Hammond 140NEX 50 to 1500 Ohm Shielded Dynamic Mic Transformer

The 140NEX is a studio grade impedance matching audio transformer that steps a 50 ohm primary up to a 1500 ohm secondary. Its listed typical application is dynamic microphone to base, and the drawing also names input/output isolation, line matching, driver and hybrid applications, making it relevant to studio technicians, restorers and designers of microphone preamp inputs.

An 80% nickel core provides high permeability with low losses, supporting a 20 Hz to 20 kHz operating range (1 dB). The series is designed for maximum bandwidth and lowest distortion at +10 dBm or less, and the 140NEX is rated for 10.0 dBm output (marked 5 mW). The table lists the overall turns ratio as 1:5:5; the drawing gives a typical 1:5.47.

Typical drawing values are 5.30 ohms primary DCR and 116.5 ohms secondary DCR, with 326 mH primary and 9.30 H secondary inductance at 1 kHz, 1 V. Insertion loss is under 0.9 dB, return loss 28.0 dB, longitudinal balance -70 dB, and dielectric strength 500 Vrms. The primary is on RED - YEL (50 ohms) and the secondary on GRN - BLU (1500 ohms).

It is a chassis mount, shielded transformer in a metal can with an adjustable height case bracket. The case is 1.00 in (25 mm) high and 1.25 in (32 mm) in diameter, mounting holes are listed at 1.88 in (48 mm), leads are 5.00 in (127 mm) long, and net weight is 3 oz (shipping weight 0.13 lbs / 0.06 kg). The 140NEX is made in Canada and RoHS and REACH compliant.