Lundahl LL1538 Microphone Input Transformer

Highlights of the Lundahl LL1538

• High-permeability mu-metal core with mu-metal case for magnetic shielding
• Two three-section coils for very low leakage inductance and excellent frequency response
• Primary and secondary windings separated by electrostatic shields
• 1 + 1 : 5 turns ratio for microphone input applications
• 10 Hz to 100 kHz frequency response, ±0.3 dB with 200 Ω source and no termination
• No termination required for best square-wave response in 1:5 connection

Product details Lundahl LL1538

Lundahl LL1538 1 + 1 : 5 Microphone Input Transformer

The Lundahl LL1538 is built as a precision audio component for balanced microphone input stages. Its high-permeability mu-metal core and encapsulated mu-metal case help provide magnetic shielding, while the separated primary and secondary windings include electrostatic shields for clean signal transfer.

The transformer uses two three-section coils, a winding structure that keeps leakage inductance very low. This supports a wide frequency response of 10 Hz to 100 kHz within ±0.3 dB when used with a 200 Ω source and no termination. The self-resonance point is above 120 kHz, and no termination is needed for best square-wave response in the 1:5 connection.

Key electric measurements include a static resistance of 44 Ω for each primary winding and 880 Ω for each secondary winding. With the primaries connected in parallel and a 200 Ω source impedance, distortion is 0.2% at 0 dBU primary level at 50 Hz and 1% at +10 dBU primary level at 50 Hz.

The LL1538 is designed for PCB mounting with 5.08 mm pin spacing, 27.94 mm row spacing and a recommended PCB hole diameter of 1.5 mm. Its compact body measures 38 x 24 x 17 mm above the PCB and weighs 46 g. Isolation is rated at 4 kV between windings and 2 kV between windings and shield.