A phantom-powered transistor electronic device for reducing impedance and altering the presentation of an audio signal for long-distance wired transmission.

Abstract

This utility model relates to the field of musical electronic equipment, specifically to means for wired transmission of a weak audio signal susceptible to electromagnetic interference from a musical instrument, such as an electric guitar, to a preamplifier or sound mixing console over distances of tens, even hundreds, of meters. The transistor electronic device with phantom power for reducing impedance and modifying the audio signal's presentation for long-distance wired transmission is a symmetrical bridge current circuit consisting of two current branches, implemented using discrete active elements—transistors. Phantom (parasitic) power to the device is supplied via a balanced line from a voltage source physically located in the remote end equipment connected to the device, and the change in current in these branches is converted into a difference in alternating voltage at the balanced output.The technical result of the claimed utility model is the creation of a new, highly specialized circuit topology for symmetrical current branches, unique to diode boxes, implemented in circuit diagrams using discrete active electronic components—transistors. This allows for a radical reduction in the current consumed by the device from the phantom power source while maintaining and even significantly improving the key electrical parameters compared to similar devices. 10 fig.

Description

[0001] Technical field

[0002] The utility model relates to the field of musical electronic equipment technology, namely to means for wired transmission over many tens, up to hundreds of meters, of a weak audio signal susceptible to electromagnetic interference from a musical instrument, for example, from an electric guitar to a preamplifier or a sound engineer's mixing console.

[0003] Technology Level

[0004] Di-boxes (DI boxes, direct input boxes) are a group of electronic devices known since the 1960s in the music industry and show business for converting unbalanced (linear, asymmetrical) output audio signals from electronic musical instruments (sources) with high internal impedance into balanced (differential) audio signals from low-impedance (low-ohm) sources. Di-boxes are commonly used in recording studios and concert venues. They minimize distortion and interference that can occur when transmitting signals from high-impedance sources over long distances via cable.

[0005] Phantom (parasitic) power is a method of supplying DC voltage to a microphone or other audio equipment via signal wires, while capacitors are used to separate the AC component of the audio signal. The permissible current consumption of the equipment from a standard phantom power source is very low (no more than 10 mA).

[0006] High-quality guitar pickups have a high output impedance of a non-differential useful audio signal, its variable potential difference (voltage) is formed at two terminals of a multi-turn inductor coil - a sensor that converts the mechanical vibrations of guitar strings into an electrical signal.

[0007] When organizing the electrical communication between a musical instrument and a mixing console using a long two-wire line, which has a priori low noise immunity, a noisy audio signal will inevitably be received at the receiving end without the use of a DI box.

[0008] There are passive, active, and active-passive types of DI boxes.

[0009] The passive type of dibox in general is a balanced transformer, also called a “balun” (Fig. 1).

[0010] An unbalanced (non-differential) source signal is fed to the primary winding of a transformer, one terminal of which is grounded. The secondary winding of the transformer has a grounded tap at the center. This creates identical-amplitude but antiphase (180° shifted, inverted) analogs of the input signal at its outer terminals. Together, they now represent a balanced (differential) source signal relative to ground.

[0011] The electrical impedance of the two signal conductors relative to ground becomes balanced (i.e., equal). The useful signal is then transmitted over the three wires of the balanced line.

[0012] Therefore, the surrounding industrial interference of industrial frequency 50 Hz or other frequencies will be induced equally, in the same phase and with the same amplitude, onto two balanced signal wires of the communication cable.

[0013] Such common-mode interference can be almost completely suppressed at the input of a mixing console by conventional differential amplifier circuits, since they amplify the useful voltage difference between two out-of-phase input signals. Therefore, the induced interference, which always arrives at the input of such an amplifier in phase, is eliminated, and the useful signal is doubled in amplitude.

[0014] In addition, the low output impedance of the DI boxes ensures good matching of the audio signal source with the low-impedance balanced microphone input of the mixing console.

[0015] The main disadvantages of passive dibox circuits are:

[0016] - the difficulty in achieving precise matching of the parameters of the balanced transformer windings during mass industrial production, which greatly affects the degree of common mode interference suppression;

[0017] - dips in the “jagged” transfer amplitude-frequency characteristic of an ordinary balanced transformer, especially in the high audio frequency range, due to its structurally non-ideal core and windings, the resistance of which is of an inductive nature (depending on the frequency of the alternating voltage of the converted audio signal);

[0018] - an inevitable reduction in the amplitude of the signal voltage at the output of the device during transformation, which increases the output current, but with a physically unchanged total power transmitted by the transformer;

[0019] - high cost of manufacturing a balanced transformer.

[0020] An example of a passive dibox is the JDI model device from Radial Engineering, Canada, presented on the website of this manufacturer on the Internet (https: / / www.radialeng.com / product / jdi).

[0021] The active type of DI box assumes a similar conversion of the input audio signal to that described above using electronic circuitry methods, but without the use of a transformer.

[0022] In a broad sense, an active DI box performs a sequential or combined pre-amplification of the input audio signal, its inversion, and a reduction in the impedance of the output, which has now become a two-component differential signal.

[0023] The applicant of this utility model is aware of one such full-fledged device with phantom power supply presented on the world market - this is the J48 model of the above-mentioned Canadian company (https: / / www.radialeng.com / product / j48).

[0024] Other active diboxes considered by the applicant are either connected to a separate network power supply or require the use of galvanic cells (batteries) or accumulators for their operation.

[0025] At the same time, a large number of active-passive dibox models have been sold worldwide, which, along with transistors and microcircuits, also contain a balanced transformer, for example: DN100 by Klark Teknik, UK (https: / / www.klarkteknik.com / product.html?modelCode= 0809-AAR); AR-133 by Harman Pro Group (BSS Audio), USA (https: / / bssaudio.com / en / products / ar-133).

[0026] Some manufacturers call their mixed designs “active” diboxes, which is unjustified and incorrect in the opinion of the applicant.

[0027] Unfortunately, all such diboxes partially inherit the shortcomings of simple passive circuits created exclusively on a balanced transformer.

[0028] The global manufacturers of various types of di-boxes found by the applicant of this utility model have chosen to maintain the secret of production (know-how) - they do not disclose the circuit and technological designs of their electronic devices.

[0029] The applicant's relevant patent search for a fully active (transformerless) di-box in the leading countries of the world did not yield any positive results.

[0030] However, Radial Engineering reports that its J48 DI box is built with low-noise operational amplifier chips, as stated in the specifications on the company's website (https: / / www.radialeng.com / product / j48 / specifications), and can also be seen in the third photo on the website's web page (https: / / www.radialeng.com / product / j48 / features).

[0031] The applicant considers this model as a prototype.

[0032] Its main electrical parameters, specified by the manufacturer in the specification, are as follows:

[0033] - frequency range from 20 to 20,000 Hz;

[0034] - dynamic range 109 dB;

[0035] - harmonic distortion coefficient 0.002%;

[0036] - input impedance 220 kOhm;

[0037] - output impedance 200 Ohm;

[0038] - self-noise level -99 dB.

[0039] Radial Engineering does not specify the current consumed by the prototype in its specifications.

[0040] Therefore, the applicant believes that due to the insufficient current supplied by the standard phantom power supply, the J48 DI box is unable to operate reliably (while maintaining the declared characteristics) at a low input signal level, as well as with a long communication line to the mixer (close to 100 meters).

[0041] Since a modern active DI box can be a fairly complex electronic circuit consisting of many individual power-consuming components, the problem of providing it with sufficient power supply is key when creating a fully active DI box.

[0042] Specific stage conditions, as well as the utilitarian requirements of the relevant technical specialists, do not require the presence of stabilized power supplies for DI boxes, and most importantly, additional wires to provide electricity to their circuits on stage.

[0043] Therefore, the possibility of using low-current phantom power from a mixing console via a balanced line - two antiphase signal wires relative to one ground wire - becomes an urgent task.

[0044] The 48V power supply is a built-in option for microphone inputs (XLR, DIN-327 connectors) on standard mixing consoles. However, as previously noted, the current consumption of all equipment from the phantom power supply is limited to 10 mA, as regulated by the P48 standard (German national standard DIN 45596 (1981) "Microphones; phantom powering"; international standard IEC 61938 (1996) "Multimedia systems - Guide to the recommended characteristics of analogue interfaces to achieve interoperability").

[0045] Low-noise operational amplifiers with sufficient processing speed to handle high-quality audio signals contain dozens of transistors. Due to the physical nature of p-n junctions on their semiconductor crystals, an inevitable voltage drop occurs, which, in both static and especially dynamic modes of amplifier operation, leads to a loss of the meager available electrical energy—the generation of useless thermal power in the transistors.

[0046] According to the applicant, constructing an active di-box with phantom power using operational amplifier chips wastes their potential. Furthermore, such a circuit requires a step-up voltage converter, which, in addition to significantly complicating the circuit, negatively impacts the noise level of the entire device, which is already at the limits of its design (without any reserve for current consumption, which is extremely tightly limited by a typical phantom power supply).

[0047] It should be noted that truly high-quality specialized operational amplifier microcircuits that meet the requirements of high-fidelity sound reproduction standards - Hi-Fi (GOST 24388-88 "Household audio frequency signal amplifiers. General specifications"; National standard of Germany DIN 45500-1 (1974) "High fidelity audio equipment and systems; minimum performance requirements"; International standard IEC 60581-1 (1977) "High fidelity audio equipment and systems; Minimum performance requirements"), have only their own current consumption of about ten milliamperes - information sheets (datasheet): NJM4580 microcircuit (https: / / static.chipdip.ru / lib / 774 / DOC059774679.pdf), OPA132, OPA2132, OPA4132 microcircuits, high-speed operational amplifiers with an input field-effect transistor transistor (https: / / static.chipdip.ru / lib / 204 / DOC000204716.pdf), OPA161x microcircuits, high-quality operational amplifiers for processing audio signals with an input bipolar transistor of the SoundPlus™ series (https: / / static.chipdip.ru / lib / 433 / DOC009433608.pdf).

[0048] Also, to build an active dibox, you need at least two separate operational amplifiers (possibly, of course, included in the same microcircuit).

[0049] In view of this, the circuit design of the Canadian J48 dibox should be considered a compromise, made using non-specialized general-purpose microcircuits and, probably, of mediocre quality.

[0050] Disclosure of Utility Model

[0051] The technical result of the claimed utility model is the creation of a new, highly specialized circuit topology, unique to di-boxes - in the form of symmetrical current branches, implemented in basic electrical circuits on discrete active electronic components - several transistors, which made it possible to radically reduce the current consumed by the device from the phantom power source while maintaining and even significantly improving the main electrical parameters in comparison with analogues.

[0052] The claimed technical result is achieved by a transistor electronic device with phantom power for reducing impedance and changing the presentation of an audio signal for the purpose of its wired transmission over a long distance, wherein the topology of the device is a symmetrical bridge current circuit consisting of two current branches, implemented on discrete active elements - transistors, phantom (parasitic) power supply of the device is carried out along a balanced line from a voltage source physically located in the remote terminal equipment connected to the device, and the change in the currents of the said branches is converted into a difference in alternating voltages at the balanced output.

[0053] Brief description of drawings

[0054] Fig. 1 shows the schematic diagram of the general concept of a passive type dibox.

[0055] Fig. 2 schematically shows the internal structure of the mixer's balanced microphone input.

[0056] Fig. 3 shows the circuit diagram of variant D of the utility model of an active dibox with phantom power supply on ten separate transistors.

[0057] Fig. 4 shows the circuit diagram of variant J of the utility model of an active dibox with phantom power on fourteen separate transistors.

[0058] Fig. 5 shows the functional diagram of the claimed device.

[0059] Fig. 6 shows the architecture - equivalent circuit of the claimed device.

[0060] Fig. 7-8 show photographic images of assembled double-sided electronic printed circuit boards of di-boxes with phantom power on ten separate transistors.

[0061] Fig. 9-10 show photographic images of assembled double-sided electronic printed circuit boards of di-boxes with phantom power on fourteen individual transistors.

[0062] Implementation of a utility model

[0063] The applicant has developed a utility model of an active di-box with phantom power supply using only ten individual transistors in variant D or fourteen transistors in variant J; their basic electrical circuits, created in the cloud-based CAD system for automated electronic design EasyEDA (https: / / easyeda.com), are presented in this application (Fig. 3 and Fig. 4, respectively).

[0064] The optional addition of JFET transistors (Q7, Q8) and matching bipolar transistors (Q9, Q10) to the input stages of variant J does not in any way affect the integral essence of the utility model in any of the two variants (D and J), but is determined by taste, emotional psychoacoustic (see I. A. Aldoshina, Roy Pritts. Musical acoustics. Textbook for higher educational institutions. - St. Petersburg: Composer, 2004) preferences of a number of musicians in their subjective perception of the overall sound picture of the reproduced audio signal, which has undergone electrical transformation with slight complex distortions inherent in field-effect transistors (nonlinear circuit elements with a unique, multifactorial physical characteristic).

[0065] Music creators usually use the "warm" sound of the J DI box when playing electric guitars without an electronic preamplifier - "passive" instruments, and the sound of the D DI box when playing "active" instruments (keyboard electronic instruments, electric guitars with a preamplifier).

[0066] The main electrical parameters of the created utility model are as follows:

[0067] - frequency range from 10 Hz to 3.5 MHz;

[0068] - dynamic range 117 dB;

[0069] - harmonic distortion coefficient <0.001%;

[0070] - input resistance ≥4.7MΩ;

[0071] - output impedance <33 Ohm;

[0072] - self-noise level -110 dB;

[0073] - current consumption 4.6 mA.

[0074] The stated characteristics of the dibox proposed by the applicant significantly exceed in all respects the J48 dibox from Radial Engineering.

[0075] In Fig. 5, a linear audio signal is fed to the inputs of identical device blocks (A1 and A2), the current of which flows through two branches (bipolar structure) forming the “hot” and “cold” antiphase parts of the output differential signal relative to zero (ground).

[0076] These blocks (branches) are also connected to each other symmetrically by resistors: R k (position designation on both circuit diagrams is R31), R Vhot (R13), R Vcold (R14) and at the output through the terminal equipment, forming current flow circuits in a closed electrical circuit.

[0077] To the common connection point of resistors R Vhot and R Vcold, The parametric voltage stabilizer (A4) is connected to the positive potential of the input circuits, which also dampens excess power in the entire balanced symmetrical bridge current circuit of the electronic device. LED3, connected in the forward direction, is used as a stabilizer here.

[0078] The example of block A1 in this diagram shows that it consists of a current generator (A1.1), a modulator (A1.2), a combined transistor cascade (A1.3), a current-to-voltage converter (A1.3.1), and a buffer to reduce the output impedance (A1.3.2).

[0079] The integrating circuit for the soft start of the current generators of both branches of the circuit (A5) prevents the appearance of sound artifacts (sharp clicks) on the terminal acoustic systems when turning on or switching the device.

[0080] The self-balancing topology of the dielectric box under consideration is fundamentally based on Kirchhoff's first law, the law of currents (their algebraic equality to zero at a node in an electrical circuit). This eliminates the need for any type of explicit feedback for automatic control.

[0081] Generator A1.1 produces a stable current. Next, in cascade A1.2, amplitude modulation of this current by the input signal voltage occurs, described by formula (1):

[0082] I(t) = I0- U in (t) / k (1),

[0083] where I(t) is the output current of the modulator; I0 is the stable current entering the modulator; U in (t) is the audio signal voltage changing over time; k is the modulation coefficient determined by the value of the resistor Rk .

[0084] This resistor R k basically sets the initial balance of currents flowing in blocks A1 and A2 to obtain phase (“hot”) and phase-inverse (“cold”) signals symmetrical relative to the ground at the output of the dibox.

[0085] Then, in the A1.3 cascade, the current modulated by the input audio signal is converted into a control voltage for the emitter follower - a current amplifier on a composite Sziklai transistor, which “accelerates” the current to the output of the DI box (its point of highest potential of the phantom supply voltage), thereby reducing the output impedance of the entire device.

[0086] Fig. 6 shows the architecture - the equivalent circuit diagram of the di-box, revealing the paths of current flow through the electrical loads of the two branches of its circuit-technological design, and how exactly the change in the current difference in these branches is converted into a voltage difference at the balanced output of the device.

[0087] The variable resistances in this diagram indicate controlled electrical loads - the corresponding transistor cascades of the device nodes.

[0088] Varistor R ST The equivalent circuit shows the dynamic resistance of the parametric voltage stabilizer (A4).

[0089] Current generators A1.1 and A2.1 are built on transistors Q12, Q13 (in both versions of dibox D and J).

[0090] The input stages (current modulators A1.2, A2.2) are implemented in version D on transistors Q6, Q16 and Q10, Q2, and in version J on Q7, Q21, Q5, Q9 and Q8, Q6, Q2, Q10, respectively.

[0091] In variants D, J, the output combined stages A1.3 and A2.3 contain transistors Q15, Q3 and Q4, Q1.

[0092] The industrial applicability of the disclosed utility model is also proven by photographs of mounted double-sided electronic printed circuit boards of the diboxes of variant D (Fig. 7, Fig. 8) and variant J (Fig. 9, Fig. 10), developed in the EasyEDA CAD system and mass-produced under trademark No. 1150245 registered in the Russian Federation on September 15, 2025, in class 9 of the International Classification of Goods and Services, the copyright holder of which is the applicant of this utility model.

Claims

A transistor electronic device with phantom power for reducing impedance and changing the presentation of an audio signal for the purpose of its wired transmission over a long distance, characterized in that the topology of the device is a symmetrical bridge current circuit consisting of two current branches, implemented on discrete active elements - transistors, phantom - parasitic power of the device is carried out along a balanced line from a voltage source physically located in the remote terminal equipment connected to the device, and the change in the currents of the said branches is converted into a difference in alternating voltages at the balanced output.

Images