Audio Preamplifier Research Articles

A 87 dB SNR and THD+N 0.03% HiFi Grade Audio Preamplifier

This paper presents a significant contribution to high-fidelity audio technology through the comprehensive design and implementation of an advanced audio-grade preamplifier integrated with a high-performance digital-to-analog converter (DAC). The versatility of the digital section allows seamless integration of audio sources from Universal Serial Bus (USB), Bluetooth, or Sony-Philips Digital interface (SPDIF). In addition, the preamplifier accommodates various analog sources, offering flexibility to users. The unique architecture features an innovative resistor network-based DAC and precision components in the analog section, paving the way for achieving unparalleled audio fidelity. The measured distortion values are remarkably low, with a total harmonic distortion plus noise (THD+N) of only 0.03%. Furthermore, the system exhibits a signal-to-noise ratio (SNR) of 87 dB, comparable to industry benchmark. The hardware design sections went into meticulous details, providing an in-depth exploration of each block of the project. The inclusion of test and measurement data from the actual prototype enhances the credibility of the proposed work. This research not only showcases the theoretical operation of the preamplifier and DAC stage but also validates the practical implementation through many rounds of testing and validation. Our proposed work contributes to the field of high-fidelity audio by presenting a novel solution that is comparable to industry standards. The design’s adaptability to many different audio sources, coupled with robust performance metrics, positions it as a benchmark in the field of audio reproduction. The measurement results and findings presented in this paper are poised to influence future advancements in HiFi audio technology.

Tracking extraterrestrial signals using the Super SID and Radio JOVE kits

A 20.1MHz dipole radio telescope was assembled, characterized and tested to detect extraterrestrial signals from planet Jupiter. Two element dipole arrays were built for the detection of 20.1MHz radio emission from the Jupiter-Io interaction, strong solar burst, the galactic background and the transit of the galactic center. Using the specifications and the layout, the dipole array was constructed. The block diagram, the schematic diagram built for NASA was used to solder together the radio frequency band pass filter, audio Preamplifier and audio amplifier to make the radio JOVE receiver. This was characterized, tested and tuned by setting the tuning knob to 20.0MHz. The dipole antenna was connected to the receiver and a variety of radio frequency emissions were detected. These signals were captured on a personal computer via the radio Jupiter Pro 3.8.3 and radio skypipe 2.6.5 software compatible with windows 7 OS and has python programme which converts data from the sod format to ASCII format to conveniently analyzed them. The data locally captured was correlated with other stations of the world. Specifically the analyzed chart of 14th July 2022 shows a lot of similarities with that captured by radio telescope UNIVERSUM shared with the global web repository.

A 5-nV/√Hz Chopper Negative-R Stabilization Preamplifier for Audio Applications

This paper presents a low-noise and low-power audio preamplifier. The proposed low-noise preamplifier employs a delay-time chopper stabilization (CHS) technique and a negative-R circuit, both in the auxiliary amplifier to cancel the non-idealities of the main amplifier. The proposed technique makes it possible to mitigate the preamplifier 1/f noise and thermal noise and improve its linearity. The low-noise preamplifier is implemented in 65 nm complementary metal-oxide semiconductor (CMOS) technology. The supply voltage is 1.2 V, while the power consumption is 159 µW, and the core area is 192 µm2. The proposed circuit of the preamplifier was fabricated and measured. From the measurement results over a signal bandwidth of 20 kHz, it achieves a signal-to-noise ratio (SNR) of 80 dB, an equivalent-input referred noise of 5 nV/√Hz and a noise efficiency factor (NEF) of 1.9 within the frequency range from 1 Hz to 20 kHz.

100${+}$ dB A-Weighted SNR Microphone Preamplifier With On-Chip Decoupling Capacitors

This paper presents the design and realization of a gain-programmable microphone audio preamplifier that does not need external input-decoupling capacitors. Three possible preamplifier implementations with on-chip decoupling capacitors have been presented and compared in terms of audio quality performance, power consumption, and silicon area occupation. The chosen solution has been integrated in a 40-nm digital CMOS process with seven metal layers and a double gate-oxide option. Process fringe capacitors have been used to implement the internal decoupling, amplifying, and dc biasing functions. The active area is 0.19 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , whereas the power consumption is 330 μ W at a 1.5-V power supply. Measured dynamic range (DR) and maximum signal-to-noise-and-distortion ratio (SNDR) of approximately 105 dB A-weighted and 101 dB A-weighted, respectively, have been achieved for 0-dB gain and balanced inputs. The preamplifier can process both balanced and single-ended inputs, and its gain can be programmed from 0 to 19.5 dB in 1.5-dB/steps with acceptable performance losses.

Automated Physical Modeling of Nonlinear Audio Circuits for Real-Time Audio Effects—Part II: BJT and Vacuum Tube Examples

This is the second part of a two-part paper that presents a procedural approach to derive nonlinear filters from schematics of audio circuits for the purpose of digitally emulating musical effects circuits in real-time. This work presents the results of applying this physics-based technique to two audio preamplifier circuits. The approach extends a thread of research that uses variable transformation and offline solution of the global nonlinear system. The solution is approximated with multidimensional linear interpolation during runtime to avoid uncertainties in convergence. The methods are evaluated here experimentally against a reference SPICE circuit simulation. The circuits studied here are the bipolar junction transistor (BJT) common emitter amplifier, and the triode preamplifier. The results suggest the use of function approximation to represent the solved system nonlinearity of the K-method and invite future work along these lines.

Audio limiter using voltage multiplexed feedback

An audio system having a main chassis including an audio preamplifier and a remote chassis including a power amplifier has a clipping level detector circuit in the remote chassis for detecting the onset of clipping by the power amplifier and has a gain control element in the main chassis for controlling the gain of the preamplifier. An extra control line in the wiring harness connecting the main chassis and the remote chassis is avoided by multiplexing the clipping signal and the mute control signal on a single control wire.

A high-quality digital audio filter set designed by silicon compiler CATHEDRAL-1

The semi-automatic design and custom integration of a high-quality digital audio preamplifier filter set are described. The set consists of an offset filter, ten graphic equalizer sections, and a scratch filter with a worst-case overall signal-to-noise ratio of 10 dB. The silicon compiler CATHEDRAL-1 supports the design from specifications to layout. The combination of efficient synthesis tools with optimisation at all design levels leads to a very compact silicon integration, compared with a general-purpose signal processor approach. An experimental chip is described on which the offset filter, three equalizer sections, and the scratch filter are integrated. The silicon area is 243 mm/SUP 2/ in a conservative 6-/spl mu/m NMOS technology or 8 mm/SUP 2/ when scaling down to 3-/spl mu/m technology, allowing for functional densities up to 0.2 mm/SUP 2/ pole zero, comparable with area requirements for typical switched-capacitor filters. The total filter set requires only 20 mm/SUP 2/ in a 3-/spl mu/m NMOS technology, which demonstrates the potential for low-cost digital high-fidelity signal processing.

Ultrasonic fluid leak detector

A device for detecting ultrasonic noise, particularly such noise as generated by fluid leaks, includes a directional ultrasonic microphone, amplifiers and ultrasonic filters, an envelope detector, an audio preamplifier and filter, a level control, a meter, an audio power amplifier and speaker, and a phase shift feedback network connected from the output of the power amplifier to an input thereof. A switch is operable in a first setting to connect the power amplifier to the level control to convey the audio frequency amplitude envelope of the detected ultrasonic noise through the speaker or in a second setting to connect the power amplifier to the feedback network. A level detector is operatively connected to the level control and provides a control signal which is conducted to the feedback network. When the control signal exceeds a selected level, the feedback loop circuit is completed, whereby the power amplifier oscillates audibly through the speaker and gives audible indication of an ultrasonic noise. The components are enclosed in a pistol shaped housing for substantially single handed aiming and operation.

A Low-Cost AM-FM Radio Employing an Integrated Circuit

This paper demonstrates the possibility of reducing circuit complexity in an AM-FM radio by replacing the FM-IF amplifier limiter and detector as well as the audio preamplifier, with a monolithic linear integrated circuit, the µA717. The unconventional circuitry of the FM detector and low-voltage power supply and the elimination of audio switching between FM and AM operation are discussed in detail. The performance figures of the complete radio are given.