Hammond 140MEX 100K to 1500 Ohm Shielded Microphone Transformer

The 140MEX is a studio grade impedance matching audio transformer with a 100K ohm primary and a 1500 ohm secondary. Its listed typical application is crystal or ceramic microphone to base, stepping a very high source impedance down to 1500 ohms, and the drawing also lists input/output isolation, line matching, driver and hybrid applications. It suits audio engineers, equipment restorers and OEM designers working at signal level.

The transformer uses an 80% nickel core for high permeability combined with low losses, and it operates across 20 Hz to 20 kHz (+/- 1 dB). It is designed for maximum bandwidth and lowest distortion at +10 dBm or less; output power is 10.0 dBm (marked 5 mW). The overall turns ratio is 8:1 (8.13:1 typical on the drawing).

Typical drawing values: primary DCR 5430 ohms, secondary DCR 159 ohms, primary inductance 2100 H and secondary inductance 34 H at 1 kHz, 1 V. Insertion loss is under 1.2 dB, return loss 30.0 dB, longitudinal balance -70 dB and dielectric strength 500 Vrms. Primary leads are RED - YEL (100,000 ohms) and secondary leads 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 140MEX is made in Canada and is RoHS and REACH compliant.