Musical instrument amplifier

Abstract

Implementations and methods of an audio amplifier having a special function of driving a speaker without generating electro-acoustic noise are described herein. The phenomenon is inherent in an analog circuit, and is caused by the propagation of sound and heat when an audio signal acts on a circuit element material. The structure which is more resistant to electromechanical stress is not easy to generate such noise, and the appropriate circuit can also eliminate the residual effect. Compared with the prior art, the tone quality is greatly improved, and a music player has a greater degree of freedom in the aspect of tone research and can play music more easily. Similar improvements are also obtained when the invention is used for driving loudspeakers of music making studios and all applications requiring optimal sound quality.

Description

Technical Field

[0001] Embodiments of this specification relate to the concepts of audio amplifiers and preamplifiers, including devices particularly suitable for electric guitars, musical instruments in general, and for driving studio speakers for music or concert production, including any electronic application where uncompromising sound quality standards are required. Background Art

[0002] Experts in audio amplifier technology generally believe that in order to make the signal from an instrument's pickup or microphone sound pleasing to the ear, a certain degree of distortion is necessary to achieve a more pleasing sound. In fact, the sound of high-fidelity amplifiers (i.e., amplifiers with very low distortion as measured by instruments) is often considered unsuitable for musical instruments because the timbre and overtones are too cold, appearing "burnt." Consequently, guitarists have continued to favor transistor amplifiers, even after more reliable, hum-free amplifiers attempted to replace older tube amplifiers (see: R.O. Ham, "Tubes and Transistors," 43rd Audio Engineering Society Convention, New York, September 14, 1972). According to the latter reference, subjective psychological factors can cause listeners to judge the sound of overly perfect solid-state equipment as unpleasant and unnatural, precisely because tube distortion is perceived as too low. Therefore, according to experts, there is no objective technical problem to be solved in audio amplifiers, as early equipment suitable for movie theaters and electric guitars simply possessed the supposedly beneficial effect of producing the necessary pleasing distortion for random reasons.

[0003] As a result, patents focusing on simulating the characteristics of vacuum tubes have continued to emerge over the decades, such as: "Guitar amplifier", US Patent No. 20130136278A1, Quilter (2013); "Vacuum tube amplifier", US20150170627A1, Hummel (2015); "Method and apparatus for audio signal distortion and vacuum tube amplifier simulation", N. Gallo, US Patent No. 20080218259A1 (2008); "Guitar amplifier", US Patent No. 20130136278A1, Quilter (2013); "Vacuum tube amplifier", US20150170627A1, Hummel (2015); "Semiconductor amplifier with characteristics of vacuum tube amplifier", US Patent No. 20140170627A1. Eric K. Pritchard (1987), U.S. Patent No. 4,809,336A, "Solid-State Audio Amplifier Simulating a Vacuum Tube Audio Amplifier," Bruce Keir, U.S. Patent No. 5,467,400A, e pure, "Solid-State Circuit Simulating Vacuum Tube Compression Effects," U.S. Patent No. 5,524,055A; Jack C. Sondermeyer, "Solid-State Simulation of Vacuum Tube Audio Power Amplifier," E.K. Pritchard (1994), U.S. Patent No. 5,636,284A, Douglas R. Frey (1982), "Adjustable Distortion Guitar Amplifier," U.S. Patent No. 4,495,640A.

[0004] A similar problem exists in the realm of so-called high-end audio amplifiers. Unlike high-fidelity amplifiers, which have measured distortion rates of virtually zero, high-end audio amplifiers are designed based on empirical recipes designed to mimic the measured harmonic distortion patterns found in amplifiers that the public considers to be optimal for listening. See, for example, Karsten's "Amplifier and Preamplifier Circuits," published in 2001 (U.S. Patent No. 6,242,977 B1) and Berry's "High-Fidelity Floating Bridge Amplifier," published in 2002 (U.S. Patent No. 6,747,513 B1).

[0005] In summary, prior art generally assumes that audio amplifiers, in order to improve sound quality, perform certain changes to the input signal, shrouding the sound in a supposedly euphonious veil. According to prior art, the source of this beneficial distortion lies in the characteristics of vacuum tubes. Although solid-state devices are increasingly believed to be able to fully emulate these characteristics, guitarists still prefer amplifiers based on early vacuum tube circuits. This prior art approach overlooks important factors that cannot be measured using currently available instrumentation. Therefore, the prior art assumption that subjective psychological factors, rather than technical / objective factors, determine the sound quality of an amplifier is merely speculation, unproven.

[0006] The explanation we offer here, contrary to the explanations left unaddressed by the prior art, is as follows: i) Vacuum tubes, along with the appropriate types of electronic components and circuits, create a relatively weak source of electroacoustic (or antiharmonic) noise, a phenomenon described later, the existence of which was overlooked by the prior art; ii) Therefore, to improve sound quality, the goal is not to add any supposedly pleasant distortion to the audio signal, but rather to eliminate all types of distortion and noise, including those described above. Consequently, the sound quality problem of audio amplifiers is far from being solved by the prior art.

[0007] To understand the innovations described here, we will consider the typical circuit diagram of Figure 1, which relates to a well-known guitar amplifier from the prior art, essentially replicating a tube amplifier from over half a century ago.

[0008] Guitar amplifiers often require a distortion device that modifies the pickup's sound appropriately to suit the musician's expressive and artistic needs. This modification is achieved by square-wave processing, introducing a reverb effect obtained by appropriate spring devices, or other methods that artificially add harmonic components to the instrument's signal.

[0009] Regardless of whether the sound is natural or artificially distorted, electroacoustic noise significantly alters the harmonic patterns that give any sound its individual character. However, musicians cannot control or eliminate this noise, as it becomes part of the sound through any existing technological equipment. Consequently, the sound is stripped of its individuality and originality, and reproduced with a noticeable degree of standardization. This is the true effect of electroacoustic noise, which deprives musicians of the creative freedom they seek to create sound based on the harmonic richness of their music.

[0010] Because this invention eliminates electroacoustic noise, musicians can finally enjoy the true harmonic fullness of sound, freeing themselves to fulfill their artistic and expressive needs.

[0011] In Figure 1, the signal from the instrument pickup is configured in a single path (unbalanced) from the input to the output stage, see blocks U5a and U5b. The output stage is also shown, including the push-pull devices that power the output transformer.

[0012] The figure shows the circuit components used to adjust the gain and volume (maaastrer), as well as the circuit components of the tone controller for different channels to produce different sound modes (clean tone or distorted tone).

[0013] Another technical solution commonly used in the prior art is to use a semiconductor switch in the signal path of the amplifier module including the device U2a, see Figure 2 Furthermore, electronic circuits typically use metal film, carbon composite, or plastic film resistors and potentiometers, which have the desirable characteristic of low electromagnetic noise pickup by the power supply. Furthermore, there are often no specific specifications regarding the structural characteristics of capacitors and active devices (electron tubes). Prior art manufacturers claim to offer special designs (possibly handcrafted) and to use specialized components, but these manufacturers typically do not explain the rationale for these choices, which appear to be made for purely commercial reasons. These choices align with the deeply held belief among experts in the field of guitar amplifier technology that achieving the sound quality desired by musicians requires satisfying certain recommended requirements, rather than addressing any technical flaws that ultimately affect the circuit.

[0014] Another important aspect is how to drive speakers, as conventional audio requires full-range capability. Therefore, conventional tube guitar amplifiers are equipped with output transformers that drive one or more speakers through the same pair of output terminals. Only with bass guitars (often simply referred to as "bass") do two-way speakers—those with at least one dedicated low-frequency speaker and at least one dedicated high-frequency speaker—are they used. The crossover frequency is approximately 2 kHz, typically achieved using a passive crossover network. Summary of the Invention

[0015] Unlike the prior art, the present invention is based on the following concept: an electronic circuit truly designed for optimal sound reproduction does not add any kind of artifacts to the audio signal, including those that, according to the prior art, create so-called euphony effects, as well as any actual physical changes that are ignored by the prior art because they cannot be captured by instrumental measurements. However, such measurements are insensitive to the extremely rich and complex harmonic content of even the most insignificant audio signals.

[0016] Therefore, comparative listening tests were conducted between standard equipment and a prototype designed to implement the present invention. The results reported here reveal the objective reasons for the true differences in audio amplifier sound quality. The test input signals were generated directly by instrument pickups or microphones, rather than recorded music (albeit high-quality recordings). In fact, the latter are always subject to electroacoustic noise due to the electronic chain used for recording.

[0017] Instruments that require amplifiers, such as guitars, are often played with distortion devices. Musicians often want to alter the signal emitted by their instruments, sometimes significantly, to the point of almost completely deviating from the original sound. However, these intentional modifications must remain within the musician's control. Antiharmonic noise is inherent in existing electronic devices and is an artifact that the musician cannot control in any way. Therefore, musicians have a significant advantage in inventiveness because any artificial changes to the original sound are completely under their control, unlike with any existing device.

[0018] This means that musicians should not be subject to the sonic standardization imposed by any electronic device. Consequently, they will not tolerate any modifications, even if those modifications are intended solely to improve listening quality, as the prior art claims to do with its high-end audio electronics. The resulting homogeneity actually conflicts with the fundamental requirement for musicians to exercise freedom of expression. No prior art device can respect this freedom, as it is invariably affected by electroacoustic noise. To counteract the discomfort caused by this noise, manufacturers (ignoring its existence) often mask the sound with so-called pleasant distortion.

[0019] Now, the present invention solves this problem by meeting the real needs of musicians with a new sound standard that is not affected by: i) any instrumental measured distortion; and ii) noise that was not foreseen by the prior art but that can be easily detected by the human ear by comparing the present invention with similar prior art devices.

[0020] Electroacoustic noise, or antiharmonic noise, is a new physics concept discovered by this invention. This noise is inherent to circuit components and is the result of microscopic electromechanical stresses in the materials that make up the components when an audio signal passes through them. Even a trivial audio signal is composed of numerous harmonic elements that give the sound its characteristic properties. This noise results from the interaction between the signal's harmonic elements and the natural propagation of sound and heat in the circuit component materials (phonons).

[0021] Using a circuit topology with a high common-mode rejection ratio is the first requirement for suppressing electroacoustic noise.

[0022] Therefore, it is beneficial to consider only differential circuit topologies. In addition, it is also desirable to connect the amplifier directly to the speaker without the intervening passive crossover network. The following references discuss similar issues.

[0023] Rozemblit, in US Pat. No. 5,604,461 (1997), discloses an audio power amplifier connected to a long-tailed pair circuit preamplifier and an output buffer / bias stage that provides output terminals connected to a speaker. Quilter, in US Pat. No. 2013 / 132678A1, presents a guitar amplifier that incorporates a solid-state module designed to simulate the overload distortion (via clipping and power droop) of a vacuum tube amplifier stage and is equipped with buffering, equalization, and gain control. Robling, in US Pat. No. 9,306,510 B1, presents a dual solid-state and vacuum tube amplifier incorporating a two-way crossover designed for direct connection to a loudspeaker. Malcolm, in "Floating Bridge Amplifier Configuration Incorporating Floating Supply Error Feedback Location" (AES, 60 East 42nd Street, Suite 2520, New York, NY 10165-2520, USA), demonstrates how a floating bridge setup can be used to improve audio amplifier design. Berry in US 7.187.233 B1 (2007) shows a floating bridge amplifier including a long tail pair amplifier stage.

[0024] Further examples of related patents include: US Patent 4,272,728A, “Differential Input Amplifier Circuit,” by HA Wittlinger; US Patent 2010 / 001797A1, “Differential Amplifier,” by K. Ishiguro and Y. Takahashi; and US Patent 2008 / 008335A1, “Amplifying Audio Signals,” by DJ Mate.

[0025] For those skilled in the art, the technological choice for solving the problem presented here is counterintuitive. That is, even with minimal power consumption, all resistors (including those not in the signal path) are wirewound. These components lack any supports to increase heat dissipation. In fact, increasing the cross-section of the resistor elements is crucial for reducing electroacoustic noise. Eliminating the additional structures and materials used to increase heat dissipation contributes to size reduction, weight reduction, and cost reduction. Thin-film resistor elements are more susceptible to electroacoustic noise generation. A circular cross-section offers greater inherent mechanical rigidity, making the overall structure less susceptible to electroacoustic noise generation.

[0026] Wirewound resistors are known to be very sensitive to electromagnetic noise from the power supply. This problem can be addressed by using polarized wirewound resistors (i.e., resistors with a specific winding direction). By connecting one or more pairs of resistors in series, polarized in opposite directions, and placing them side by side, a specific resistance value can be achieved. The resulting component is non-inductive and inexpensive to manufacture. In this case, the cross-section of the resistor element can be even larger than using a single element with double the resistance value, resulting in lower electroacoustic noise. In fact, larger resistor elements have a lower noise generation potential because their greater mass also provides greater immunity to electromechanical effects. The greater the thickness of the resistor element, the more sensitive the noise suppression effect. Thicknesses greater than one ten-thousandth of a millimeter are acceptable, with a thickness of 30 ten-thousandths of a millimeter or greater being optimal.

[0027] Furthermore, contrary to the common belief that electroacoustic noise exists only along the audio signal path, due to the diffusion properties of sound and the propagation of heat through circuit component materials, electroacoustic noise actually spreads throughout the entire circuit, even reaching parts outside the signal path, such as power supply circuits and constant current source circuits. Using capacitors with appropriate structural characteristics (see below) can prevent noise from spreading to the amplifier output.

[0028] The output stage requires solid-state amplifiers rather than Class A amplifiers, which is counterintuitive given that Class A amplifiers are commonly used in the HiFi audio field (see, for example, Bongiorno, "Audio Amplifier," U.S. Patent No. 4,229,706A (1980)). To reduce electroacoustic noise, the solid-state output devices should be biased in Class AB and operated at relatively low currents to avoid over-enhancing the output device performance. Actively cooling them to at least ten degrees below ambient temperature provides additional benefits, helping to address the issues raised here.

[0029] As mentioned above, electroacoustic noise depends on the interaction of audio signals with electric fields, which are related to the natural propagation of heat within electronic component materials. Therefore, electric field strength is lower when component temperatures are lower. Furthermore, electric field strength is higher when the active area of a solid-state component is smaller, such as in integrated circuits. Therefore, these latter types of components are excluded. In short, solid-state devices with larger mass and size (such as those that operate at high voltages and currents) are less prone to electroacoustic noise.

[0030] Besides the choice of technology, capacitors should also take into account structural characteristics that contribute to solving the same technical problems presented here. Therefore, they should be of the axial type, i.e., with an armature of cylindrical geometry (intrinsically more robust), and use a dielectric with robust properties, therefore practically dedicated to the high-quality audio quality relevant here; polyester or polypropylene fibers can meet these requirements.

[0031] Similarly, the component's active structure (where the audio signal and the thermal background phonon electromagnetic field interact) should also be as mechanically rigid as possible. In the case of electron tubes, the electrodes and associated mechanical support and heat dissipation components should be as massive as possible and primarily constructed from cylindrical layers of material. In the case of solid-state components, these must not be integrated circuits, and their active parts must be as massive as possible, similar to the high voltage and current requirements they must operate under.

[0032] Electroacoustic noise alters the harmonic content of an audio signal, not only randomly suppressing some harmonics but also shifting their phase. This effect not only creates a sense of sound distortion but also impairs stereo image reconstruction. The present invention offers significant advantages for driving multi-channel speakers. This avoids the negative feedback commonly used in prior art audio equipment, which alters the harmonic content of the original signal, including its phase. The effects of negative feedback also constitute a component of electroacoustic noise.

[0033] Symmetrical circuit topology can be extended to the output stage using the Circlotron circuit (see: CT Hall, U.S. Patent 2,705,265 (1955) and Bongiorno, U.S. Patent 4,229,706A (1980)). The Circlotron concept is a bridge configuration that uses a floating power supply and active power devices with the same conduction mode (i.e., electrons only), which helps reduce electroacoustic noise.

[0034] The Karsten and Berry patent also considered the Circlotron approach, but the invention described herein uses a special type of circuit element to reduce electroacoustic noise. Furthermore: i) no local or global negative feedback is used, and ii) the solid-state output stage implementation, while similar to the Bongiorno circuit, fundamentally differs in that it operates in Class AB rather than Class A.

[0035] The problem posed here is quite different from that of prior art high-fidelity amplifiers, which have harmonic distortion rates well below the lowest value detectable by hearing (approximately one percent). In contrast, the present invention satisfies the following conditions: i) harmonic distortion is below the audible threshold; and ii) electroacoustic noise is significantly reduced thanks to the original technology described herein.

[0036] The present invention demonstrates that even solid-state components, resistors, and capacitors stored at relatively low temperatures can reduce electroacoustic noise. However, this requirement obviously does not apply to electronic vacuum tubes. These are less susceptible to electroacoustic noise due to the greater extension and mass of the electrodes, especially cylindrical electrodes.

[0037] Lower electroacoustic noise is thus achieved by using solutions that make the electrodes more resilient to electromechanical stresses and therefore less susceptible to noise generation. More specifically, amplifier triodes for low-power applications (0.5-1 watt) typically use a layer with a thickness of approximately 0.10-0.15 mm for the anode (as well as components for mechanical support and heat dissipation). Thanks to the inventive step, a thickness of 0.4 mm was used instead, significantly reducing electroacoustic noise. The same standard of using electrodes at least twice as thick also applies to higher-power tubes (50 watts), where the standard thickness increases from approximately 0.4 mm to at least 0.8 mm. This is therefore a genuine option for conceiving new electron tubes specifically for high-quality audio applications.

[0038] To reduce electroacoustic noise, the tubes are polarized with a relatively high anode current (close to the tube's center design value). This improves resistance to electromechanical stress. Consequently, using a higher-mass electrode allows operation at a lower anode current (thus saving power), which translates to lower electroacoustic noise levels than with standard tubes, which require higher anode currents to suppress noise.

[0039] Because of the large electrode gap, tubes can achieve their advantages (compared to solid-state components) even when the local electric field strength is minimal for a given signal amplitude. The resulting lower local electric field strength actually helps reduce the interaction between the electromagnetic field of the audio signal and the background field of phonons.

[0040] Another important difference from the prior art embodiments is that the present invention works by connecting the power output stage directly to the loudspeaker, without the need for a transformer or crossover network. In addition, this choice helps to reduce electroacoustic noise.

[0041] It turns out that this is an additive phenomenon: every technical choice contributes to noise reduction. If certain technical choices are omitted, the noise level increases significantly, but the improvement in sound quality is never completely eliminated, as other suitable technical choices are still present. This explains why one example of a state-of-the-art amplifier can sound slightly better than another: in fact, it may contain one or more of these choices simply by chance, so the manufacturer may mistakenly believe that they have found a precious recipe for pleasant distortion and are carefully preserving it simply for empirical reasons.

[0042] Existing technologies are inherently incapable of fully restoring the harmonic content of audio signals, adversely affecting the sound quality of vocals and musical instruments. Indeed, violins are rarely accurately amplified due to the degradation of pitch by existing electronic devices. The same is true for double basses, which sometimes require amplification, such as in jazz. Of all instruments, the double bass is the most capable of producing harmonic content, starting at the lowest frequencies and enriched in harmonics compared to other instruments. This instrument, when used in conjunction with the present invention, offers significant advantages in timbre and sound characteristics.

[0043] Due to the low electroacoustic noise, the harmonic components of the audio signal can be fully restored, including their phase relationships, which is essential for perfectly recreating the stereo image. Therefore, any high-quality audio device can be realized with this invention. The potential of digital audio can ultimately be effectively utilized by creating analog circuits that must interface with the digital modules of any device (mixer, CD player, etc.). In fact, analog-to-digital and digital-to-analog interfaces typically require amplifier, buffer, and filter modules. If implemented according to the requirements of this invention, these modules can provide low electroacoustic noise for any digital audio device.

[0044] It's no secret that music production studios often use loudspeakers equipped with very expensive audio transducers, even those made of exotic materials and driven actively or passively by amplifiers. As mentioned above, the weak point lies in the amplifier, not the audio transducer. Therefore, the present invention makes it possible to achieve top-quality sound even with conventional, even inexpensive, transducers.

[0045] Likewise, even a relatively inexpensive musical instrument, such as an electric guitar, can outperform the most sophisticated instruments equipped with prior art electronics by using the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1. Block diagram of a typical prior art tube guitar amplifier.

[0047] Figure 2. Schematic diagram of the input stage of a typical prior art guitar tube amplifier.

[0048] Figure 3. A special wiring diagram for an amplifier for low-noise musical instruments, with an output stage equipped with a floating bridge module operating over the full frequency band.

[0049] Figure 4. Circuit details of the filtering and separation stage 40 and the filtering and biasing stage 400 shown in Figure 3.

[0050] Figure 5. Detail of the output stage of the amplifier in Figure 3, equipped with two floating-bridge modules operating in two different frequency bands. Best Practice

[0051] Since the present invention only uses a symmetrical circuit topology of a differential amplifier, an unbalanced input signal (such as a signal from a guitar pickup) can be converted into a balanced form by a long-tailed pair differential amplifier circuit. The circuit includes devices 11, 12 and a corresponding constant current source 31, see Figure 3 The required voltage amplification factor is achieved by cascading one or more cascaded differential amplifier stages, for example, the amplifier cascade comprising devices 11 ′, 12 ′ and a corresponding constant current source 31 ′.

[0052] Since the differential amplifier stage requires mainly resistors as passive components, the resistive elements have a mechanically rigid structure and are of the wirewound type with a circular cross-section of the largest possible diameter.

[0053] Because negative feedback must be avoided, voltage amplifier stages (especially when using solid-state amplifiers) experience voltage drops at high frequencies and must be replaced by inserting Figure 3 Suitable modules 40 and 400 are shown to compensate for the frequency response. The former provides isolation and filtering, while the latter further filters and polarizes the output device. To avoid increasing electroacoustic noise, the number of circuit components should be kept to a minimum. A filtering circuit is required to flatten the frequency response; a simple RC network with a partition is sufficient for this purpose.

[0054] Module 400 can also perform a crossover function, if desired, for actively driving a loudspeaker (see Figure 5). In this latter case, the filter network is of the known "unity-gain single-feedback" type, where the required constant current source (for the associated buffer circuit) is formed by active devices rather than simple resistors. In summary, for both the buffer module and the crossover filter module, only circuits containing common cathode / common emitter / common source circuits are used, for tube / junction transistor / MOSFET implementations, respectively.

[0055] Active cooling of circuit elements (but not tubes) at room temperature reduces electroacoustic noise. Therefore, the present invention should be implemented using only solid-state active devices.

[0056] If active cooling is avoided, the best low electro-acoustic noise effect can be achieved by considering the active speaker drive scheme shown in Figure 5. 5. The low-frequency output stage uses a fully solid-state output, avoiding the use of multiple pairs of tubes in parallel to realize the output stage, making it easier to provide the required output power.

[0057] For low frequencies, transistors are used to implement the corresponding output stages, similar to the approach taken by Robling in U.S. Patent 9,306,510 B1 (2016), "Frequency-Dependent Dual Solid-State and Vacuum Tube Power Amplifier - Partial Instrument Amplifier." The latter is suitable for bass guitars, which typically use bidirectionally driven speakers, while in Robling's patent, these speakers are actively driven. However, the technical problem solved by that patent is different from that of the present application. For example, Robling's patent does not mention the structural characteristics of the circuit elements, nor does it mention appropriate circuit operating conditions that help reduce electroacoustic noise.

[0058] Unlike the Robling patent, this invention is also fully applicable to electric guitar (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-range loudspeaker, as was the case with earlier guitar systems emulated by prior art. Using an active loudspeaker driver allows for uncompromising electro-acoustic noise reduction: the speaker is connected to the amplifier without any filtering networks or transformers, and the power output stage uses relatively high tube bias currents. It is best to use a solid-state output module to drive the lowest-frequency woofer, thus avoiding the use of more than one pair of power tubes connected in parallel in the output stage, which would result in excessive network power dissipation and increase cost and size. Therefore, tube amplifier modules are used only in circuits operating above 200 Hz to 300 Hz.

[0059] The following topics contribute to a better understanding of the characteristics of the present invention and highlight its substantial differences from the patents whose technical problems (i.e., producing lower measurement distortion) are in any case completely different from the present application (aims to suppress a type of noise that can only be detected by comparative listening tests).

[0060] Rozemblit's US Pat. No. 5,604,461A (1997), "Transformerless Output Vacuum Tube Audio Amplifier," presents an audio amplifier that, among other requirements, must not use capacitors for interstage coupling, whereas similar coupling is compatible with the solution to the problem presented in this application. Furthermore, Rozemblit's patent presents a "long-tailed pair" circuit using a simple resistor as a constant current source, whereas in this specification, the constant current source includes an active device. For example, Takehara's US Pat. No. 4,241,313 (1980), "Audio Power Amplifier," proposes the latter possibility, but neither of these patents provides any description of the structural characteristics of the circuit components.

[0061] In King's patent WO 87 / 07554 (1987), "Sound Reproduction System," the amplifier is connected to the loudspeakers via a passive crossover filter network consisting of resistors, capacitors, and even inductors. The resistors are of a linear type, suitable for the power applications required by passive crossovers. However, these resistors do not require specific structural characteristics, only that they meet the quality standards of the particular application. Similar requirements apply to the type of capacitors used in the filter network. In contrast, in the present application, as described above, the loudspeakers must be connected directly to the amplifier. If multi-way loudspeaker driving is required, this is achieved actively, by installing a filter stage in the amplifier, constructed to the same standards as those discussed herein for suppressing electroacoustic noise. Another important feature of the invention described herein is the specification of parameters (mass and geometry) relating to the construction characteristics of the passive and active components used in the circuit.

[0062] Figure 3 shows a schematic diagram of an audio amplifier specifically designed for guitars, with features that minimize electroacoustic noise and can drive any type of speaker.

[0063] In this embodiment, the voltage amplifier stage is implemented using tubes, while the power output stage utilizes solid-state devices. Active cooling of at least 10 degrees Celsius for the final stage components further reduces electroacoustic noise. By extending cooling to other components, the entire circuit can be implemented using solid-state devices, significantly reducing the target noise.

[0064] If the input signal is unbalanced (as is often the case with guitars), it is fed into the amplifier's gain potentiometer (1). To significantly reduce electroacoustic noise, the potentiometer used in the present invention employs a switch with at least 12 levels, with one or two groups selected depending on whether a single-channel or balanced signal is being processed. As described above, a polarized wirewound resistor is mounted on the switch, acting as a potentiometer.

[0065] The differential voltage amplifier structure (tubes 11, 12 and current source comprising device 31) forms a balanced signal, which is a prerequisite for obtaining low electroacoustic noise (in combination with the other technical options described in this article). The figure shows an optional cascade connection, further connecting the voltage amplifier stage (tubes 11', 12' and current source comprising device 31') to obtain the required gain. This stage is then AC-coupled to the next buffer stage (40), the buffer circuit of which is of the type shown in Figure 4, i.e., comprising a device (13) equipped with a corresponding constant current source, which is composed of an active constant current source device (33).

[0066] To achieve lower electroacoustic noise, it is important to use Figure 4The same type of buffer circuit performs the buffering and equalization functions of stage 40, and the polarization function of stage 400 (see Figure 3 ), the circuit ultimately requires two or more amplifier embodiments ( Figure 5 ) provides frequency division function.

[0067] Specifically, in order to obtain the active drive Figure 5 To achieve the necessary response accuracy of the crossover filter for the loudspeaker shown, the filter block uses the technical note "Unity-Gain Single Feedback Implementation" (see: Introduction to Modern Network Theory, McGraw-Hill Education, 2014) because it uses only buffer stages (instead of operational circuits with appropriate voltage gain). These buffer stages use discrete active components such as Figure 4 With this choice, the amplifier stage is avoided, since it must be of the differential type, which means a more complex circuit and a higher number of components, resulting in an increase in the target noise.

[0068] A solution is required for at least two ways to drive the speaker (see Figure 5 ), for example, when the circuit components are not actively cooled. In this case, as mentioned above, the crossover frequency should be around 200 Hz - 300 Hz to avoid using multiple tube pairs in an output stage 60 designed for frequencies above this frequency. This choice is particularly useful for instruments that produce harmonics starting from very low frequencies, such as double bass and bass guitar, as well as certain wind instruments that are often amplified in jazz.

[0069] In the embodiment of the present invention as a guitar amplifier, the module 400 with the crossover filter function (only required when using multiple output power modules, such as Figure 5 The 12-bit ...

[0070] When using the circuit in conjunction with a distortion module, the distortion module is inserted via the segmented connections of states 40 and 400 and must be considered using the same criteria discussed herein for reducing electro-acoustic noise. For musicians, using a distortion device is an essential option for creating effects, such as when using an electric guitar, as described above. In guitar amplifiers, the distortion function is typically achieved by activating a distortion device connected to the amplifier's external loop (FX loop), or by activating a distortion module embedded within the amplifier, as shown in the prior art in Figures 1 and 2.

[0071] One method of artificially altering the signal from an instrument's pickup is based on the concept of a square wave waveform, achieved by operating under strong amplification. Thus, starting with a strong signal, the sinusoidal signal becomes a trapezoidal signal, then gradually transforms into a square wave with increasing amplitude. This corresponds to the addition of artificial harmonic components—unrelated components of the audio signal. The resulting overdrive pattern achieves increasingly pronounced distortion, moving from a crunching sound to a dominant mode and even a "fuzz" sound. Besides squaring the waveform, guitarists sometimes choose other ways to alter the sound, such as using a suitable oscillator circuit to implement vibrato. A more common option is reverb, or a reverb function, originally developed by Hammond and later licensed to Fender and other instrument manufacturers. Reverb is implemented by feeding the signal from the instrument into the input of an amplifier. The signal is pre-amplified and split into two paths. The first path remains unchanged (the "dry" signal), while the second path is connected to a buffer stage, which feeds the signal into the input of a device consisting of one or more springs connected to two electroacoustic transducers: the input and output of the reverb device. Due to the resonance of the springs, the signal output from the device is "wet," which is then mixed with the "dry" signal.

[0072] As mentioned above, the buffer stage 40 of the amplifier chain can drive a waveform squaring device or other types of distortion tools, such as a spring unit for reverberation mode. Even the latter type of sound exhibits a unique characteristic of the present invention, namely, low electroacoustic noise, resulting in better sonic performance. This applies when using the same circuit and component standards as described above. The circuitry required for amplification, buffering, and dry / wet signal balancing must utilize: i) the same type of balanced signal circuitry; ii) a differential amplifier stage; iii) a buffer circuit suitable for balanced signals; iv) no negative feedback, and primarily appropriate passive and active components.

[0073] The circuit shown in Figure 5 is easily generalizable to construct low-electroacoustic-noise systems with more than two active channels. It is particularly suitable for driving music studio loudspeakers in active mode. The loudspeakers are driven in phase using a co-inverting design to minimize overlap in the frequencies handled by the two loudspeakers, thereby optimizing the overall phase response.

[0074] One or more modules of the high-frequency output power stage (see Figure 5) are based on the original Circlotron tube configuration. The low-frequency module is implemented using transistors, but differs from the Bongiorno module for the following reasons: i) it uses class AB polarization, and ii) it provides a standard voltage multiplication network rather than the one used by Bongiorno. The solid-state output stage (51) is intentionally based on bipolar junction transistors, which have the advantages of lower cost, higher collector current handling capability, and lower crossover distortion under load compared to MOSFETs. This is required for the Circlotron class AB operation.

[0075] On the other hand, the output transistor driver stage is implemented using MOSFETs. This has the advantage that the load on the corresponding voltage amplifier stage is low even if it is implemented using electron tubes, as shown in Figure 3.

[0076] To compensate for the natural frequency roll-off of such amplifier circuits without negative feedback, module 40 (and module 400) uses a frequency equalization that is typically smaller in tube designs and larger in solid-state implementations of voltage amplifier stages. This is accomplished using simple RC cells with resistor dividers, each made from components with the aforementioned structural characteristics.

[0077] The bias current of the power tubes is obtained by selecting the resistor dividers included in the filter and bias module (400) so as to obtain a sufficiently high bias current (of the order of several hundred milliamperes for audio power triodes). As mentioned above, this relatively high current is necessary to make the electrode system of the tube (and the associated support components and heat sink) highly resilient to the stresses occurring on a microscopic scale. For the same reason, the polarization currents of the tubes that may be used in the driver, filter and separation stages are also slightly lower than the maximum conventional values expected for these tubes.

[0078] Output power transistors 51 and 52 are also biased via appropriately selected resistor dividers within module 400. Thermal stability of the output power transistors is achieved using a simple diode array located at the thermal contacts of the transistor housings, along with a voltage multiplier circuit. A high DC voltage source (approximately 80 V) is selected to power the output transistors, while the bias current is relatively low (approximately 30 mA). Both options are effective in reducing electroacoustic noise.

[0079] In general, in addition to the power supply's electrolytic filter, at least one capacitor with the aforementioned characteristics should be connected close to the amplifier circuit to reduce electroacoustic noise at the output. Finally, a transistor with stabilizing base / gate resistors (approximately 100 ohms) is also essential. In some cases, in tube applications, these resistors can be replaced with short circuits to reduce electroacoustic noise.

Claims

1. An amplifier for a low-noise electric musical instrument, which is implemented by an electron tube or solid-state device, comprising the following parts: a) an input stage, comprising at least a first and a second input terminal device (10, 20) for receiving at least one input signal; b) a preamplifier stage, comprising at least a portion having a long tail pair circuit and a ground terminal (Gr); c) a buffer filter stage (40), comprising at least a first and a second input terminal (41, 42) and at least a first and a second output terminal (43, 44); d) a filter bias stage (400), comprising at least a first and a second input terminal (401, 402) and at least a first, a second, a third and a fourth output terminal (403, 404, 405, 406); d) an output stage, comprising at least a floating bridge module (50), operating in at least a first frequency range and comprising at least a first and a second DC power supply (511, 512); e) at least a first and a second output terminal device (A10, A20) for connecting one or more speakers operating in the first frequency range, The electron tube comprises at least one first part, called the anode, at least one second part serving as a mechanical support for the anode, and at least one third part for heat dissipation of the anode. The portion of the preamplifier stage having the long tail pair circuit includes: i) first and second preamplifier means (11, 12), each comprising 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 means (31), the constant current source means comprising a power supply terminal (G), a control terminal (H) and an output terminal (I); The first and second input terminals (A, B) of the first and second preamplifiers (11, 12) are respectively connected to the same first DC voltage source (21) through a connecting device, and the first DC voltage source (21) uses the ground terminal (Gr) as a reference point; The control terminal (C) of the first preamplifier (11) is connected to the input terminal device (10) via a connecting device; The first and second output terminals (E, F) of the first and second preamplifiers (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 to a second DC voltage source (22) via a connecting device (Ga), and the second DC voltage source (22) uses the ground terminal (Gr) as a reference point; the control terminal (H) of the constant current source device (31) is connected to the second DC voltage source (22) via a connecting device (Ha); The buffer filter stage (40) comprises at least one buffer device (13) and at least one constant current source, wherein the constant current source comprises a constant current source device (33), the buffer device (13) comprises an input terminal (L), a power terminal (N) and an output terminal (P), the constant current source device (33) comprises a power terminal (R), a control terminal (T) and an output terminal, and the power terminal (N) of the buffer device (13) is connected to a third DC voltage source (23) of a reference ground terminal (Gr); The output terminal (P) of the buffer device (13) is connected to the output terminal of the constant current source device (33) of the buffer filter stage (40) via a connecting line; The power supply terminal (R) of the constant current source device (33) is connected to the second DC voltage source (22) via a connecting line (Ra); The control terminal (T) of the first constant current source device (33) is connected to the second DC voltage source (22) via a connecting line (Ta); The first and second output terminals (43, 44) of the buffer filter stage (40) are connected to the first and second input terminals (401, 402) of the polarization filter stage (400), respectively; The first floating bridge output module (50) comprises at least first and second output devices (51, 52), each output device comprising 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) being connected to the first and second output terminals (404, 403) of the filtering and polarization stage (400) via connecting means, respectively; The first DC power supply (511) is connected between the power terminal (B1) of the first output device (51) of the first output module (50) and the output terminal (C2) of the second output device (52) of the first output module (50); The second DC power supply (512) is connected between the power terminal (B2) of the second output device (52) of the first output module (50) and the output terminal (C1) of the first output device output (51) of the first output module (50); The second DC power supply (512) is connected between the power supply terminal (B2) of the second output device (52) of the first output module (50) and the output terminal (C1) of the first output device output (51) of the first output module (50); the output terminal (C1) of the first output device output (51) of the first output module (50) The first and second output terminal devices (A10, A20) are respectively 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), at least one portion of the amplifier comprises at least one potentiometer, a capacitor or a resistor, the resistor being of a wire-wound type, at least a majority of which has a circular cross-section and a cross-sectional dimension greater than or equal to 15 thousandths of a millimeter.

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

3. The amplifier of claim 1, wherein the potentiometer is made of a wirewound resistor, wherein the cross-sectional area of the wire is equal to or greater than 0.015 mm.

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

5. An amplifier according to claim 1, wherein the output stage comprises at least one second floating bridge output module (60) operating in at least a second frequency range outside the first frequency range, the second floating bridge output module (60) comprising a third DC power supply (611) and a fourth DC power supply (612) and third and fourth output terminal means of the amplifier (A20, A21) for connecting one or more loudspeakers driven in the second frequency range; The second floating bridge output module (60) comprises first and second output devices (61, 62), each output device comprising first and second input terminals (D1, D2), first and second power 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 to the third and fourth output terminals (406, 405) of the filter and polarization stage (400) respectively via connecting means; The third DC power supply (611) is connected between the power terminal (E1) of the first output device (61) of the second floating bridge output module (60) and the 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 the power terminal (E2) of the second output device (62) of the second floating bridge output module (60) and the 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 the third and fourth output terminal devices of the amplifiers (A20, A21) through connectors, respectively.

6. The amplifier of claim 1, wherein at least one of the first, second and third parts of the electron tube is curved, and an area of the curved surface accounts for at least one third of the total area of the part.

7. The amplifier of claim 1, wherein a material thickness of at least one of the first, second, and third portions of the electron tube is greater than 0.1 mm.

8. The amplifier circuit of claim 1, wherein the bias current of at least one of the electron tubes is at least equal to two-thirds of the maximum value of the center design value of the electron tube.

9. The amplifier of claim 1, wherein at least one of the output devices of the output module of the output stage is implemented in a solid state and has a bias current of no more than fifty milliamperes.

10. The amplifier according to claim 1, comprising a heat pump device, the heat pump device comprising a module equipped with a first portion absorbing heat and a second portion emitting heat to a room, and first and second power supply terminals connected to a power supply, a housing of at least one of the devices and components other than an electron tube included in at least one portion of the amplifier being maintained at a temperature of at least five degrees Celsius lower than room temperature by direct or indirect contact of the housing with the first portion of the heat pump device absorbing heat.

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