Hammond 1140-MN-A 150 to 15K Ohm 1:10 Microphone Step-Up Transformer

The 1140-MN-A is a 1:10 microphone step-up transformer from the 1140 Series of studio grade impedance matching transformers. It offers a high step-up ratio over the 20 Hz to 20 kHz range, and its typical application is the input stage of vacuum tube or FET style amplifiers, so it is aimed at microphone preamp designers and builders of tube and FET recording gear.

The impedance ratio is 150:15K with a 1:10 turns ratio. Rated performance is -2.5 dBu maximum input at 20 Hz, 0.02% THD at 20 Hz and a frequency response of -0.05 dB at 20 Hz and -0.06 dB at 20 kHz. The drawing lists maximum input level of -2.5 dBu at 20 Hz into RL = 15000 Ω, THD of 0.004% at 1 kHz and 0.005% at 20 Hz (-20 dBu), and common mode rejection of 90 dB at 60 Hz and 75 dB at 3 kHz.

The nickel core provides high permeability combined with low losses for a very wide bandwidth, and the mu metal can provides excellent shielding from a broad range of external sources. DCR is 24.0 Ω primary and 2400 Ω secondary at 20 °C, typical primary input impedance is 1.3KΩ at 1 kHz and -20 dBu, capacitance to shield and case is 350 pF primary and 375 pF secondary, and dielectric strength is 500 Vrms.

The 1140-MN-A is a shielded chassis mount part with colour-coded leads: orange/brown for the 150 Ω primary, green and green/yellow for the 15000 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).