Audio Applications · Protech Engineering

For twenty years we have been designing and building electronics for audio signal processing and amplification, in both analog and digital technology, with the utmost attention to sound fidelity. We support our customers in designing and developing innovative, technologically advanced products:

Class AB audio amplifiers
Class D switching power amplifiers
Crossover filters for loudspeakers
Switching power supplies and PFC for power amplification systems
Analog audio processing systems: preamplifiers, filters, mixers, equalizers, compressors
Digital audio signal processing (DSP) systems: FIR and IIR filters, compressors, limiters, digital audio effects
Protocols and systems for transmitting audio streams over communication networks (Audio Over Ethernet)
Wireless audio: WiFi, Bluetooth or proprietary systems

The audio design activities described on this page are carried out by Audio Electrons, Protech's internal division dedicated to audio electronics. You can visit the Audio Electrons website at www.audioelectrons.com.

Power audio amplification

Audio amplification, in the broadest sense of the term, has very wide-ranging fields of application and comes in the most diverse shapes and sizes. Consider that it is used in everything from battery-powered mobile devices (MP3 players, smartphones, etc.), where the signal doesn't exceed fractions of a watt, up to very complex and articulated multichannel amplification systems with several thousand watts of output.

The technologies used are also highly varied depending on the context of use. The typical Class AB analog amplifier has, over the years, reached a very high degree of sound quality, but suffers from poor energy efficiency and therefore does not allow for very aggressive size-oriented industrialization.

On the other hand, the switching technology offered by Class D is now very mature and makes it possible to achieve very high efficiencies, which are mainly necessary in very high power applications (several kW), while still maintaining a sound quality level only slightly lower than the analog alternative.

Over the years, the Protech team has developed, for its customers, various types and sizes of audio amplifiers, all characterized by particular attention to technical and sound quality, industrialization, and performance.

100W Class AB MOSFET acoustic guitar amplifier, complete with low-noise microphone preamp stage, tone controls, effects (reverb, chorus and flanger) and Bluetooth receiver.

60W discrete High-End Class AB BJT amplifier, complete with thermal, overcurrent, undervoltage and DC offset protection circuits; industrialized module with surface-mount components.

Compact multichannel Class D amplifier, 2x30W + 1x50W, featuring a line input and an A2DP Bluetooth receiver. Compatible with Google Chromecast and Amazon Alexa.

Medium power Class D amplifier, 2x250W / 1x400W in bridge configuration, with dedicated AC/DC or DC/DC switching power supply.

High power Class D amplifier, 2x700W / 1x1400W in bridge configuration, with integrated DSP module and sinusoidal input (PFC) switching power supply.

Passive crossover filters

We design and build custom crossover networks for loudspeakers, tailored to customer requirements.

Two-way or three-way crossover networks
Audio power up to 1500W
Linkwitz-Riley and Butterworth topologies

Analog audio processing

In the audio field, analog processing of very small signals (down to the microvolt level) requires unconventional expertise and sensitivity, usually not needed in many other fields of electronics, which our hardware design team possesses. Typical applications include:

Low-noise signal conditioning and preamplification circuits
Mixing stages (audio mixers)
Analog filters and equalizers
Microphone preamplifiers
VCAs, compressors and limiters
Low-noise power supply systems

Audio and DSP (Digital Signal Processors)

The widespread availability of very high performance DSPs (Digital Signal Processors) at extremely low prices has opened up new horizons in all applications requiring complex real-time audio processing. At Protech, in addition to the classic DSPs from Analog Devices and TI, we use the new ARM CORTEX M4/M7 cores (with integrated FPU, single-core and dual-core) for real-time digital audio processing applications, with extremely interesting results.

Some of our implementations:

FIR and IIR digital filtering algorithms, equalization and parametric tone controls
Digital audio effects: delay, echo, chorus, flanger, reverb
Active crossover filters: Butterworth and Linkwitz-Riley
FFT applications, fast convolution, frequency-domain filtering
Digital compression, limiting and gain control techniques
Sound spatialization algorithms
Sound intensity measurement techniques, RMS and Leq calculation with A and C weighting curves, third-octave analysis

Long-distance transmission of digital audio signals

Several technologies today enable the transmission of audio signals without wires. The Bluetooth standard allows audio tracks to be transferred from mobile devices, such as smartphones and music players, to the amplification/playback system, typically over fairly limited distances. WiFi connectivity, on the other hand, allows audio streams to be propagated over wireless networks and existing infrastructure, even over a wider range.

Other proprietary technologies allow wireless audio transmission (usually on the 2.4GHz ISM band) with the desired characteristics in terms of range or network extension, topology (point-to-point/multipoint, unicast/multicast or broadcast), always with high quality and minimal latency.

Finally, there are various standard protocols that allow the transmission of digital audio signals over wired communication networks based on TCP/IP infrastructure.

Protech is able to design communication boards with DSP processors or Embedded Linux platforms suited to implementing audio streaming protocols over wired (Audio Over LAN) or wireless (Bluetooth, WiFi, 2.4GHz, UWB) networks.

Electronic design for audio applications

Power audio amplification

Passive crossover filters

Analog audio processing

Audio and DSP (Digital Signal Processors)

Long-distance transmission of digital audio signals

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