INTRODUCTION
Traditionally, audio power amplifiers and preamplifiers follow a classic design based on a differential input stage and voltage feedback.
This approach typically uses a low amount of feedback to preserve sound quality. However, due to the high input impedance and significant input capacitance of differential stages, both bandwidth and slew rate are inherently limited.
Natural and instrumental sounds can range from delicate and detailed to sudden and intense—think of the rapid burst of a thunderclap. With this in mind, we took a different path in developing our audio gain module.
Our proprietary gain module is based on a current feedback architecture. Unlike conventional voltage feedback designs, current feedback features one high-impedance input (for the input signal) and one very low-impedance input (typically 5–10 ohms).
The input stage is built around a unity-gain buffer (B1). The buffer’s low-impedance output feeds the feedback loop. A transimpedance stage (RT) processes the difference between the buffer output and the feedback signal, converting the resulting current into a voltage.
For instance, when the input voltage Vi at the non-inverting terminal increases, the inverting input tracks this change. The resulting current from buffer B1 flows through RG. This current is then amplified by the transimpedance stage, producing a corresponding increase in output voltage—until the current through RF (from output buffer B2) matches the current through RG.
This innovative design enables faster response times, extended bandwidth, and improved detail resolution—delivering a more lifelike and dynamic audio experience.
Dotten line represents bandwidth of a voltage feedback with a gain bandwidth product of 1MHz.
GAIN BANDWIDTH PRODUCT
In voltage feedback amplifiers, increasing the gain typically results in a reduction of bandwidth.
This limitation is known as the Gain-Bandwidth Product—a fundamental characteristic of traditional voltage feedback designs.
In contrast, current feedback amplifiers maintain a relatively constant bandwidth regardless of gain settings. This makes them highly advantageous for audio applications where both high gain and wide bandwidth are desired. Picture illustrates the bandwidth performance at various gain levels.
THE FLS20 VIBRATION CONTROL
Vibrations are the greatest enemy of disc players, and achieving top-tier sonic performance is impossible without total control over drive-induced resonance.
To address this, we developed a unique and highly effective damping system.
At the core of this design is a heavy metal mass, suspended on four custom Sorbothane pads, which isolate and absorb unwanted vibrations. In addition, special attention has been given to the pickup mechanism, which is carefully damped using precision-placed high-performance materials.
This solution was perfected through an extensive series of accelerometer-based measurements, ensuring optimal vibration control and the highest possible sound fidelity.
Vibration spectra of the same drive mechanism in original setup (red) and with the Audia damping system (green).