VOOHU product sharing–audio transformer technology white paper
Global application market distribution
• North America: Mainly the United States and Canada, the main demand comes from professional audio equipment and high-end audio markets
• Europe: 德国, the United Kingdom and France are the main markets, and the demand is concentrated in professional audio systems and broadcasting equipment
• Asia-Pacific: The market size is growing rapidly, China and Japan are the main producers and consumer markets, and the demand in India and Southeast Asian countries is also growing rapidly
• Other regions: The markets in South America and the Middle East are relatively small, but the growth potential is large
Growth drivers
1. Growth of the consumer electronics market
• With the popularity of smartphones, tablets and portable audio devices, the demand for audio transformers continues to increase
2. Demand for professional audio equipment
• The demand for high-quality audio transformers in professional fields such as recording studios, theaters, and radio stations continues to grow
3. Technological progress
• The application of new materials (such as nanocrystalline alloys) and new processes has improved the performance and efficiency of audio transformers and promoted market development
4. Emerging application areas
• Emerging fields such as smart homes, car audio, and the Internet of Things provide new market opportunities for audio transformers
Technical Difficulties
one. Frequency Response and Distortion Control
The frequency response and distortion control of audio transformers directly determine the sound quality restoration capability and are the core challenges of audio system design.
1. Analysis of frequency response problems
Low-frequency attenuation (<100Hz):
Reason: Insufficient inductance of primary winding leads to increased magnetizing current of low-frequency signal and close saturation of magnetic core
Solution:
Select high permeability (μ) magnetic core (such as nanocrystalline alloy μ>50,000)
Increase the number of winding turns (N↑ → inductance L↑)
Use layered and segmented winding to reduce leakage inductance
High-frequency attenuation (>10kHz):
Reason: Winding distributed capacitance and leakage inductance form LC resonance, and high-frequency signal is bypassed
Solution:
Honeycomb winding: interlaced winding reduces interlayer capacitance (distributed capacitance can be reduced by 30%-50%)
Core cross-sectional area optimization: reduce magnetic path length to increase cutoff frequency
2. Distortion type and suppression
Harmonic distortion (THD):
Source: core nonlinearity (working in the bending area of B-H curve), DC bias
Countermeasure:
Select high saturation flux density material (such as Sendust ≈ 1.2T)
Add air gap (reduce effective magnetic permeability, expand linear region)
Phase distortion:
Source: Group delay difference caused by winding inductance and distributed capacitance
Countermeasures:
Control the Q value of the winding, usually the target Q value is between 1-3
Use symmetrical dual winding structure (such as bifilar winding) to balance parasitic parameters
3. Actual measurement verification method
Frequency response test:
Use APx555 audio analyzer, input sweep signal (20Hz-100kHz), record attenuation-frequency curve
Qualification standard: Fluctuation within the target frequency band ≤±1dB (Hi-Fi level requirement)
Distortion test:
Input 1kHz sine wave, measure THD+N (total harmonic distortion + noise) at rated power
Typical value: consumer level <1%, Hi-Fi level <0.1%
two. Impedance matching accuracy
Impedance matching error exceeding ±10% will cause signal reflection (standing wave ratio VSWR>1.22), seriously affecting transmission efficiency
1. Impedance matching principle
Ideal matching conditions:
(source impedance), (load impedance)
Transformer turns ratio: (primary impedance, secondary impedance)
Actual deviation factors:
Winding resistance consumes signal power
Leakage inductance forms inductive reactance at high frequencies
2. Matching design strategy
Low-frequency matching (<1kHz):
Prioritize accurate turns ratio and select low-loss copper wire (such as OFC oxygen-free copper)
Example: Matching 600Ω microphone output to 10kΩ preamplifier input requires turns ratio
High-frequency matching (>10kHz):
Need to compensate for parasitic parameters, and capacitors can be connected in parallel to offset leakage inductance
3. Debugging and verification
Network analyzer method:
Measure S parameters (S11/S21), adjust the turns ratio to make S11<-20dB (reflected power <1%)
Actual load test:
Connect the real load (such as power amplifier + speaker) and use an oscilloscope to observe whether the signal waveform is distorted
three. Electromagnetic Interference (EMI) Suppression
EMI can introduce audible noise (such as “buzzing”), which may cause equipment malfunction in medical and industrial scenarios
1. Analysis of EMI sources
Conducted interference:
High-frequency switching power supply noise is coupled through the power line (frequency band: 150kHz-30MHz)
Radiated interference:
Transformer leakage magnetic field forms an alternating magnetic field in space
2. Suppression technology solution
Magnetic shielding:
Three-layer shielding structure:
Inner layer: copper foil (≥0.1mm) shields the electric field
Middle layer: high magnetic permeability alloy (such as Mu-metal) guides leakage magnetic field
Outer layer: ferrite magnetic ring absorbs residual high-frequency noise
Winding optimization:
Dual-wire parallel winding: The magnetic fields generated by the primary and secondary currents cancel each other, and the common mode rejection ratio (CMRR) is increased to more than 60dB
Electrostatic shielding layer: Insert copper foil between the primary and secondary and single-point grounding can reduce distributed capacitance coupling noise by 50%-70%
3. Key test standards
CISPR 32 radiated emission test
Measured in the 30MHz-1GHz frequency band in an anechoic chamber, it must be below the limit line (such as Class B equipment ≤40dB
μV/m)
IEC 61000-4-6 conducted immunity:
Injected with a 150kHz-80MHz interference signal, the device output signal-to-noise ratio (SNR) must drop by <3dB
Main parameters of audio transformer
1. Power Rating/Watt (瓦)
• Meaning: The maximum power that an audio transformer can safely transmit. Exceeding the rated power may cause the transformer to overheat, damage, or distort. 例如, an audio transformer with a rated power of 100W is suitable for audio equipment with a maximum output power of 100W.
2. Frequency Response/Hertz (Hz) or decibel (dB)
• Meaning: Indicates the ability of an audio transformer to transmit signals at different frequencies. It is usually expressed in terms of frequency range (such as 20Hz to 20kHz) and corresponding insertion loss (such as ±3dB). 例如, a transformer with a frequency response of 20Hz to 20kHz±1dB can maintain high-fidelity transmission of signals within this frequency range.
3. Impedance Ratio/Ohm (Ω)
• Meaning: The ratio of the impedance at the input and output ends of an audio transformer. 例如, a transformer with an impedance ratio of 600Ω:150Ω can convert a 600Ω source impedance into a 150Ω load impedance, thereby achieving impedance matching and reducing signal reflection and distortion.
4. Turns Ratio/None (usually expressed as a ratio, such as 1:1, 2:1)
• Meaning: The ratio of the number of turns of the primary coil to the number of turns of the secondary coil. This parameter determines the relationship between the input voltage and the output voltage. 例如, a 1:2 transformation ratio means that the output voltage is twice the input voltage.
5. Insertion Loss/dB
• Meaning: Indicates the energy loss when the audio signal passes through the transformer. The smaller the insertion loss, the higher the signal transmission efficiency. 例如, a transformer with an insertion loss of 0.5dB means that the energy loss when the signal passes is small.
6. Isolation Voltage/Volt (V)
• Meaning: The electrical isolation capability between the input and output ends. A higher isolation voltage can effectively prevent ground noise and power supply interference. 例如, a transformer with an isolation voltage of 1000V can provide good electrical isolation.
7. DC Resistance (DCR) / Ohm (Ω)
• Meaning: The DC resistance of the coil affects the efficiency and heat generation of the transformer. Lower DC resistance can reduce energy loss and heat generation. 例如, a transformer with a primary DC resistance of 10Ω generates less heat when transmitting large currents.
8. Operating Temperature Range (Operating Temperature Range) / ℃
• Meaning: The temperature range in which an audio transformer can operate normally. 例如, a transformer with an operating temperature range of -20°C to +85°C is suitable for a variety of environmental conditions.
9. Insertion Loss (Insertion Loss) / decibel (dB)
• Meaning: The energy loss of the signal when it passes through the transformer. The smaller the insertion loss, the higher the signal transmission efficiency. 例如, a transformer with an insertion loss of 0.5dB means that the energy loss is small when the signal passes through.
10. Dimensions/mm or in
• Meaning: The physical dimensions of the audio transformer, including width, depth and height. The dimensions determine how the transformer is mounted and the type of equipment it is suitable for.
11. Conventional model display
Introduction and application fields of audio transformers
1. Consumer electronics
• Portable audio devices: used for impedance matching and signal isolation to ensure clear transmission of audio signals
• Home audio systems: used to improve sound quality, reduce noise interference, and achieve high-quality audio output
• Headphone amplifiers: used to match the impedance of headphones to improve the transmission efficiency and sound quality of audio signals
2. Professional audio equipment
• Mixing consoles: used for signal isolation and impedance matching to ensure that signals from different audio sources can be transmitted stably and do not interfere with each other
• Recording studio equipment: used to isolate noise and improve signal purity and fidelity
• Stage sound systems: used for signal transmission between power amplifiers and speakers to ensure stable transmission and high-quality output of high-power audio signals
• Effectors: used for processing and transmission of audio signals to ensure that signals are not distorted during processing
3. Automotive electronics
• Automotive audio systems: used for impedance matching and signal isolation to ensure stable transmission of audio signals in complex automotive electrical environments and improve in-car sound quality
• In-car entertainment systems: used for transmission and processing of audio signals to ensure high-quality audio experience
4. Broadcasting and Communication
• Radio stations: used for signal transmission and isolation in broadcasting equipment to ensure high-quality transmission of broadcast signals
• Communication equipment: used for isolation and transmission of audio signals to reduce electromagnetic interference
5. Smart Home
• Smart speakers: used for impedance matching and signal isolation to ensure high-quality transmission of audio signals
• Smart audio equipment: used to improve signal quality and anti-interference ability
6. Industry and Medical
• Industrial audio system: used for signal isolation and transmission to ensure the stability and reliability of audio signals in industrial environments
• Medical equipment: used to isolate noise and ensure clear transmission of audio signals
7. Musical instruments and music production
• Electronic musical instruments: used for transmission and processing of audio signals to improve sound quality
• Music production equipment: used for signal isolation and impedance matching to ensure high-quality processing of audio signals
8. Education and Public Broadcasting
• Educational equipment: used to improve the quality and transmission efficiency of audio signals
• Public Broadcasting System: used for signal isolation and transmission to ensure the clarity and stability of audio signals
