Hammond 140QEX 600 Ohm CT Shielded Line Isolation Transformer

The 140QEX is a studio grade 1:1 audio transformer with a 600 ohm centre-tapped primary and a 600 ohm centre-tapped secondary. Its listed typical application is line to line isolation, and the drawing also names input/output isolation, line matching, driver and hybrid applications, so it fits studios, broadcast facilities and AV integrators needing to isolate balanced 600 ohm lines.

Both windings are centre tapped: the primary is RED - BRN - YEL and the secondary GRN - BLK - BLU, with 36.2 ohms DCR on each half (72.4 ohms per winding). Typical inductance at 1 kHz, 1 V is 10.62 H on each winding, with a measured impedance of 64.5 k on each side.

An 80% nickel core provides high permeability with low losses, and the drawing notes a mumetal can for shielding from a broad range of external sources. The 140QEX operates from 20 Hz to 20 kHz (1 dB) and is rated for 10.0 dBm output (marked 5 mW), designed for lowest distortion at +10 dBm or less. Insertion loss is under 1.1 dB, return loss 20 dB, longitudinal balance -65 dB and dielectric strength 500 Vrms.

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 drawing shows a 1.875 in mounting hole spacing. The part is made in Canada and RoHS and REACH compliant.