Sescom MI-11 Microphone Input transformer

These are Sescom input transformers that were manufactured in the early to mid 1970's.  The published technical specifications were not available, but we've provided the best information available based upon the specs of later versions (MI-12, MI-18, MI-19) along with designations in Sescom catalogs from the mid 1990s.  All of the Sescom transformers with the "MI" prefix were designed for Mic Input use.

The case uses 12 forked solder terminals in a circular pattern, the case is 1.75" tall x 1.2968" Square and has 8 tapped holes (4 top, 4 bottom) that accept 4-40 hardware.  The high 60KΩ secondary impedance makes these transformers a good choice for tube mic preamp circuits.  They can also be used for isolating High impedance IC or discrete inputs, or coupling low level balanced signals to an unbalanced input.

The specifications are as follows:

• PRIMARY: 150Ω/600Ω
• SECONDARY: 60KΩ
• Gain (estimated) 150Ω primary--17 db, 600Ω primary--23 db.
• Frequency Response: 20Hz--20KHz. +/- 1db
• Distortion <.2% @ 30Hz.
• Mu-Metal shielding
• Electrostatic shield

We were unable to locate any information regarding the maximum input level, but given that these are designed for mic level signals, it's likely to be in the -10 to 0 db range.