The State of Hollow State Audio in the Second Decade of the 21st Century
Vacuum-tube (or valve, depending upon which side of the pond you live on) technology spawned the Age of Electronics early in the 20th Century. Until the advent of solid-state electronics near mid-century, hollow-state devices were the only choice. But following the invention of the transistor (after their process fell to reasonable levels), within a couple of decades, the death of vacuum tubes was widely heralded. Yet here we are some five decades later, and hollow-state equipment is enjoying something of a comeback, especially in the music and high-end audio industries.
Many issues surround hollow-state audio:
Does it produce—as some claim—better sound? If so, is there science to back up these claims?
How do hollow-state circuits work?
How do you design hollow-state audio circuits?
If hollow-state equipment fails, how do you go about troubleshooting and repairing it?
Can we recreate some of the classic hollow-state audio devices for modern listening rooms and recording studios?
How can we intelligently modify hollow-state amplifiers to our taste?
These and other topics are covered in The State of Hollow State Audio.
Programming the Finite State Machine with 8-Bit PICs in Assembly and C
Andrew Pratt provides a detailed introduction to programming PIC microcontrollers, as well as a thorough overview of the Finite State Machine (FSM) approach to programming. Most of the book uses assembly programming, but do not be deterred. The FSM gives a structure to a program, making it easy to plan, write, and modify. The last two chapters introduce programming in C, so you can make a direct comparison between the two techniques. The book references the relevant parts of the Microchip datasheet as familiarity with it is the best way to discover detailed information.
This book is aimed at Microsoft Windows and Linux users. To keep your costs to a minimum and to simplify the toolchain, specific applications are provided as a free download to enable you to use an FTDI serial lead as the programmer. The assembler used is the open-source "gpasm". All programming can be done in a text editor. There are detailed instructions on how to perform the necessary installations on Windows, Linux Debian, and derivatives such as Ubuntu and Fedora. For programming in C, Microchip's XC8 compiler is used from the command line. In addition to the programming applications, two serial read and serial write applications can be used for communicating with the PICs from a computer.
A voltmeter project including practical instructions on building a circuit board from scratch is included. All theory is covered beforehand, including how to do integer arithmetic in assembly.
Two PICs are covered: the PIC12F1822 and the PIC16F1823. Both can run at 32 MHz with an internal oscillator. You do not need to buy a factory-made development board and programmer. With relatively inexpensive parts including a serial lead, microcontroller, a few resistors, and LEDs, you can get started exploring embedded programming.
Links
Updated Programmer
Easy and Affordable Digital Signal Processing
The aim of this book is to teach the basic principles of Digital Signal Processing (DSP) and to introduce it from a practical point of view using the bare minimum of mathematics. Only the basic level of discrete-time systems theory is given, sufficient to implement DSP applications in real time. The practical implementations are described in real time using the highly popular ESP32 DevKitC microcontroller development board. With the low cost and extremely popular ESP32 microcontroller, you should be able to design elementary DSP projects with sampling frequencies within the audio range. All programming is done using the popular Arduino IDE in conjunction with the C language compiler.
After laying a solid foundation of DSP theory and pertinent discussions on the main DSP software tools on the market, the book presents the following audio-based sound and DSP projects:
Using an I²S-based digital microphone to capture audio sound
Using an I²S-based class-D audio amplifier and speaker
Playing MP3 music stored on an SD card through an I²S-based amplifier and speaker
Playing MP3 music files stored in ESP32 flash memory through an I²S-based amplifier and speaker
Mono and stereo Internet radio with I²S-based amplifiers and speakers
Text-to-speech output with an I²S-based amplifier and speaker
Using the volume control in I²S-based amplifier and speaker systems
A speaking event counter with an I²S-based amplifier and speaker
An adjustable sinewave generator with I²S-based amplifier and speaker
Using the Pmod I²S2 24-bit fast ADC/DAC module
Digital low-pass and band-pass real-time FIR filter design with external and internal A/D and D/A conversion
Digital low-pass and band-pass real-time IIR filter design with external and internal A/D and D/A conversion
Fast Fourier Transforms (FFT)
Jan Didden created Linear Audio in 2010 and published 14 Volumes between 2010 and 2017. Each 200-page Volume contains on average 10 articles by expert authors in the field of audio, acoustics, and instrumentation. Whether you are interested in tube amplifiers, solid-state equipment, loudspeaker design, capacitor and resistor distortion or distortion measurement, you are certain to find helpful advice and interesting discussions. From beginner to advanced level, for the audio professional or the serious hobbyist, this ExpertCollection will advance your understanding and offer new perspectives on common issues. Bonus material included with this collection is a 5-part YouTube series on negative feedback as applied to audio by renowned author Jan Didden, and nine additional landmark audio articles and presentations. If you are seriously interested in audio, acoustics, and instrumentation, you can’t afford to miss this! The published material is indexed and fully searchable and will provide an almost limitless resource for many years to come. You can read about Linear Audio’s authors, and the Table of Contents of each Volume, at linearaudio.net.
Some Highlights from the contents Surround-sound decoder Compact amp Sampling rate converter Battery powered preamplifier Titan 2000 amplifier Crescendo Millennium amplifier Audio-DAC/ADC IR-S/PDFI receiver and transmitter High-End Power Amp Hi-fi Wireless Headset Paraphase Tone Control and more… Using Adobe Reader you are able to browse and search the articles on your computer, as well as print texts, circuit diagrams and PCB layouts.
Elevate your audio experience with the Douk Audio P6 mini Tube Preamplifier, a perfect blend of modern connectivity, HiFi sound quality, and vintage charm. Whether you're an audiophile or just starting your journey into high-quality audio, this compact yet powerful preamp offers everything you need.
Features
Versatile Connectivity: Supports Bluetooth 5.0, USB (U-Disk), and RCA connections, making it compatible with a wide range of devices such as phones, TVs, tablets, projectors, and computers. Plays lossless audio formats (APE, FLAC, WAV, WMA) and MP3 directly from USB.
HiFi Warm Sound: The 6A2 tube delivers rich, warm, and sweet tones, enhancing your listening experience. Upgradeable to various tubes (6*1N, JAN5725W, 6AK5, EF95) for personalized sound profiles.
Customizable Sound: Independent treble and bass knobs allow precise tone adjustments, while the main volume control ensures seamless output.
User-Friendly Design: Easily switch inputs with the selector and LED indicators – no need to reconnect cables repeatedly.
Premium Build and Aesthetic: CNC-machined black aluminum alloy chassis for durability, complemented by a vintage orange tube glow for a stylish and nostalgic appeal.
Specifications
Audio input
Bluetooth 5.0 / USB (U-Disk) / Stereo RCA
Audio output
Stereo RCA
Maximum capacity U-disk supported
64 GB
Highest sampling rate U-disk supported
24 Bit/192 K (FAT32)
Formats U-disk supported
MP3/APE/FLAC/WAV/WMA
Treble/bass range
±6 dB
Frequency response
20 Hz-20 kHz (±1 dB)
Distortion
≤0.03%
RCA input sensitivity
0 dBFS/1 V
SNR
≥100 dB
Working voltage
DC 12 V
Dimensions
97 x 118 x 33 mm
Weight
337 g
Included
1x Douk Audio P6 mini Tube Preamp
2x 6A2 Tube
1x Bluetooth Antenna
1x Power Adapter (12 V DC)
1x Manual
Programming the Finite State Machine with 8-Bit PICs in Assembly and C
Andrew Pratt provides a detailed introduction to programming PIC microcontrollers, as well as a thorough overview of the Finite State Machine (FSM) approach to programming. Most of the book uses assembly programming, but do not be deterred. The FSM gives a structure to a program, making it easy to plan, write, and modify. The last two chapters introduce programming in C, so you can make a direct comparison between the two techniques. The book references the relevant parts of the Microchip datasheet as familiarity with it is the best way to discover detailed information.
This book is aimed at Microsoft Windows and Linux users. To keep your costs to a minimum and to simplify the toolchain, specific applications are provided as a free download to enable you to use an FTDI serial lead as the programmer. The assembler used is the open-source "gpasm". All programming can be done in a text editor. There are detailed instructions on how to perform the necessary installations on Windows, Linux Debian, and derivatives such as Ubuntu and Fedora. For programming in C, Microchip's XC8 compiler is used from the command line. In addition to the programming applications, two serial read and serial write applications can be used for communicating with the PICs from a computer.
A voltmeter project including practical instructions on building a circuit board from scratch is included. All theory is covered beforehand, including how to do integer arithmetic in assembly.
Two PICs are covered: the PIC12F1822 and the PIC16F1823. Both can run at 32 MHz with an internal oscillator. You do not need to buy a factory-made development board and programmer. With relatively inexpensive parts including a serial lead, microcontroller, a few resistors, and LEDs, you can get started exploring embedded programming.
Links
Updated Programmer
The intention of this book is to offer the reader understandings, ideas and solutions from the perspective of a workbench technician and electronics hobbyist. It is a descriptive text with many tables of useful data, servicing tips and supplementary notes of not so common knowledge.
Today there is a re-emerging, nostalgic interest in vinyl records and associated music entertainment gear. With this interest, there is a paralleled market for the repair of this gear.
This ‘hands-on’ servicing guide opens with fundamental considerations of the work space of repair and servicing. This includes a comprehensive discussion of essential test equipment and tools. Two chapters are devoted to obtaining servicing information about repair and obtaining spare parts. A key chapter is on general diagnosis and testing and includes the discussion of resistance, capacitance and inductance. These electrical properties are regularly in the mind of the repairer, so understanding of them is a key objective of this book. The next chapter is about time saving repair techniques and ensuring quality repair. The remaining chapters discuss entertainment equipment itself. Each of the chapters begins with an orderly discussion of the theory of operation and common and not so common problems specific to the equipment. All chapters conclude with a summary.
Easy and Affordable Digital Signal ProcessingThe aim of this book is to teach the basic principles of Digital Signal Processing (DSP) and to introduce it from a practical point of view using the bare minimum of mathematics. Only the basic level of discrete-time systems theory is given, sufficient to implement DSP applications in real time. The practical implementations are described in real time using the highly popular ESP32 DevKitC microcontroller development board. With the low cost and extremely popular ESP32 microcontroller, you should be able to design elementary DSP projects with sampling frequencies within the audio range. All programming is done using the popular Arduino IDE in conjunction with the C language compiler.After laying a solid foundation of DSP theory and pertinent discussions on the main DSP software tools on the market, the book presents the following audio-based sound and DSP projects:
Using an I²S-based digital microphone to capture audio sound
Using an I²S-based class-D audio amplifier and speaker
Playing MP3 music stored on an SD card through an I²S-based amplifier and speaker
Playing MP3 music files stored in ESP32 flash memory through an I²S-based amplifier and speaker
Mono and stereo Internet radio with I²S-based amplifiers and speakers
Text-to-speech output with an I²S-based amplifier and speaker
Using the volume control in I²S-based amplifier and speaker systems
A speaking event counter with an I²S-based amplifier and speaker
An adjustable sinewave generator with I²S-based amplifier and speaker
Using the Pmod I²S2 24-bit fast ADC/DAC module
Digital low-pass and band-pass real-time FIR filter design with external and internal A/D and D/A conversion
Digital low-pass and band-pass real-time IIR filter design with external and internal A/D and D/A conversion
Fast Fourier Transforms (FFT)
The QA403 is QuantAsylum's fourth-generation audio analyzer. The QA403 extends the functionality of the QA402 with improved noise and distortion performance, in addition to a flatter response at band edges. The compact size of the QA403 means you can take it just about anywhere.
Features
24-bit ADC/DAC
Up to 192 kSPS
Fully isolated from PC
Differential Input/Output
USB powered
Built-in Attenuator
Fast Bootup and Driverless
The QA403 is a driverless USB device, meaning it’s ready as soon as you plug it in. The software is free and it is quick and easy to move the hardware from one machine to the next. So, if you need to head to the factory to troubleshoot a problem or take the QA403 home for a work-from-home day, you can do it without hassle.
No-Cal Design
The QA403 comes with a factory calibration in its flash memory, ensuring consistent unit-to-unit performance. On your manufacturing line you can install another QA403 and be confident what you read on one unit will be very similar to the next unit. It is not expected that re-calibration will be required at regular intervals.
Measurements
Making basic measurements is quick and easy. In a few clicks you will understand the frequency response, THD(+N), gain, SNR and more of your device-under test.
Dynamic Range
The QA403 offers 8 gain ranges on the input (0 to +42 dBV in 6 steps), and 4 gain ranges on the output (-12 to +18 dBV in 10 dB steps). This ensures consistent performance over very wide ranges of input and output levels. The maximum AC input to the QA403 is +32 dBV = 40 Vrms. The maximum DC is ±40 V, and the maximum ACPEAK + DC = ±56 V.
Easy Programmability
The QA403 supports a REST interface, making it easy to automate measurements in just about any language you might anticipate. From Python to C++ to Visual Basic—if you know how to load a web page in your favorite language, you can control the QA403 remotely. Measurements are fast and responsive, usually with dozens of commands being processed per second.
Isolated and USB Powered
The QA403 is isolated from the PC, meaning you are measuring your DUT and not chasing some phantom ground loop. The QA403 is USB powered, like nearly all our instruments. If you are setting up remotely, throw a powered hub in your bag and your entire test setup can be running with a minimum of cables.
Goodbye Soundcard, Hello QA403
Tired of trying to make a soundcard work? The calibration nightmare? The lack of gain stages? The limited drive? Are you tired of dealing with the fixed input ranges? The worry that you might destroy it with too much DC or AC? Tired of the ground loops? That’s why QuantAsylum built the QA403.
Specifications
Dimensions
177 x 44 x 97 mm (W x H x D)
Weight
435 g
Case Material
Powder-coating Aluminum (2 mm thick front panel, 1.6 mm thick top/bottom)
Downloads
Datasheet
Manual
GitHub
SHIM is an old Yorkshire term meaning 'Shove Hardware In Middle' - we use it for Raspberry Pi add-ons that are designed to be sandwiched between your Pi and a HAT or mini HAT. This one has a clever friction fit header that slips handily over your GPIO pins, doesn't need soldering*, and is easily removable. The MAX98357A combined DAC / amplifier chip takes high-quality digital audio from your Pi and amplifies it so it can be used with an unpowered speaker. The push-fit connectors make it straightforward to connect up your speaker, whether it's a bookshelf or floor-standing speaker, the speaker in an old radio, or any other speaker you might have laying around. Because Audio Amp SHIM adds no extra bulk to your Pi it's perfect for building into a compact enclosure - you could use it to make a tiny MP3 player to play local files or stream from services like Spotify, give a vintage radio the ability to play digital radio streams or incorporate bleepy noises into your very own retro handheld. It's also a handy way to add audio output to your Pi Zero or Pi 400! Please note: Raspberry Pi and speakers are not included with this board. Features MAX98357A DAC / amplifier chip Mono 3W audio out Push-fit speaker terminals SHIM-format board with friction-fit connectors 2x mounting holes (M2.5) for if you want to secure everything together with bolts Fully-assembled No soldering required (*unless you're using a Pi that comes without a header) Compatible with all 40-pin header Raspberry Pi models
Software The easiest way to get everything set up is to use Pimoroni's Pirate Audio software and installer which configures I2S audio, as well as installing Mopidy and our custom Pirate Audio plugins which will let you stream Spotify and play local files. Here's how to get started: Set an SD card up with the latest version of Raspberry Pi OS. Connect to Wi-Fi or a wired network. Open a terminal and type the following:git clone https://github.com/pimoroni/pirate-audiocd pirate-audio/mopidysudo ./install.sh
Reboot your Pi Downloads MAX98357A Datasheet Pirate Audio software Schematic
This comprehensive book on audio power amplifier design will appeal to members of the professional audio engineering community as well as the student and enthusiast.
Designing Audio Power Amplifiers begins with power amplifier design basics that a novice can understand and moves all the way through to in-depth design techniques for very sophisticated audiophiles and professional audio power amplifiers.
This book is the single best source of knowledge for anyone who wishes to design audio power amplifiers. It also provides a detailed introduction to nearly all aspects of analog circuit design, making it an effective educational text.
Develop and hone your audio amplifier design skills with in-depth coverage of these and other topics:
Basic and advanced audio power amplifier design
Low-noise amplifier design
Static and dynamic crossover distortion demystified
Understanding negative feedback and the controversy surrounding it
Advanced NFB compensation techniques, including TPC and TMC
Sophisticated DC servo design
MOSFET power amplifiers and error correction
Audio measurements and instrumentation
Overlooked sources of distortion
SPICE simulation for audio amplifiers, including a tutorial on LTspice
SPICE transistor modeling, including the VDMOS model for power MOSFETs
Thermal design and the use of ThermalTrak transistors
Four chapters on class D amplifiers, including measurement techniques
Professional power amplifiers
Switch-mode power supplies (SMPS)