EI66*28 Encapsulated Audio Isolation Transformer - 220 V 50 Hz Primary | 23 V ±5% No-Load Output | H50N EI66 Laminated Core | 60 mm Max Height | Chassis Mount
EI66*28 is an encapsulated audio isolation transformer: 220 V AC 50 Hz primary, 23 V ±5% no-load output, EI66 H50N laminated core, 250 mm silicone leads, panel-mount steel bracket.
- 220 V AC, 50 Hz primary with 23 V ±5% no-load output on the blue-blue winding
- No-load current 55 mA MAX, no-load loss 4.5 W MAX
- AC 1500 V primary-secondary, AC 1000 V winding-to-core dielectric strength; ≥100 MΩ insulation resistance
- EI66 H50N electrical steel core, flame-retardant Nylon 101 bobbin, vacuum varnish impregnated and fully encapsulated
- 250 ±10 mm silicone leads, zinc-plated steel bracket, 60 mm maximum height
ZXY Part No. B2348, specification 20230803003. Tested to EU standards in an ISO 9001 certified factory; CCC, CE, RoHS and UL covered.
1. Product Name
EI66*28 Encapsulated Audio Isolation Transformer. Model / Part No. EI66*28, ZXY Part No. B2348, core size EI66x28, specification 20230803003.
The EI66x28 is a 50 Hz encapsulated audio isolation transformer built on a compact EI66 laminated core. It is wound for a 220 V AC, 50 Hz primary and provides a 23 V ±5% no-load output on the blue-blue winding, with a no-load current of 55 mA MAX and a no-load loss of 4.5 W MAX.
The winding is housed in a flame-retardant nylon bobbin, fully encapsulated and vacuum varnish impregnated, and mounted on a zinc-plated steel bracket for panel installation. In amplifier equipment the transformer isolates the audio signal and power paths, suppressing hum, noise and common-mode interference so that the signal path stays stable and clean.
2. Feature
Reliable encapsulated construction — fully encapsulated winding with vacuum varnish impregnation for moisture resistance and long-term reliability.
Pure copper winding — high-grade pure copper wire for stable, low-loss transmission.
Flame-retardant nylon bobbin — durable insulation with high heat resistance (UL file E41938).
Compact EI66 core — high-permeability H50N electrical steel laminations delivering optimised magnetic flux and low loss.
Insulated lead wires — flexible silicone lead wires, 250 mm ±10 mm, with tinned copper terminations.
Steel mounting bracket — 0.5 mm frame with 0.8 mm bracket for standard panel mounting.
Audio signal isolation — effectively isolates noise and hum for clean audio performance.
Low frequency stability — designed and tested for stable operation at 50 / 60 Hz.
3. Advantage
High common-mode rejection — the isolation barrier separates the audio stage from power and ground noise, removing ground-loop hum.
Enhanced dielectric strength — AC 1500 V primary-secondary and AC 1000 V for primary-core and secondary-core, giving ample safety margin in amplifier power sections.
High insulation resistance — ≥100 MΩ MIN (DC 500 V / 1 min) keeps isolation stable over the product lifetime.
Low no-load current and loss — 55 mA MAX and 4.5 W MAX reduce heat build-up and standby energy consumption.
Stable performance, low noise — consistent electrical output with low audible noise in continuous operation.
Direct factory supply — manufactured in-house by a supplier with 26 years of transformer experience (since 1998), giving competitive pricing and stable lead times.
OEM and custom solutions — custom winding (turns ratio, impedance, inductance), custom dimensions, custom electrical specifications, and support from prototype to mass production.
Custom winding covers turns ratio, impedance and inductance; custom dimensions are matched to the space available; custom electrical specifications cover voltage, frequency and power. Prototype builds are supported through to mass production.
4. Application
The EI66x28 is intended for audio amplifier and low-frequency isolation duty, including:
Audio amplifier and power isolation stages — the transformer sits between the mains side and the audio supply, breaking the ground loop that causes hum.
Public address systems, active speakers and professional audio equipment — line-level and supply isolation in equipment that must stay quiet at low signal levels.
Instrumentation, control panels and measurement equipment — isolating a 50 / 60 Hz supply where a ground loop would otherwise corrupt a measurement.
Isolated 50 / 60 Hz signal and supply interfaces — a compact isolation barrier for interfaces that must not share a common reference.
OEM audio equipment — a fully encapsulated isolating transformer that fits a standard panel cut-out.
5. Application Specifications
Electrical performance. All values as listed in the specification for approval:
| Parameter | Specification | Test Condition |
|---|---|---|
| Rated primary voltage | 220 V AC, 50 Hz | — |
| No-load current | 55 mA MAX | — |
| No-load loss | 4.5 W MAX | — |
| No-load output voltage (blue-blue) | 23 V ±5% | — |
| Dielectric strength PRI-SEC | AC 1500 V | 1 mA, T = 1 s, 50 Hz |
| Dielectric strength PRI-CORE | AC 1000 V | 1 mA, T = 1 s, 50 Hz |
| Dielectric strength SEC-CORE | AC 1000 V | 1 mA, T = 1 s, 50 Hz |
| Insulation resistance PRI-SEC | ≥100 MΩ MIN | DC 500 V / 1 min |
Construction and outline dimensions. All dimensions are in millimetres (mm).
| Item | Specification |
|---|---|
| Core type | EI66 laminated core, H50N electrical steel sheets |
| Maximum height | 60 mm |
| Width | 30.5 mm |
| Bracket thickness | 0.8 mm |
| Frame thickness | 0.5 mm |
| Lead wire length | 250 mm ±10 mm, flexible silicone insulated |
| Encapsulation | Vacuum varnish impregnated, fully encapsulated |
| Mounting | Zinc-plated steel bracket, panel mount |
Material list:
| No. / Description | Specification | UL File No. |
|---|---|---|
| Bobbin | Nylon 101 | E41938 |
| Tape | CT-280 | E165111 |
| Wire | 2UEW-F | E344055 |
| Jumper wire | UL AWG22 | E189674 |
| Core | H50N electrical steel sheets | — |
| Frame | 0.5 mm thickness steel | — |
| Bar tin | Sn-Cu | — |
| Varnish | E962 | E228349 |
6. Quality & Testing Assurance
Every unit is electrically tested before shipment. The inspection items and test conditions are:
HI-POT insulation — PRI-SEC AC 1500 V (1 mA, 50 Hz, 1 s).
Insulation resistance — PRI-SEC ≥100 MΩ (DC 500 V / 1 min).
No-load voltage — 23 V ±5%.
Test condition — 1 mA, T = 1 s, 50 Hz.
The EI66 series is manufactured to meet EU standards in an ISO 9001 certified factory and is CE and RoHS compliant. Certification covered: CCC, CE, RoHS, UL and ISO 9001. Each transformer is identified with its own product label and is packed for safe transport, so that performance is repeatable from the first sample to volume production.