![Audio Transformers for Car Amplifiers: THD Reduced from 0.8% to 0.15%](["https://zxycoil.oss-cn-beijing.aliyuncs.com/upload/products/zxydu19-permalloy-audio-isolation-transformer-1-1-1-1-turns-ratio-10-h-1.jpg"])
Background
A South China car audio solution provider supplies 4×65W Class-D amplifier modules to an OEM. The original transformer caused high THD at full output and low-frequency distortion at -40°C cold start due to core saturation.
Challenges
- Fit the existing PCB layout with height under 24mm.
- Stable magnetic performance from -40°C to +105°C.
- Withstand 1500V hi-pot and automotive vibration / thermal cycling.
- Eight weeks from design freeze to mass production.
Our Solution
We replaced the original silicon steel core with high-permeability permalloy, redesigned the turns ratio and interlayer structure, and switched to high-temperature resin for vacuum impregnation.
- Turns ratio re-balanced to the amplifier gain curve with 30% flux margin at low frequency.
- Sectional winding with double insulation tape reduced interlayer capacitance by about 25%.
- Grounded metal shield suppresses switching noise coupling.
Results
- THD at full power reduced from 0.8% to below 0.15%.
- No saturation at -40°C cold start; inductance drift under 3% after 500 thermal cycles.
- All units passed 1500V/1min hi-pot; 80,000 pcs delivered with defect rate below 0.3‰.