The toroidal transformer guide
Everything worth knowing about toroidal transformers.
Practical, plain-English guides for amplifier builders, engineers and buyers. Learn how toroids work, how to choose the right one, and how to install it so it runs cool and silent.
Start with the basics Browse all guides- ~50%lighter than an equivalent EI transformer
- ~1/10of the stray magnetic field
- 90–98%typical efficiency
- 230 V · 50 Hzdesigned for Indian mains
Guides
Read them in order for the full picture, or jump to what you need.
What Is a Toroidal Transformer?
How a toroidal transformer is built, how it works, and why its ring-shaped core makes it smaller, quieter and more efficient than a conventional transformer.
02Toroidal vs EI Transformers: Which Do You Need?
A practical side-by-side comparison of toroidal and EI laminated transformers: size, weight, hum, stray field, efficiency, inrush current and cost.
03Choosing a Toroidal Transformer for an Audio Amplifier
How to pick the right secondary voltage and VA rating for a Class AB amplifier, with DC rail tables for 24-0-24, 30-0-30 and 50-0-50 toroidal transformers.
04Inrush Current, Fuses and Soft-Start for Toroidal Transformers
Why toroidal transformers draw a large current surge at switch-on, how to choose a slow-blow fuse, and when to add an NTC thermistor or relay soft-start.
05Mounting a Toroidal Transformer (and Fixing Hum)
How to mount a toroidal transformer correctly, avoid the shorted-turn trap, position it for minimum hum, and troubleshoot a buzzing toroid.
06How to Specify a Custom Toroidal Transformer
A checklist of everything a manufacturer needs to quote and build a custom toroidal transformer: voltages, VA, size, mounting, shielding, insulation class and testing.
Need a transformer, not just the theory?
This site is the information side of Vaani, which has been winding 100% copper toroidal transformers in India since 2014. Standard ratings and custom builds are at toroidaltransformer.in.