Instrument Amplifiers

Abstract

This patent describes the concept and implementation of an audio amplifier with the special capability of driving speakers with analog circuits without generating electroacoustic noise due to sound and heat propagation through circuit component materials in the presence of an audio signal. Its highly resistant structure to electromechanical stresses reduces the generation of such noise, and appropriate circuitry can even counteract residual effects. Compared to prior art, the invention significantly improves sound quality, giving musicians greater freedom of tonal exploration and improved ease of performance. Similar improvements are observed when using the invention to drive speakers in music production studios, and in any application requiring the highest sound quality.

Description

[Technical Field]

[0001] The embodiments herein relate to amplifier and preamplifier concepts for audio frequencies, particularly those suitable for driving musical instruments such as electric guitars, and speakers in music production studios. In general, any electronic device design requiring uncompromising sound quality standards can benefit from the present invention. [Background technology]

[0002] Experts in the field of audio amplifiers generally believe that to make the signal coming from an instrument pickup or microphone more pleasing to the ear, a certain level of distortion is necessary. In fact, hi-fi amplifiers with very low distortion rates measured with instruments are often deemed unsuitable for instruments because their tone and harmonics sound cold and "burned out." As a result, guitarists have continued to favor older vacuum tube amplifiers ever since more reliable, hum-free transistor amplifiers began to replace them. RO Ham, "Tubes Versus Transistors," 43rd Annual Audio Engineering Society Convention, New York, September 14, 1972. According to the latter work, psychological subjectivity influences lead listeners to perceive the type of sound produced by overly perfect solid-state devices as unpleasant and unnatural. This is because the resulting distortion rate of vacuum tubes is perceived as too low. Therefore, experts believe there are no real objective technical problems to be solved with audio amplifiers. This is because early devices suitable for cinemas and electric guitars already had the so-called beneficial effect of producing the necessary euphonic distortion, simply by chance.

[0003] This has resulted in decades of patents focused on emulating vacuum tube characteristics. For example, Quilter's "Guitar Amplifier", US Patent No. 20130136278A1 (2013), Hummel's "Vacuum Tube Amplifier Unit", US20150170627A1 (2015), N. Gallo's "Method and Apparatus for Audio Signal Distortion and Vacuum Tube Amplifier Emulation", US Patent No. 20080218259A1 (2008), "Guitar Amplifier", Quilter's US Patent No. 20130136278A1 (2013), e "Vacuum Tube Amplifier Unit", US20150170627A1, Hummel's (2015), "Semiconductor Amplifier with Vacuum Tube Amplifier Characteristics", US Patent No. 20130136278A1, Eric K. Pritchard's US Patent No. 4809336A (1987), "Vacuum Tube Audio "Solid-State Audio Amplifier Emulating a Vacuum Tube Compression Effect," U.S. Patent No. 5,467,400A to Bruce Keir; "Solid-State Circuit for Emulating Vacuum Tube Compression Effect," U.S. Patent No. 5,524,055A to Jack C. Sondermeyer; "Solid-State Emulation of a Vacuum Tube Audio Power Amplifier," U.S. Patent No. 5,636,284A to E.K. Pritchard (1994); "Adjustable Distortion Guitar Amplifier," U.S. Patent No. 4,495,640A to Douglas R. Frey (1982).

[0004] Similar issues are also being addressed in the field of so-called high-end audio amplifiers. Unlike hi-fi amplifiers (which have measured near-zero distortion), these amplifiers are designed based on empirical recipes aimed at mimicking the harmonic distortion patterns measured in amplifiers that ordinary people consider optimal for listening. Examples include Karsten, "Amplifier and Preamplifier Circuits" (2001, U.S. Patent No. 6,242,977 B1), and Berry, "High-Fidelity Floating Bridge Amplifier" (2002, U.S. Patent No. 6,747,513 B1). In summary, the prior art typically devised audio amplifiers that applied specific modifications to the input signal to enhance sound quality, resulting in a kind of euphonic veil. According to the prior art, the origin of this kind of beneficial distortion lies in the characteristics of electric valves. While solid-state devices have attempted to perfectly emulate these characteristics, guitarists still prefer amplifiers based on early vacuum tube circuits. This means that the prior art approach is missing something essential—something that cannot be detected by today's measuring equipment. Therefore, the prior art belief that the evaluation of an amplifier's sound quality is determined solely by psychological / subjective factors, rather than technical / objective factors, is merely speculation and has not been substantiated in practice.

[0005] The explanations presented in this paper that remain unresolved in the prior art are as follows: i) Vacuum tubes and appropriate types of electronic components and circuits are weaker sources of electroacoustic (or anti-harmonic) noise. This phenomenon will be explained later in this paper, but its existence is ignored in the prior art. ii) To improve sound quality, it is necessary to remove all types of distortion and noise, including the aforementioned distortions, rather than adding some kind of euphonic distortion to the audio signal. Therefore, it can be said that the problem of sound quality in audio amplifiers is unresolved in the prior art.

[0006] To understand the novelty described here, consider the typical electrical circuit diagram in Figure 1, which is for a well-established prior art guitar amplifier that essentially replicates a vacuum tube amplifier from over half a century ago. Guitar amplifiers typically require distortion devices to appropriately alter the sound coming from the pickups to suit the musician's expressiveness and artistry. This alteration can be produced by squaring the waveform, introducing reverberation effects (obtained with appropriate springs), or other methods, artificially adding harmonic content to the instrument's signal. In any case, when a sound is distorted by natural or artificial causes, electroacoustic noise significantly alters the sound's characteristic harmonic patterns, determining its individuality. However, this type of noise becomes part of the sound produced using conventional equipment and cannot be controlled or eliminated by the performer. As a result, the sound is reproduced in a highly standardized manner, losing its individuality and originality. This is precisely the effect of electroacoustic noise, which restricts the performer's freedom to create the sound they desire based on the harmonic richness of the music.

[0007] In Figure 1, the signal from the instrument pickup is transmitted in a single configuration (unbalanced) from the input to the output stage (see modules U5a and U5b). The diagram also shows the output stage, which includes a push-pull device that powers the output transformer. The diagram also shows the circuit components used to adjust the gain and volume (master) respectively, and the tone controls for each channel, which are designed to produce different sound modes (clean or distortion). An important feature of all top quality traditional guitar amplifiers (reminiscent of early vacuum tube electronics) is that their voltage amplifier stages are cascaded in a common cathode ("white cathode") configuration, as shown in Figure 2. See also U1a (general purpose preamp) and U2a (CH1 voltage amplifier stage) shown in Figure 1.

[0008] Another technical solution commonly used in the prior art is the use of semiconductor switches in the signal path to the amplifier module containing device U2a (see Figure 2). Furthermore, metal-film, carbon-composite, or plastic-film resistors and potentiometers are commonly used in electronic circuits, which have the advantage of reducing electromagnetic noise pickup by the power supply. Furthermore, the prior art does not provide specific suggestions regarding the structural characteristics of capacitors or active elements (valves). When manufacturers claim to offer special, handcrafted products and to use specialized components, they typically do not justify their choices. These choices appear to be driven solely by commercial considerations. These choices are consistent with a deeply held belief among experts in the field of audio amplifiers that achieving the sound quality musicians desire requires satisfying a certain emotional response, rather than addressing technical flaws that ultimately affect the circuitry.

[0009] Additionally, the way the speakers are driven is also important, because traditional guitar amplifiers must be "full-band" amplifiers. Therefore, traditional tube amplifiers are equipped with output transformers that drive one or more speakers through the same pair of output terminals on the guitar amplifier. Only bass guitars (commonly referred to simply as "bass") may drive two-way speakers. This means that the speakers have at least one dedicated low-frequency speaker and at least one dedicated high-frequency speaker, with the crossover frequency typically set at around 2 kHz by a passive crossover network.

[0010] Disclosure of the Invention Unlike the prior art, the present invention embraces the idea that electronic circuits truly useful for the highest quality sound reproduction do not add artifacts of any kind to the audio signal. Artifacts include not only those that, according to the prior art, result in euphonic effects, but also physical variations that do occur but whose existence is ignored by the prior art because they are not captured by instrumental measurements. However, such measurements are unrelated to the enormous richness and complexity of the harmonic content that characterizes even trivial audio signals. The task therefore became to carry out comparative listening tests between standard equipment and a prototype designed to implement the invention. The results are reported here to demonstrate the objective factors that actually determine the sound quality differences in audio amplifiers. The tests were carried out using as input signals generated directly by instrument pickups or microphones, rather than recorded sounds, even if of high quality. In fact, the latter would in any case be subject to electro-acoustic noise due to the electronic chains used in the recording.

[0011] Amplified instruments, like guitars, are often played using distortion devices. Musicians often want to alter the signal from their instrument so noticeably that it becomes almost indistinguishable from the original signal. However, these intentional changes must be under the musician's control. Anti-harmonic noise, inherent in conventional electronics, is an artifact that the musician cannot control. Therefore, musicians can greatly benefit from this invention, because, unlike conventional devices, any kind of artificial change to the original signal is under the musician's complete control. This means that musicians should not submit to any kind of acoustic standardization imposed by electronic devices. Therefore, performers will not be subject to any modifications made with the aim of improving the perceived sound quality, as the prior art claims to impose on high-end audio equipment. The resulting nature of homologation would certainly be in conflict with the essential requirement of musicians' freedom of expression. Such freedom cannot be respected, since all prior art devices are affected by electroacoustic noise anyway. To eliminate the annoyance caused by such noise, manufacturers typically attempt to mask it (ignoring its existence) with so-called euphonic distortion.

[0012] This invention solves these problems and meets the real needs of musicians with a new acoustic standard that is free from i) any kind of distortion measured in the equipment, and ii) types of noise not foreseen in the prior art (but which can be easily detected by the human ear by comparing the invention with similar prior art devices). Electroacoustic noise, or antiharmonic noise, is a new concept in physics discovered by this invention. This noise is inherent in circuit components and is the result of electromechanical stresses that occur at a microscopic level in the materials that make up the circuit components through which the audio signal crosses. Even a trivial audio signal is composed of a vast number of harmonic components that give it its sonic signature. This noise arises from the interaction of the signal's harmonic components with phonons, the natural pathways along which sound and heat propagate through the circuit component materials. Using a circuit topology that provides a high common-mode rejection ratio is the primary requirement for suppressing electroacoustic noise. Therefore, it is useful to consider only differential circuit topologies. It is also necessary to connect the amplifier directly to the speakers without a passive crossover network. The following references address similar issues, but do not suspect the existence of antiharmonic noise:

[0013] Rozemblit, in US Patent No. 5,604,461 (1997), discloses an audio power amplifier connected to a long-tail pair circuit preamplifier and an output buffer / bias stage. The output buffer / bias stage has an output terminal for connecting to a speaker. Quilter, in US Patent No. 2013 / 132678 A1, discloses a guitar amplifier with a solid-state module that provides buffering, equalization, and gain control and simulates the overdrive distortion of a vacuum tube amplifier stage (through clipping and power sagging effects). Robling, in US Patent No. 9,306,510 B1, discloses an amplifier that combines a solid-state and vacuum tube dual amplifier with a two-way crossover designed for direct connection to a speaker. Malcolm shows how a floating bridge setup can be used to improve audio amplifier design in "Pontoon Amplifier constructions incorporated error feedback location of floating power suppliers", AES, 60 East 42nd Street, Room 2520, New York 10165-2520, USA, and Berry shows a floating bridge amplifier including a long-tail pair amplification stage in US 7.187.233 B1 (2007). Further examples of related patents include "Differential Input Amplifier Circuit" U.S. Patent 4272728A by HA Wittlinger, "Differential Amplifier" U.S. Patent 2010 / 001797A1 by K. Ishiguro and Y. Takahashi, and "Audio Signal Amplification" U.S. Patent 2008 / 008335A1 by DJ Mate.

[0014] The technological choices made to solve the problem posed here are counterintuitive to those skilled in the art. All resistors, even those not located in the signal path, are wirewound, even if they dissipate little power. These components have no support structures to enhance heat dissipation. In fact, it is the larger resistive element that is key to reducing electroacoustic noise. The elimination of ancillary structures and materials to enhance heat dissipation allows for smaller size, weight, and cost savings. Film-type resistive elements are prone to electroacoustic noise generation. Circular cross-sections have an inherently high mechanical rigidity, which reduces electroacoustic noise generation throughout the structure.

[0015] Wirewound resistors are known to be highly susceptible to electromagnetic noise from the power supply. This problem is solved by using polarized wirewound resistors, which have a clearly marked winding direction. A specific resistance value can be achieved by connecting one or more pairs of resistors in series, side by side with opposite polarity. As a result, the resulting component is non-inductive and less expensive to manufacture. In this case, the cross-sectional area of ​​the resistive element is even larger than if a single component with twice the resistance were used, which has the advantage of reducing electroacoustic noise. In fact, the greater the mass of the resistive element, the lower its noise-generating capability. This is because greater mass also increases resistance to electromechanical effects. The thicker the resistive element, the more sensitive its noise suppression effect. Thicknesses of more than ten-thousandths of a millimeter are acceptable. The optimal solution is a thickness of 0.03 millimeters or more.

[0016] Furthermore, contrary to the belief that electroacoustic noise is actually only present along the audio signal path, due to the diffusive nature of sound and thermal propagation in circuit component materials, electroacoustic noise actually spreads throughout the circuit, reaching parts not along the signal path such as power supplies, constant current sources, etc. Using capacitors with the right construction characteristics (see below) can prevent noise from spreading at the amplifier output. It is also counterintuitive that the output stage must be implemented in solid state rather than Class A as is commonly expected in the HiFi audio field. See, for example, Bongiorno, "Audio Amplifier," U.S. Patent No. 4,229,706A (1980). To reduce electroacoustic noise, solid-state output devices operate in Class AB, biased at a relatively low current so as not to overly amplify the noise of the output device. Furthermore, active cooling at temperatures below ambient (at least 5-10 degrees) provides additional benefits that help solve the problems posed here.

[0017] As mentioned above, electroacoustic noise is caused by the interaction of audio signals with electric fields due to the natural propagation of heat in electronic component materials. Therefore, the electric field strength is lower when components are kept cool. Furthermore, the smaller the active area of ​​solid-state components, such as integrated circuits, the stronger the electric field. This therefore rules out the use of the latter type of components. This means that solid-state devices, with their large mass and size, such as those required for high-voltage and high-current operation, are less likely to generate electroacoustic noise. In addition to technical choices, capacitors also need to emphasize structural characteristics that help solve the same technical challenges posed here. Therefore, capacitors should be axial, meaning they have a cylindrical armature (which is inherently rigid) and use dielectrics with robust properties, making them particularly suited to the high-quality audio involved here. Polyester or polypropylene fibers meet these requirements.

[0018] Similarly, the active structure of the component (where the audio signal interacts with the thermal background phonon electromagnetic field) is made as mechanically rigid as possible. When valves are used, the electrodes and associated mechanical support and heat dissipation structures are made primarily of cylindrical layers of material and have as much mass as possible. When solid-state components are used, they should not be integrated circuits, and the mass of the active parts should be as large as possible, as they must meet the high-voltage and high-current operating conditions. Electroacoustic noise alters the harmonic content of an audio signal. This occurs not only by randomly suppressing some of the harmonic content, but also by altering the phase. This not only creates a sense of burned sound, but also reduces the fidelity of the stereo image. This invention offers significant advantages for driving multi-channel speakers. For this reason, negative feedback, which is commonly used in conventional audio equipment, is avoided because it alters the harmonic content of the original signal, including its phase. Negative feedback creates effects that become part of electroacoustic noise.

[0019] The symmetrical circuit topology is extended to the output stage using Circlotron circuits (see C.T. Hall, "Parallel Opposed Power Amplifiers," U.S. Patent No. 2,705,265 (1955), and Bongiorno, "Audio amplifier," U.S. Patent No. 4,229,706A (1980)). The Circlotron concept is a bridge configuration using a floating power supply and an active power supply with the same electrical conduction mode (i.e., electrons only), making it suitable for low electro-acoustic noise. While the Circlotron approach is also discussed in the Karsten and Berry patent, the invention described here uses specialized circuit components to reduce electroacoustic noise. Furthermore, i) neither local nor global negative feedback is used, and ii) the implementation of the solid-state output stage, while similar to the Buongiorno circuit, has the fundamental difference of operating in Class AB rather than Class A. The problem posed here is different from that of conventional Hi-Fi amplifiers, which have harmonic distortion levels far below the minimum audible level (around 1%). Instead, the present invention satisfies the following conditions: i) harmonic distortion is below the threshold of audibility, and ii) electroacoustic noise is dramatically reduced by the unique technology described here.

[0020] This invention demonstrates that electroacoustic noise can be reduced even with solid-state components, resistors, and capacitors kept at low temperatures. This requirement clearly does not apply to electronic vacuum tubes. However, cylindrical electrodes, in particular, are less susceptible to electroacoustic noise due to their large extension and mass. Therefore, electroacoustic noise can be reduced by using solutions that make the electrodes more resistant to electromechanical stress and therefore less susceptible to noise. More specifically, triode amplifiers for low-power applications (0.5 watts to 1 watt) typically use layers approximately 0.10 mm to 0.15 mm thick for the anode (and mechanical support and heat dissipation elements). As a result of the inventive step of this invention, electroacoustic noise is significantly reduced by using a thickness of 0.4 mm instead. The same criterion of using electrodes at least twice as thick applies to high-power vacuum tubes (50 watts), where the standard thickness of approximately 0.4 mm is increased to at least 0.8 mm. This is therefore a real option for developing new vacuum tubes truly designed specifically for high-quality audio applications.

[0021] To reduce electroacoustic noise, electron tubes are polarized at a relatively high anode current (close to the tube's center design value), which makes them more resistant to the development of electromechanical stresses. Therefore, using electrodes with a larger mass allows them to be operated at a lower anode current (which consequently saves energy from the power supply), which reduces the electroacoustic noise level compared to using standard vacuum tubes, which must be operated at a higher anode current to suppress noise.

[0022] For a given amplitude signal, even the lowest local electric field is favored by vacuum tubes (compared to solid-state devices) due to the large inter-electrode gap. The resulting reduction in local electric field strength actually has the beneficial effect of reducing the interaction of the acoustic signal's electromagnetic field with the phonon background electromagnetic field. In a further important departure from prior art, the present invention operates solely by connecting the output stage directly to the loudspeaker, without the use of a transformer or crossover network, a choice that also helps reduce electro-acoustic noise. This proves to be an additive phenomenon, in the sense that each technical choice contributes to noise reduction. If something is omitted, noise increases significantly, but because the appropriate technical choices remain, the sound quality improvement is not completely eliminated. This explains why certain examples of prior art amplifiers can provide slightly better sound quality than others. In reality, one or more of these choices may be included for coincidence, resulting in manufacturers mistakenly believing, based solely on experience, that they have discovered a recipe for valuable euphonic distortion that should be carefully preserved. Prior art technology inherently fails to return audio signals with harmonic integrity, adversely affecting voices and instruments. In fact, violins are rarely amplified because prior art electronics impair intonation. The same applies to double basses, which require amplification in jazz music, for example. The double bass generates richer harmonic content at lower frequencies than other instruments. Using this invention, the double bass gains significant benefits in timbre and sound quality.

[0023] Low electroacoustic noise makes it possible to restore audio signals while preserving the integrity of their harmonic content, including phase relationships, which is an essential condition for perfect reconstruction of the stereo sound image. Therefore, this invention can be realized in any high-quality audio equipment. The potential of digital audio can ultimately be effectively utilized by creating analog circuits that interface with the digital modules of any equipment (mixers, CD players, etc.). In fact, analog-to-digital and digital-to-analog interfaces typically require amplifier, buffer, and filter modules. Implementing these modules according to the requirements of this invention allows low electroacoustic noise in any digital audio equipment. It is known that music production studios use speakers with very expensive audio transducers made from special materials and driven actively or passively by amplifiers. As mentioned above, the weak spot lies in the amplifier, not the audio transducer. Therefore, with this invention, it is possible to obtain the best sound quality even with conventional, even inexpensive, transducers. By the same logic, even less expensive instruments, such as electric guitars, can be made to perform better than the finest instruments equipped with conventional electronics using this invention. [Brief explanation of the drawings]

[0024] [Figure 1] A block diagram of a typical conventional vacuum tube guitar amplifier. [Figure 2] A diagram of the input stage of a typical conventional tube guitar amplifier. [Figure 3] Wiring diagram showing a specific method of manufacturing a low electroacoustic noise musical instrument amplifier with an output stage that includes a floating bridge module that operates over the entire frequency range. [Figure 4] Detail of the circuitry included in the filter and isolation stage 40 and the filter and bias stage 400 shown in FIG. [Figure 5]Detail of the output stage of the amplifier in Figure 3, with two floating bridge modules operating in two different frequency bands. BEST MODE FOR CARRYING OUT THE INVENTION

[0025] Since the present invention uses only symmetrical differential amplifier circuit topologies, an unbalanced input signal, such as that from a guitar pickup, is converted to balanced by a long-tailed pair differential amplifier circuit including devices 11 and 12 and a corresponding constant current source 31, as shown in Figure 3. The required voltage amplification is obtained by cascading one or more differential amplifier stages, each including devices 11' and 12' and a corresponding constant current source 31'. Since the differential amplifier stage primarily requires resistors as passive components, the resistive elements are wirewound with a mechanically rigid structure and a circular cross section with the largest possible diameter. Negative feedback must be avoided, which causes voltage drops at high frequencies, especially in solid-state voltage amplifier stages. Therefore, the frequency response must be compensated by inserting the appropriate modules 40 and 400 shown in Figure 3. The former provides isolation and filtering functions, while the latter provides additional filtering and polarization of the output devices. The number of circuit elements is kept as low as possible to avoid increasing electroacoustic noise. The filter circuit is necessary to flatten the frequency response; a simple RC network with a divider function is sufficient to achieve this.

[0026] Module 400 also features a crossover function for actively driving speakers if required (see Figure 5). In the latter case, the filter network is of the well-known "unity gain, single feedback" type, and the required constant current sources (for the associated buffer circuits) are constructed using active devices rather than simple resistors. In summary, the buffer and crossover filter modules use only circuits that include common cathode, common emitter, and common source circuits in vacuum tube, junction transistor, and MOSFET implementations, respectively.

[0027] Active cooling of circuit components (not vacuum tubes) at room temperature reduces electroacoustic noise, therefore the invention should be implemented using only solid state active devices. Without active cooling, the best results with the lowest electroacoustic noise will be achieved by considering the active speaker drive options shown in Figure 5. Because the low frequency output stage is fully solid state, it is avoided to implement such an output stage with two or more pairs of vacuum tubes in parallel to more easily provide the required output power. For low frequencies, transistor implementations of the respective output stages are used, as is done in U.S. Patent 9306510B1 (2016) by Robling, entitled "Frequency-Dependent Dual Solid-State and Vacuum Tube Power Amplifier Section for Musical Instrument Amplifiers." The latter is suitable for bass guitars, which Robling patents often use actively driven two-way speakers. However, that patent addresses a different technical problem than the present application. Indeed, for example, Robling patents say nothing about the structural characteristics of circuit components or the appropriate circuit operating conditions that would help reduce electroacoustic noise.

[0028] Unlike the Robling patent, this invention is fully valid for electric guitars (as well as bass and other instruments) because it demonstrates, for the first time, that the tonal characteristics desired by guitarists do not necessarily require a full-band speaker, as was the case with the early guitar systems imitated in the prior art. The use of active speaker drive allows for uncompromising electroacoustic noise reduction. The speaker is connected to the amplifier without a filter network or transformer, and the vacuum tubes in the power output stage are biased at a relatively high current. Woofers operating at the lowest frequencies are best driven by solid-state output modules; the use of multiple parallel-connected power tubes in the output stage leads to excessive power consumption from the network and increased cost and size. Therefore, vacuum tube amplifier modules are used only for frequencies above 200 Hz to 300 Hz. The following topics highlight the substantial differences between the subject matter of this patent, which has a different technical challenge (producing lower measured distortion figures) than the present application (which is to suppress noise types detectable only by auditory comparison tests).

[0029] Rozemblit's U.S. Pat. No. 5,604,461A (1997) "Transformerless Output Vacuum Tube Audio Amplifier" shows an audio amplifier in which interstage coupling by capacitors is not required, but a similar type of coupling is compatible with solving the problem posed in this application. Furthermore, Rozemblit's patent shows a "long-tail pair" circuit using a simple resistor as a constant current source, whereas in this application, such a constant current source includes an active element. The latter possibility is shown, for example, in Takehara's U.S. Pat. No. 4,241,313 (1980) "Audio Power Amplifier," but neither patent provides any suggestion regarding the structural characteristics of the circuit components. In King's patent WO 87 / 07554 (1987) "Sound Reproduction System," an amplifier is connected to the speaker through a passive crossover filter network containing resistors, capacitors, and even inductors. The resistors are wire-type to provide the power required for the passive crossover. However, no special construction characteristics are required except to meet quality standards for the particular application. Similar requirements are made for the type of capacitors used in the filter network. In contrast, in the present application, as mentioned above, the loudspeakers are always connected directly to the amplifier, and if multi-way driving of the loudspeakers is required, this is achieved in an active way, i.e., by filter stages included in the amplifier and constructed using the same criteria as those for electroacoustic noise suppression discussed herein. A further important feature of the invention described here is the specification of parameters (mass and shape) related to the structural properties of the passive and active components used in the circuit.

[0030] FIG. 3 shows a schematic example of an audio amplifier particularly suited to guitars, which has properties that minimize electro-acoustic noise in a configuration capable of driving any type of speaker. In this embodiment, the voltage amplification stage is implemented using vacuum tubes, while the output stage is constructed using solid-state technology. Active cooling of this final stage device by at least 10°C further reduces electroacoustic noise. Extending the cooling to other devices allows the entire circuit to be implemented in solid-state, significantly reducing the types of noise present within the device. If the input signal is unbalanced (as is common with guitars), it is applied to the amplifier's gain potentiometer (1). To significantly reduce electroacoustic noise, the potentiometer used in this invention consists of at least 12-position switches, with one or two banks depending on whether a single-ended or balanced signal is being processed. As mentioned above, polarized wirewound resistors are mounted on the switches to function as potentiometers.

[0031] The differential voltage amplifier circuit (vacuum tubes 11, 12 and a current source including device 31) generates a balanced signal, which (together with other technical options described here) is a prerequisite for obtaining low electro-acoustic noise. The diagram shows the optional cascading of further voltage amplifier stages (vacuum tubes 11', 12' and a current source including device 31') to obtain the desired gain. This stage is amplified AC. This is coupled to the next buffer stage (40), which includes devices (13) with their own constant current sources of the type shown in FIG. 4, i.e., active constant current source devices (33). To obtain low electro-acoustic noise, it is important to use the same type of buffer circuitry as in Figure 4 for the buffering and equalizing functions of stage 40, and also for the polarization function of stage 400 (see Figure 3), which ultimately provides the crossover function for a two-way amplifier embodiment (Figure 5) or if more ways are required.

[0032] In particular, to achieve the required response accuracy of the crossover filters used to actively drive speakers (see Figure 5), the filter module uses the "Unity Gain, Single Feedback Implementation" technique (see "Introduction to Modern Network Theory," McGraw-Hill Education, 2014). This is because only buffer stages are used, rather than arithmetic circuits with appropriate voltage gain. These buffer stages use discrete active elements, as shown in Figure 4. This choice eliminates the need for amplifier stages, which must be differential, resulting in a complex circuit with many components and increased noise in the object. For example, if active cooling of the circuit components is not required, a solution (see Figure 5) is required to drive the speaker in at least two ways. In this case, as mentioned above, the crossover frequency should be around 200 Hz to 300 Hz. This is to avoid using multiple pairs of vacuum tubes in the output stage 60 designed to operate above that frequency. This choice is particularly effective for instruments that generate harmonics at very low frequencies, such as double bass, bass guitar, and certain wind instruments that often require amplification in jazz music.

[0033] In an embodiment of the invention as a guitar amplifier, module 400 with crossover filter functionality (only required when operating with multiple output modules as in FIG. 5) is equipped with a dual potentiometer volume (master) and an additional dual potentiometer for adjusting the level of the low frequencies (bass tones). These potentiometers are fabricated as described above. When using a circuit in conjunction with a distortion module, this is inserted by separating the connections between states 40 and 400 and should be considered with the same criteria as those for electroacoustic noise reduction discussed here. For musicians, the use of distortion devices is an essential option for creating effects, such as with the aforementioned electric guitar. In guitar amplifiers, distortion functionality is typically achieved by activating a distortion device connected to the amplifier via an external loop (FX loop) or by activating a distortion module embedded in the amplifier itself, as in the case of the prior art in Figures 1 and 2. 1, 2. The method of artificially altering the signal coming from the instrument's pickups is based on the concept of waveform squaring, which is achieved by operating it under powerful amplification. The result is a sinusoidal signal that becomes trapezoidal in the stronger signal sections, becoming increasingly angular as the signal amplitude increases. This corresponds to the addition of artificial harmonics unrelated to the audio signal. The result is overdrive modes with progressively higher levels of distortion, from crunch to lead to "fuzz".

[0034] In addition to waveform sharpening, guitarists may choose to modify their sound in other ways, such as tremolo, achieved with the appropriate oscillator circuit. A more commonly used option is reverb, originally developed by Hammond and later licensed by instrument manufacturers such as Fender. Reverb is achieved by feeding the instrument's signal into the amplifier's input. The signal is pre-amplified and split into two paths: one path is the "dry" signal, without any modification, and the other is connected to a buffer stage and sent to the input of a device consisting of one or more springs. The ends of the springs are connected to two electro-acoustic transducers, which form the input and output of the reverb device. The signal coming out of the device's output is "wet," due to the resonance caused by the springs, and is then mixed with the "dry" signal.

[0035] As mentioned above, the buffer stage 40 of the amplifier chain can drive other types of distortion tools, such as a waveform shaping device or a spring unit for reverb mode. Even with the latter type of sound, the low electroacoustic noise and associated excellent sonic performance characteristic of this invention are achieved. This is true when the same types of circuitry and component criteria are used as described above. The circuits required for amplification, buffering, and wet / dry signal balancing must use the following: i) the same type of balanced signal circuitry, ii) a differential amplifier stage, iii) buffer circuits suitable for balanced signals, iv) no negative feedback, and primarily appropriate types of passive and active components. The circuit in Figure 5 can be easily extrapolated to easily build low electroacoustic noise systems with two or more active modes, and is particularly useful for driving speakers in music production studios in active mode. Because the speakers are driven in phase, overlap between the frequencies processed by each type of speaker is minimized and the overall phase response is optimized.

[0036] The high-frequency output stage module(s) (see Figure 5) use the original Circlotron vacuum tube configuration. The low-frequency modules are implemented with transistors, but differ from Bongiorno's modules in that they are i) polarized in class AB and ii) feature a standard voltage amplifier circuit different from that used by Bongiorno. Bipolar junction transistors are explicitly used for the solid-state output stage (51) because they offer the advantages of lower cost compared to MOSFETs, their ability to withstand relatively high collector currents, and, above all, lower crossover distortion under load. Circlotrons operate in class AB, but this operation is not required. On the other hand, the output transistor driver stage is implemented with MOSFETs, which offers the advantage of lower loading on the corresponding voltage amplifier stage, even if it is implemented with vacuum tubes as in Figure 3. To compensate for the natural frequency drop in such amplifier circuits without negative feedback, the degree of frequency equalization performed in module 40 (and module 400) is generally less pronounced in the case of vacuum tubes and more pronounced in the case of solid-state implementations of the voltage amplifier stage. In this regard, simple RC cells with resistive dividers are used, which in both cases are made from components with the structural characteristics described above.

[0037] The bias current for the output tubes is obtained by appropriate selection of the resistor dividers contained in the filter and bias module (400) to obtain a sufficiently high bias current (e.g., on the order of several hundred milliamps for audio frequency output triodes). This relatively high current is necessary, as mentioned above, to give the tube electrode system (and associated support and heat dissipation components) a high resistance to stresses occurring on a microscopic scale. For the same reason, the tubes that may be used in the driver, filter, and isolation stages are also polarized at currents slightly lower than the normal maximum expected for these tubes.

[0038] The output power transistors 51, 52 are also biased by selecting an appropriate resistor divider included in the module 400. Thermal stabilization of the output power transistors is achieved by a simple diode array placed at the thermal contact of the transistor case and a voltage multiplier function circuit. A high DC voltage source (approximately 80 V) is selected to power the output transistors, with a relatively low bias current (approximately 30 mA). Both choices are suitable for low electro-acoustic noise. As a general consideration, in addition to the power supply electrolytic filter, at least one capacitor with the above characteristics connected close to the amplifier circuit will ensure low electroacoustic noise at the output. Finally, base / gate resistors (around 100 Ω) of the stabilizing transistors are essential. In vacuum tube implementations, replacing these resistors with short circuits can sometimes achieve low electroacoustic noise.

Claims

1. A musical instrument amplifier implemented using electron tubes or solid state components and having low electro-acoustic noise, comprising: a) an input stage comprising at least first and second input terminal means (10, 20) suitable for receiving at least an input signal; b) a preamplifier stage including at least a portion having a long tail pair circuit and a ground terminal (Gr); c) a buffer and filter stage (40) including at least first and second input terminals (41, 42) and at least first and second output terminals (43, 44); d) a filter and bias stage (400) including at least first and second input terminals (401, 402) and at least first, second, third and fourth output terminals (403, 404, 405, 406); e) an output stage including at least a floating bridge module (50) operating in at least a first frequency range and including at least first and second DC power supplies (511, 512); f) at least first and second output terminal means (A10, A20) for connecting one or more speakers operating in said first frequency range; said electron tube comprising at least a first part called the anode, at least a second part used as a mechanical support for the anode, and at least a third part used for heat dissipation of the anode; The portion of the preamplification stage having a long tail pair circuit comprises: i) first and second preamplifier devices (11, 12) each having first and second input terminals (A, B), first and second terminals (C, D), and first and second output terminals (E, F); ii) a constant current source comprising a constant current source device (31) having a power terminal (G), a control terminal (H), and an output terminal (I); the first and second input terminals (A, B) of the first and second preamplifier devices (11, 12) are connected to the same first DC voltage source (21) referenced to the ground terminal (Gr); The control terminal (C) of the first preamplifier (11) is connected to the input terminal means (10); the first and second output terminals (E, F) of the first and second preamplifier devices (11, 12) are connected to each other and to the output terminal (I) of the constant current source device (31) of the constant current source of the first part of the preamplifier stage; The power supply terminal (G) of the constant current source device (31) is connected by a connection means (Ga) to a second DC voltage source (22) that is referenced to the ground terminal (Gr), The control terminal (H) of the constant current source device (31) of the constant current source is connected to the second DC voltage source (22) by a connection means (Ha). the buffer and filter stage (40) comprises at least a buffer device (13) and a constant current source including at least a constant current source device (33); The buffer device (13) has an input terminal (L), a power supply terminal (N), and an output terminal (P), The constant current source device (33) has a power supply terminal (R), a control terminal (T), and an output terminal; The power supply terminal (N) of the buffer device (13) is connected to a third DC voltage source (23) referenced to a ground terminal (Gr); the output terminal (P) of the buffer device (13) is connected by a connection means to the output terminal of the constant current source device (33) of the constant current source of the buffer and filter stage (40); The power supply terminal (R) of the constant current source device (33) is connected to the second DC voltage source (22) by a connecting means (Ra), The control terminal (T) of the first constant current source device (33) is connected to the second DC voltage source (22) by a connecting means (Ta); The first and second output terminals (43, 44) of said buffer and filter stage (40) are connected respectively to first and second input terminals (401, 402) of a filter and polarisation stage (400). The first floating bridge output module (50) comprises at least first and second output devices (51, 52), each having first and second input terminals (A1, A2), first and second power supply terminals (B1, B2), first and second output terminals (C1, C2), and first and second DC power supplies (511, 512); the first and second input terminals (A1, A2) of the first and second output devices (51, 52) of the output module (50) are connected by connecting means to the first and second output terminals (404, 403) of said filter and polarization stage (400), respectively; the first DC power supply (511) is connected between a power supply terminal (B1) of the first output device (51) of the first output module (50) and an output terminal (C2) of the second output device (52) of the first output module (50); the second DC power supply (512) is connected between a power supply terminal (B2) of the second output device (52) of the first output module (50) and an output terminal (C1) of the first output device output (51) of the first output module (50); The first and second output terminal means (A10, A20) are connected to a load between the first and second output terminals (C1, C2) of the first and second output devices (51, 52) of the first output module (50), respectively. At least one portion of the amplifier comprises at least a potentiometer, a capacitor, or a resistor; The resistor is of the wirewound type having a circular cross section of at least 15 / 1000 mm or greater for at least the majority of its length.

2. 10. The amplifier of claim 1, wherein the resistor has a winding direction.

3. 10. The amplifier of claim 1, wherein the potentiometer is constructed using wirewound resistors having a cross section of 0.015 millimeters or greater.

4. 10. The amplifier of claim 1, wherein the capacitor has an axial shape and is of the polyester or polypropylene type with an operating voltage greater than 500 volts.

5. 2. The amplifier of claim 1, wherein the output stage comprises at least a second floating bridge output module (60) operating in at least a second frequency range above the first frequency range. the second floating bridge output module (60) comprising third (611) and fourth (612) DC power supplies and third and fourth amplifier output terminal means (A20, A21) for connecting one or more speakers to be driven in the second frequency range; the second floating bridge output module (60) comprises first and second output devices (61, 62) each having first and second input terminals (D1, D2), first and second power supply terminals (E1, E2), and first and second output terminals (F1, F2); the input terminals (D1, D2) of the first and second output devices (61, 62) of the second floating bridge output module (60) are connected by connecting means to third and fourth output terminals (406, 405) of the filter and polarization stage (400), respectively; the third DC power supply (611) is connected between a power supply terminal (E1) of the first output device (61) of the second floating bridge output module (60) and an output terminal (F2) of the second output device (62) of the second floating bridge output module (60); the fourth DC power supply (612) is connected between a power supply terminal (E2) of the second output device (62) of the second floating bridge output module (60) and an output terminal (F1) of the first output device (61) of the second floating bridge output module (60); The output terminals (F1, F2) of the first and second output devices (61, 62) of the second floating bridge output module (60) are connected to third and fourth output terminal means (A20, A21) of the amplifier, respectively.

6. 10. The amplifier of claim 1, wherein at least one of the first, second, and third portions of the electron tube has a curved shape over at least one-third of a surface area of ​​the portion.

7. 10. The amplifier of claim 1, wherein the thickness of the material of at least one of the first, second, and third portions of the electron tube exceeds 0.1 millimeters.

8. 10. The amplifier of claim 1, wherein at least one of said electron tubes is biased with a current equal to at least two-thirds of the maximum center design value of said electron tube.

9. 10. The amplifier of claim 1, wherein at least one of the output devices of the output module of the output stage is implemented with solid state components and biased with a current not exceeding 50 milliamps.

10. 10. The amplifier of claim 1, including a heat pump device comprising a module having a first portion that absorbs heat and a second portion that releases heat into a room, the first and second power terminals connected to a power source; Here, the housing of at least one device and component other than an electron tube included in at least one portion of the amplifier is maintained at a temperature at least 5°C below room temperature by being in direct or indirect contact with a first portion of the heat pump device that absorbs heat.

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