Virtual Valve Amplifier
Encyclopedia
A Virtual Valve Amplifier (aka. VVA) is a modern software development for simulating the sound of various valve amplifier
designs that would normally consist of valves/electron-tubes
.
A VVA can be used to color the sound of a digital recording by adding "tube-warmth" in addition to adding subtle harmonics to enhance very old or muffled recordings. The algorithms behind a VVA are based on real vacuum tube circuits and vacuum tube non-linear device characteristics through mathematically deriving the “large-signal” transfer functions of various vacuum tubes and output transformers found in vauum tube amplifier designs. A majority of this data was originally derived from extensive bench measurements of real vacuum tube amplifier circuits under varying operating conditions by engineers Craig Maier and Rick Carlson in the early 1990s. As such, the effects of a VVA are a direct mathematical reconstruction of the same signal passing through a physical electron tube amplifier.
that is generally incorporated into an RC coupled class A audio pre-amplifier configuration and its design is optimized to minimize harmonic distortion. This vacuum tube is still the industry standard pre-amplifier valve. It has a relatively flat linear operating region in the middle of its dynamic operating range, producing relatively lower levels of distortion compared to some of the other devices listed here. But, by moving the Operating Point to either the saturation of cutoff extreme, more “tube-warmth” effect can be produced by this device. This is the same device as the European type ECC83.
and its equivalents are often found in high-gain vacuum tube microphone amplifiers which require the sharp-cutoff of a pentode. It generally produces a very pleasant “tube-warmth” effect when the operating point is properly set. This device is the same as the European type EF183.
were important. Its high-gain characteristics and family of operating curves make for useful harmonic distortion and signal compression properties.
who reportedly used this amplifier configuration to cut all the records made from his home studio.
Valve amplifier
A valve amplifier or tube amplifier is a type of electronic amplifier that makes use of vacuum tubes to increase the power and/or amplitude of a signal. Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by solid state amplifiers during the 1960s and...
designs that would normally consist of valves/electron-tubes
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
.
A VVA can be used to color the sound of a digital recording by adding "tube-warmth" in addition to adding subtle harmonics to enhance very old or muffled recordings. The algorithms behind a VVA are based on real vacuum tube circuits and vacuum tube non-linear device characteristics through mathematically deriving the “large-signal” transfer functions of various vacuum tubes and output transformers found in vauum tube amplifier designs. A majority of this data was originally derived from extensive bench measurements of real vacuum tube amplifier circuits under varying operating conditions by engineers Craig Maier and Rick Carlson in the early 1990s. As such, the effects of a VVA are a direct mathematical reconstruction of the same signal passing through a physical electron tube amplifier.
Basic Operating Parameters
VVA designs generally include a number of parameters that may be configured to change the sound and operating characteristics of the amplifier design:Operating Point
Historically referred to as the “Q” or bias point by engineers, the operating point of a vacuum tube is a condition generally fixed by the amplifier manufacturer. In general, the operating point determines the device’s bias value at zero signal input and determines the distribution of harmonics introduced into the output of the amplifier. Tubes that operate with a higher operating point close to "cutoff" give more "headroom" enabling greater volume gains to be applied before signal degradation in the form of "break up" or saturation results. By contrast, a lower operating point introduces more harmonic modification into the final output as a result of the different non-linearity distribution near cutoff as compared to operation near saturation. Some instrument amplifier users such as guitarists use this phenomenon for its sound effect.Drive
This describes how loudly the “physical” equivalent of the virtual valve amplifier is set. However, the output level of a VVA generally remains constant independent of drive due to internal gain compensation algorithms. Instead, the drive determines the amount of distortion that can be introduced into the output signal. As such, the Drive of a VVA describes the degree of modulation applied to a given vacuum tube amplifier circuit centered about the set operating point. The higher the drive level setting, the greater will be the production of predominantly even order harmonics due to the circuit’s asymmetrical non-linearity. As a result, the VVA “effect” increases with increasing drive.Triode (12AX7)
This is a high-mu dual triodeTriode
A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device...
that is generally incorporated into an RC coupled class A audio pre-amplifier configuration and its design is optimized to minimize harmonic distortion. This vacuum tube is still the industry standard pre-amplifier valve. It has a relatively flat linear operating region in the middle of its dynamic operating range, producing relatively lower levels of distortion compared to some of the other devices listed here. But, by moving the Operating Point to either the saturation of cutoff extreme, more “tube-warmth” effect can be produced by this device. This is the same device as the European type ECC83.
Triode (12AT7)
The 12AT7 high-mu dual triode was designed primarily for RF mixing applications where it was incorporated into the oscillator/mixer stage and used to heterodyne incoming RF signals with the local oscillator to create an intermediate frequency in TV and FM sets. Thus, it is intentionally designed to be extremely non-linear. Thus, circuits based around the 12AT7 exhibit a larger degree of non-linearity throughout the entire dynamic operating range, including the middle. As a result, it produces a greater even order harmonic distortions (the most pleasing harmonic distortion). This is the same device as the European type ECC81.Triode (12AU7)
The 12AU7 is a medium-mu dual triode often found in the driver / phase inverter stage of a push-pull power amplifier and also results in significant non-linearity in the middle of its dynamic operating curve.Pentode (6EJ7)
The 6EJ7 pentodePentode
A pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid vacuum tube , which was invented by the Dutchman Bernhard D.H. Tellegen in 1926...
and its equivalents are often found in high-gain vacuum tube microphone amplifiers which require the sharp-cutoff of a pentode. It generally produces a very pleasant “tube-warmth” effect when the operating point is properly set. This device is the same as the European type EF183.
6267 / EF 86 Pentode
The 6267 / EF86 pentode was a vacuum tube well suited for use in low-level preamplifiers where low noise and minimal microphonicsMicrophonics
Microphonics describes the phenomenon where certain components in electronic devices transform mechanical vibrations into an undesired electrical signal...
were important. Its high-gain characteristics and family of operating curves make for useful harmonic distortion and signal compression properties.
2-Stage Class A Vacuum Tube Amplifier
These devices generally consisted of a 12AU7 medium-mu triode driving a single 6L6GC beam power pentode audio output valve or similar. Its effects are distinctive due to convolution of the non-linearity of the triode interacting with those of the pentode, with both devices operating in class-A mode. The 6L6GC is similar in performance to the industrial type 5881, and also the European type KT-66.2-Stage Class AB Vacuum Tube Amplifier
Often consisting of a 12AU7 phase inverter / driver, pushing a pair of 6L6GC beam power pentodes. Because the circuit is push pull, the output devices produce a more symmetrical and reduced even-order distortion characteristic distribution. The operating point is fixed at the factory, and cannot be adjusted for this amplifier configuration.2A3 Push-Pull Vacuum Tube Amplifier
Also known as a “retro – triode” amplifier, it was invented in the 1930’s and incorporated a directly heated cathode resulting in a high power output. It was often found used in theatrical applications and public address systems. This vacuum amplifier typically exhibits a more linear output transfer characteristic compared to its Pentode push-pull counterpart and as a result produces a unique characteristic clean sound. The particular devices that we used to create the 2A3 VVA models were of the “dual – plate” variety taken from new (unused) stock manufactured for the military by RCA Victor in 1953. This configuration is also favoured by many jazz musicians including Les PaulLes Paul
Lester William Polsfuss —known as Les Paul—was an American jazz and country guitarist, songwriter and inventor. He was a pioneer in the development of the solid-body electric guitar which made the sound of rock and roll possible. He is credited with many recording innovations...
who reportedly used this amplifier configuration to cut all the records made from his home studio.