Lundahl LL1528 Microphone Input Transformer

Highlights of the Lundahl LL1528

• Microphone input transformer with 1 + 1 : 2.5 + 2.5 turns ratio
• Two-coil construction with primary and secondary sections separated by an electrostatic shield
• High-permeability mu-metal core housed in a mu-metal can
• Frequency response of 10 Hz to 40 kHz within ±0.3 dB under specified termination
• Isolation rated at 4 kV between windings and 2 kV between windings and shield

Product details Lundahl LL1528

Lundahl LL1528 Microphone Input Transformer

The Lundahl LL1528 is designed as a precision microphone input transformer for audio input circuitry. Its internal structure uses two coils, each with one primary and one secondary section, with an electrostatic shield between the sections to support clean signal transfer in sensitive low-level audio applications.

As a compact audio component, the LL1528 is built around a high-permeability mu-metal core and housed in a mu-metal can. The transformer measures 38 x 24 x 17 mm above the PCB and weighs 46 g, making it suitable for PCB-mounted microphone preamp and input-stage designs.

The LL1528 offers a 1 + 1 : 2.5 + 2.5 turns ratio, with connection alternatives for 1:2.5 and 1:5 use. With primaries connected in parallel and a 200 ohm source impedance, distortion is 0.2% at +0 dBU primary level at 50 Hz and 1% at +10 dBU primary level at 50 Hz.

Key electric measurements include 42 ohm static resistance per primary, 450 ohm static resistance per secondary and a self-resonance point above 80 kHz. For best square-wave response in 1:5 connection with a 200 ohm source impedance, the optimum termination is 9 kOhm in series with 3 nF.