March 21, 2023
Using vacuum tubes for more natural sound - why & how

Linear devices like vacuum tubes produce a far more natural sound and provide a much deeper emotional connection to the music. But why is that so? Read about the technology.

Linear devices like vacuum tubes produce a far more natural sound and provide a much deeper emotional connection to the music.

Vacuum tubes, also known as thermionic valves or electron tubes, are devices that use a vacuum to amplify or switch electronic signals. They were widely used in a variety of electronic devices in the 20th century, including radios, televisions, and computers, but they are also used in some types of musical equipment, such as studio equipment and guitar amplifiers.

In an amplifier, vacuum tubes are used to amplify a small signal (such as from audio input or from guitar's pickups) to a level that can be processed in a circuit or heard through a speaker. The tubes work by allowing a small current to flow through a heated cathode, which releases electrons into a vacuum. These electrons are then attracted to an anode, where they flow through a grid and are amplified before being sent to the speaker.

In a recording studio, vacuum tubes can be used in a variety of ways, such as in the preamplifiers of microphones, the input stages of equalizers, and the compressors and limiters of dynamics processors. Vacuum tubes can add warmth and character to the sound of a recording, as they introduce subtle distortions and colorations that can give a musical signal more depth and complexity.

While vacuum tubes have largely been replaced by solid-state electronics in most electronic devices, they are still popular in some circles for their unique tonal characteristics and are often used by musicians and audio engineers who want to add a vintage or retro vibe to their music.

The warmth of Vacuum tubes can be partly attributed to the increase in even harmonics of a signal. Harmonics are a way of describing distortion in relation to the input signal.   Many describe even harmonic distortion as ‘less aggressive’ and ‘rounder’ than odd harmonics. Furthermore, changing the biasing circuitry of the tube the magnitude of harmonics can be adjusted.




A vacuum tube works as an amplifier because of its thermionic control characteristics. Vacuum tubes modulate a stream of electrons that flow from the tube cathode to the tube plate by impressing a control voltage on the tube grid.

Vacuum Tubes: Advantages
  • Superior sound quality.
  • Highly linear without negative feedback, especially small-signal types.
  • Smooth clipping is widely considered more musical than transistors.
  • Harmonic control can be obtained through change in bias voltage.
  • Tolerant of large overloads and voltage spikes.
  • Characteristics highly independent of temperature, greatly simplifying biasing.



The innovative FT1 freqtube product from Freqport utilizes multiple high quality vacuum tubes in a unique controllable analog circuit that amplifies and modifies the harmonic characteristic of the signal passing through it.