High-frequency behaviour
High-Frequency Propagation
How high-frequency energy behaves on cables and PCB tracks, and why wavelength, return paths and skin effect matter in audio systems.
Explore High-Frequency PropagationTHE PHYSICS OF QUIET / 07
Understanding Balanced Mains
Why electrical symmetry around earth matters — and why it is only the beginning of controlling high-frequency energy in an audio system.
A centre-tapped balanced transformer can present an audio system with two supply conductors that are equal and opposite relative to Protective Earth, while retaining the full 230 V differential supply between them.
Supply symmetry can reduce conversion of common-mode disturbance into differential error within connected equipment. Quiescent builds on this foundation by controlling the high-frequency paths through earth, chassis and the transformer environment.
Symmetry around earth
In an ordinary supply, one conductor sits close to earth while the other carries the full supply voltage relative to it. A balanced transformer changes that geometry. Its centre-tapped secondary establishes two equal and opposite rails: approximately +115 V and −115 V with respect to Protective Earth, while the equipment still receives 230 V between the rails.
This matters because unwanted energy is often shared by both supply conductors relative to earth or chassis. When the supply is more symmetrical, there is less opportunity for that common-mode energy to be converted into a differential disturbance at an audio component’s power-supply input.
Illustrative principle
Supply energy
Common-mode noise
How to read the illustration
- Follow the blue arrows. They show the differential supply retained through the transformer.
- Follow the green marks on both incoming conductors. They represent common-mode noise: energy related to the conductors’ shared relationship with earth.
- Notice the centre tap leaving the secondary winding for Protective Earth. It establishes a reference and provides a path for some common-mode energy.
- Notice the faint green path that remains across the transformer. It represents residual high-frequency coupling, not a measured product response.
Mains behaviour changes with the music
An audio system does not draw power as a perfectly steady load. As programme material becomes louder or more complex, its power supply asks for current in changing bursts. The transformer, the supply conductors, chassis and earth structure respond to that changing demand as a connected system.
Changing current demand alters conditions across the supply network. Quiescent investigates these interactions as part of the connected system: how programme-related demand affects the transformer, supply, chassis and earth environment while the equipment processes music.
Illustrative relationship between programme demand and disturbance around the transformer, supply, chassis and earth. The traces explain the relationship rather than the measured levels.
How to read the demand illustration
- Read the image from left to right. The four bands describe a quieter passage, rising demand, a more demanding passage and a settling passage.
- The green trace represents changing programme demand: the varying current requests an audio system can make as the music changes. It is not a wattage scale or an audio-level meter.
- The three blue traces represent a changing disturbance environment around the transformer, supply, chassis and earth. They do not identify individual noise sources, frequencies or measured amounts.
- Where the green trace becomes more active, the blue traces become more active too. The illustration links changing demand with changing operating conditions; their relative levels depend on the system. A quieter musical passage does not mean unwanted energy is absent.
Earth is a path, not a sink
The centre tap gives common-mode energy a route towards Protective Earth. That route is useful: it establishes the balanced reference and can carry some unwanted energy away from the two supply conductors. But at high frequencies, Protective Earth is not an ideal, zero-impedance destination.
Earth conductors, chassis bonds and connected ground structures behave as transmission paths at HF. Where a path changes impedance, branches, or ends without enough loss, part of the incident energy can be returned into the shared earth and chassis environment. In an audio system, that returning energy can remain available to interact with component references and signal-bearing circuitry.
Quiescent therefore keeps Protective Earth intact as the safety reference, while using Matrix absorption on the earth plane to provide a more controlled, less reflective destination for unwanted high-frequency energy. The aim is not simply to move HF noise into earth, but to reduce its ability to circulate through the common earth structure.
A second path crosses the transformer
A transformer provides valuable isolation, but no physical transformer is ideal at every frequency. The primary and secondary windings are separated by insulation, geometry and often screening; they also form small parasitic capacitances. At mains frequency, those capacitances may be of little consequence. At higher frequencies, they can become a path for common-mode energy to couple across the isolation boundary.
Parasitic coupling is part of a practical transformer’s high-frequency behaviour. Quiescent uses Matrix absorption around the transformer and its associated earth and chassis paths to control residual energy reaching the secondary-side environment.
Lower primary-to-secondary capacitance and better damping reduce high-frequency transfer. Higher capacitance or a more reflective surrounding environment allows more energy to remain coupled across the boundary. The graphic illustrates high-frequency behaviour, not a specification for a particular transformer.
A path is not the whole picture
This graph illustrates the transformer’s transfer behaviour. The disturbance reaching the secondary depends on both that transfer behaviour and the high-frequency energy present at the primary.
The next view changes perspective. It shows the mixture of energy that can be present on Protective Earth: supply-frequency components, harmonics, switching-related clusters and wider RF activity. Together, the two views explain why Protective Earth is a path to understand, not simply a silent endpoint.
At lower frequencies, Protective Earth behaves as a low-impedance return path and harmonic voltage is held close to the reference. As the quarter wavelength approaches the length of a relevant cable, chassis or earth path, that route must be treated as a transmission structure. A short circuit at its far end is then reflective to a travelling wave, allowing high-frequency energy to return into the audio-system environment.
Where Quiescent extends balanced mains
Balanced mains remains the foundation: isolation and symmetry make the relationship between supply, chassis and earth more controlled. The next question is what happens to the high-frequency energy that still follows the earth route or crosses the transformer through parasitic coupling.
If that energy is only blocked or redirected, it can meet another discontinuity and continue to reflect through the shared earth, chassis and supply environment. Quiescent adds deliberately controlled paths and Matrix absorption so that residual energy has a less disruptive destination.
Matrix absorption on the earth plane addresses the common-earth route. Matrix absorption around the transformer’s primary and secondary environment addresses energy that couples across the winding boundary. Together, these measures extend balanced mains from a useful transformer topology into a broader approach to unwanted energy within the audio system.
1. Symmetry
A centre-tapped transformer retains the differential supply while making the two rails equal and opposite relative to Protective Earth.
2. Earth-plane absorption
Protective Earth remains the safety reference. Matrix absorption helps reduce the opportunity for HF energy to remain active or return through the common earth structure.
3. Secondary-side absorption
Matrix absorption around the transformer environment addresses residual high-frequency energy that can couple across the winding boundary.
Balanced mains establishes a symmetrical supply reference. Quiescent extends that foundation by managing the remaining high-frequency routes through Protective Earth, parasitic winding capacitance and the surrounding transformer environment.
During our development and listening evaluations, reducing unwanted disturbance has repeatedly produced a clearer, more stable musical presentation.
These observations inform our systems approach to mains control. The relevant paths and the extent of the improvement depend on the connected equipment, supply conditions and installation.
Protective Earth must always be retained, and any mains product must be designed, installed and used in accordance with applicable local safety requirements. This page explains a systems principle; it is not a guide to altering mains wiring.
Explore further
System application
Subsystem Protection
How two Matrix boundaries can define a quieter environment around a sensitive part of a system.
Explore Audio Subsystem ProtectionSystem application
Audio Mains Control
Explore Quiescent’s approach to managing unwanted high-frequency energy across an audio system’s mains and earth environment.
Explore Audio Mains ControlTechnical notes
The diagrams illustrate supply symmetry, parasitic coupling and high-frequency return paths. They are conceptual explanations rather than measured product responses. Practical assessment considers transformer construction, connected impedances, disturbance spectrum and the installation’s supply, chassis and earth paths.
The references explain the underlying principles. Quiescent’s own research and development informs their application to working audio systems.
- Sound On Sound — Identifying & Solving Mains Supply Problems. Useful audio-focused background on mains-borne problems, isolation and common-mode leakage.
- Texas Instruments — transformer parasitic-capacitance technical note. Background on how parasitic capacitance can transfer common-mode energy across an isolation boundary at high frequency.
