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Reslo LTU1 line matching unit manual

When home recording with  reel-to-reel tape machines was a popular hobby, back in the 1960s and 70s, many recorders had only high impedance inputs. However, the low impedance microphones of the time could be used with a longer cable without signal degradation, and so most manufacturers offered matching transformers to plug that gap.

Other transformers were also available to match medium and high impedance microphones to low impedance inputs, and so on. But the Low-to-High is by far the most common.

Here is a scanned manual for the Reslosound LTU1 line matching unit, which was used to connect 15Ω to 50Ω ribbon microphones to a high impedance tape deck. This was superseded by the LMT, which is essentially the same thing in a smarter metal can.

Reslo impedance matching transformer.