Hammond 1140-MN-B 150 to 3.8K Ohm 1:5 Microphone Step-Up Transformer

The 1140-MN-B is a 1:5 microphone step-up transformer in the 1140 Series of studio grade impedance matching transformers. It operates in the 20 Hz to 20 kHz range, and its typical application is the input stage of vacuum tube or FET style amplifiers. With a lower step-up ratio than the 1140-MN-A, it accepts higher microphone levels, which suits preamp designers working with louder sources.

The impedance ratio is 150:3.8K with a 1:5 turns ratio. Rated performance is +7.0 dBu maximum input at 20 Hz (RL = 600 Ω on the drawing), THD of 0.015% at 20 Hz per the series table, and a frequency response of -0.04 dB at 20 Hz and +0.00 dB at 20 kHz. The drawing gives typical THD of 0.015% at 1 kHz and 0.001% at 20 Hz (-20 dBu) and common mode rejection of 90 dB at 60 Hz and 75 dB at 3 kHz.

Its nickel core provides high permeability combined with low losses for a very wide bandwidth, and the mu metal can shields it from a broad range of external sources. DCR is 17.25 Ω primary and 450 Ω secondary at 20 °C; typical primary input impedance is 1.7KΩ and secondary output impedance 4.6KΩ at 1 kHz and -20 dBu; capacitance to shield and case is 780 pF primary and 450 pF secondary; dielectric strength is 500 Vrms.

The 1140-MN-B is a shielded chassis mount part with colour-coded leads: orange/brown for the 150 Ω primary, green and green/yellow for the 3800 Ω secondary, grey shield and violet can. It is RoHS and REACH compliant, made in Canada, and ships at 0.2 lbs (0.09 kg).