while the remote muting capability provided a practical advantage in live performance and presentation environments.
The Aphex Model 107 Tubessence attracted attention following its introduction, appearing in professional recording publications during 1995. Its hybrid circuit design was recognised for combining valve and solid-state technologies in a relatively inexpensive microphone preamplifier. The Model 107 also received a TEC Award in 1995, marking an important achievement for Aphex’s microphone preamplifier development.
The Tubessence technology subsequently became an important part of the company’s microphone preamplifier range. Aphex later developed the Model 207, which retained the underlying microphone input and Reflective Plate Amplifier concepts while introducing additional facilities and revised circuitry. Production of the Model 107 was discontinued following the development of its successor.
The Aphex Model 107 Tubessence remains a distinctive example of 1990s hybrid microphone preamplifier design. Its combination of transformerless solid-state input circuitry, low-voltage valve amplification, comprehensive microphone controls and practical studio connectivity illustrates Aphex’s approach to making valve-based recording technology accessible to a wider range of professional and project recording environments.
Features
- Two independent microphone preamplifier channels.
- Proprietary Aphex Tubessence valve amplification circuitry.
- Patented Reflective Plate Amplifier technology operating at approximately 1V RMS.
- Hybrid solid-state and valve design using a 12AT7/ECC81 dual-triode valve.
- Transformerless, active balanced microphone input circuitry.
- Up to 64dB of microphone amplification.
- Continuously variable gain control for each channel.
- Switchable 20dB input pad with LED indication.
- Independent 48V phantom power with LED indication.
- Switchable 80Hz low-cut filter with 12dB per octave slope.
- Individual 180-degree polarity inversion switches.
- Green signal OK and red overload LED indicators.
- Front-panel locking XLR microphone inputs.
- Independent remote muting for each channel using external contact-closure switches.
- Dedicated remote mute LED indicators.
- Selectable +4dBu or -10dBV nominal output levels.
- Impedance-balanced outputs on 6.35mm TRS sockets.
- External 24V AC power supply.
- Compact 1U rackmount enclosure.
- Designed for studio recording, broadcast, film production and live sound applications.