Zero Feedback Power Amplifiers (Open-Loop Amplifiers)
Zero feedback power amplifiers—also known as open-loop amplifiers—are audio amplifiers that operate without negative feedback. While this design can introduce more distortion on paper, it's often favored by audiophiles for its distinctive sonic character, which many describe as more natural, detailed, and emotionally engaging.
What Is Negative Feedback?
In audio amplifier design, negative feedback is a control technique where a portion of the output signal is inverted and fed back to the input. This loop reduces gain errors, minimizes distortion, and flattens frequency response. Technically, it improves the amplifier’s stability and linearity.
Why Use Zero Feedback?
Despite its technical advantages, some designers and listeners argue that negative feedback dulls the musicality of an amplifier. They claim it can create a sterile or overly processed sound, stripping the audio of its natural dynamics and tonal nuance.
Benefits of Zero Feedback
- Potentially more natural sound: Without the corrective loop of negative feedback, some listeners find the resulting sound more transparent, dynamic, and true to the source material.
- Simplified circuit design: Zero feedback amplifiers typically require fewer components, which can reduce complexity and the potential for introducing signal-altering artifacts such as phase shift or transient smearing.
Drawbacks of Zero Feedback
- Higher distortion: Without feedback to correct non-linearities, distortion is generally higher—especially in traditional silicon-based designs.
- Less consistent frequency response: These amplifiers can exhibit more variation across the audible spectrum, potentially requiring more careful speaker matching.
- Demanding design requirements: To achieve high performance without feedback, circuit layout, component selection, and power supply design must be executed with great precision.
Why Zero Feedback Makes More Sense with GaN Output Devices
When using Gallium Nitride (GaN) transistors, the argument for a zero feedback (open-loop) design becomes significantly stronger.
GaN is a breakthrough material in power electronics. Compared to traditional silicon transistors, GaN FETs switch faster, exhibit far less overshoot and ringing, and introduce much less distortion from the outset. These improvements reduce many of the problems that negative feedback is typically used to correct.
In other words, GaN does less harm to the music in the first place, making it not only feasible but advantageous to eliminate the feedback loop. This allows designers to focus on preserving the purity of the audio signal rather than correcting the flaws of slower, noisier silicon components. The result: an amplifier with excellent sonic performance that stays truer to the input signal—without needing the crutch of feedback.
While we do not claim that our GaN amplifiers sound like tube amplifiers, they do share some of the sonic qualities that tube enthusiasts often praise—such as a warm, musical midrange and open, airy highs. These traits contribute to a rich and engaging listening experience that feels natural and emotionally involving.
However, GaN amplifiers offer significant advantages over traditional tube designs, particularly in two critical areas:
- Low-frequency performance: GaN amplifiers deliver deeper, tighter, and more controlled bass, thanks to their extremely fast switching speeds and lower output impedance. This results in bass reproduction that’s more impactful and better defined, even at high volume levels.
- Power and dynamics: Unlike tube amps, which are typically limited in output power and can struggle with dynamic headroom, GaN amplifiers offer substantially higher output capabilities. This allows them to handle complex musical passages with ease, preserving transient detail and maintaining composure during demanding crescendos or bass-heavy material.
In short, while GaN amplifiers retain some of the musicality and refinement commonly associated with tube gear, they also bring modern performance advantages—delivering a sound that’s not only natural and expressive, but also more dynamic, extended, and precise across the entire frequency spectrum.