EE25-4.0H 1:1:1:1 Audio Isolation Transformer - Four Matched 4.0 H Windings | 20 Hz to 20 kHz | DIP Through-Hole | PCB Mount

1. Product Overview

The EE25-4.0H is a PCB-mountable audio isolation transformer built on the EE25 in-line bobbin platform. With a 1:1:1:1 turns ratio and four matched 4.0 H windings, this device provides galvanic isolation between circuits, suppresses AC hum caused by system grounds, and enables clean coupling of balanced or unbalanced audio signals from 20 Hz to 20 kHz. It is used for voice and data coupling, breaking ground loops between devices, and providing isolated signal outputs.

Figure 1 — EE25-4.0H audio isolation transformer in DIP through-hole in-line package.

Basic Information

Item	Specification
Model / Part Number	EE25-4.0H
Transformer Type	Audio Isolation / Coupling Transformer
Frequency Range	20 Hz – 20 kHz
Package	DIP Through-Hole, In-Line
Test Conditions	25 °C
Customization	Turns ratio, inductance, and pin configuration can be customized upon request

2. Product Features

• Galvanic Isolation — Protects the output of upstream equipment from damage.
• Voice and Data Coupling — Coupling transformer for voice and data lines.
• Frequency Range — 20 Hz to 20 kHz.
• Ground Loop Hum — Resolves AC hum issues caused by system grounding.
• Interference Suppression — Reduces external interference in both balanced and unbalanced transmission.
• Four Matched Windings — 1:1:1:1 turns ratio, brought out to pins 1-2, 3-4, 5-6, and 7-8 respectively.
• PCB Mount — DIP through-hole package for direct PCB mounting.

Figure 2 — Winding and insulation details.

3. Product Advantages

• Cost-Effective — High cost-performance in mass production.
• Standard Package Size — DIP through-hole package compatible with standard PCB layouts and conventional wave or selective soldering.
• Customizable — Custom designs available for specific turns ratios, inductance values, or pin arrangements.
• Factory Direct — In-stock inventory for immediate shipment.
• Versatile — A single matched four-winding device meets multiple audio coupling and isolation requirements.

4. Applications

• Communication Equipment — Isolation of line and voice interfaces, inter-stage coupling.
• Automotive Audio — Breaking ground loops between head units, amplifiers, and speakers.
• Telephone and Fax — Voice-band coupling and line isolation.
• Isolated Signal Output — Isolating outputs before long-distance cable transmission.

In each application, the transformer sits in the signal path, isolating the two sides of the circuit from each other. Direct ground connections are removed, DC bias cannot pass through, and interference picked up on cables is attenuated without being superimposed on the desired signal.

5. Technical Specifications

The following values are specifications for the EE25-4.0H. Electrical parameters are measured at 25 °C.

5.1 Electrical Specifications (25 °C)

Parameter	Test Conditions	Specification
Turns Ratio	–	1:1:1:1
Inductance L(1-2)	1 kHz, 0.3 V, min	4.0 H
Inductance L(3-4)	1 kHz, 0.3 V, min	4.0 H
Inductance L(5-6)	1 kHz, 0.3 V, min	4.0 H
Inductance L(7-8)	1 kHz, 0.3 V, min	4.0 H
Dielectric Withstanding Voltage	1 mA, 60 s	1000 V

Inductance is the minimum value at the specified test frequency and level for each winding.

5.2 Dimensions (Unit: mm)

Dimension	Value
Overall Width, Front View	25.5 mm
Overall Height, Front View	22.0 mm
Overall Depth, Side View	18.5 mm
Pin Area Depth, Bottom View	12.5 mm
Pin Pitch	5 mm

Winding 1 is brought out to pins 1-2, winding 2 to pins 3-4, winding 3 to pins 5-6, and winding 4 to pins 7-8. The polarity of each winding is indicated on the schematic, and the four windings are matched, so any winding can be used as the primary or secondary side as required by the circuit.

Figure 3 — Front, side, top, and bottom views of the in-line package.

Figure 4 — In-line pin arrangement and solder termination details.

6. Quality and Test Assurance

• Electrical Inspection — Each transformer is inspected against electrical specifications before packaging: turns ratio and inductance of all four windings at 1 kHz and 0.3 V.
• Dielectric Test — Withstanding voltage tested at 1000 V with leakage current limited to 1 mA for 60 seconds.
• Test Conditions — All tests are performed at 25 °C.
• Packaging — Supplied in DIP through-hole in-line package for direct through-hole mounting.