Lundahl LL1540 High Impedance Line Input Transformer

Highlights of the Lundahl LL1540

• High impedance, high level line input transformer
• 1 + 1 : 1 + 1 turns ratio for flexible series-series use
• Mu-metal core and mu-metal can for effective shielding
• Electrostatic shield between each primary and secondary section
• 5 Hz to 50 kHz frequency response, ±0.2 dB with 600 Ω source and 15 kΩ load
• 4 kV isolation between windings and 2 kV between windings and shield

Product details Lundahl LL1540

Lundahl LL1540 High Impedance Line Input Transformer

The Lundahl LL1540 is built for high impedance line input applications where clean signal transfer and robust isolation are required. As one of the precision audio components in a signal chain, it uses two coils, each with one primary and one secondary part, separated by an electrostatic shield.

Its high permeability mu-metal core is housed in a mu-metal can, supporting low-noise performance in sensitive audio circuitry. The transformer is normally used in a series-series connection and provides a 1 + 1 : 1 + 1 turns ratio.

For input stage design, the LL1540 supports both symmetric and asymmetric input amplifier connections. In a symmetric amplifier input, the connection is recommended for very high CMRR, while asymmetric input use requires 2 x 12 kΩ resistors for more than 60 dB CMRR.

Performance specifications include a frequency response of 5 Hz to 50 kHz within ±0.2 dB with a 600 Ω source and 15 kΩ load, 0.5 dB loss at 1 kHz with the specified termination and a self-resonance point above 60 kHz. The LL1540 measures 38 x 24 x 17 mm above the PCB, weighs 47 g and uses a recommended PCB hole diameter of 1.5 mm.