Line input audio transformers

Line input transformers are used to protect audio line inputs in studio
and live equipment from picking up external noise, caused by,
for instance, ground loops or cable noise pickup.

Line input transformers should have a high signal level capability, high no-load impedance and high Common Mode Rejection Ratio, CMRR.

Even short cables connecting two audio devices may sometimes pick up noise such as radio signals from cellphones or other transmitters around the setup. Such signals are however of common mode character, and are efficiently blocked by the Faraday shields in the input transformer.
The degree of the capability of the transformer to block such
signals is expressed as the transformer’s CMRR.

Ground loop noise can be induced when there is a direct (galvanic) connection between the signal source and receiver, and there is a ground level potential between them. This can occur, for example, when devices are connected to different wall outlets. It can also occur when lighting dimmers are connected to the same power distribution system as audio equipment, as dimmers have a tendency to make the electrical ground reference very noisy. But as the primary and secondary windings in an input transformer are galvanically isolated,
line input transformers eliminate ground loops.

A line input transformer will also take care of any balance-unbalance or unbalanced-balanced conversion needed if both balanced
and unbalanced equipment are used.

Line input

PhotoTypeTurns RadioSize LxWxHMax PrimlevelApplications / Comments
LL15311+1:2 28x17x15+20 dBU Small size
LL15401+1 :1+1 38x24x17+30 dBU High level input
LL1544A1+1+1+1 : 2+2 30x22.5x14.5+20 dBU Amorphous strip core. General purpose with many connection alternatives.
LL1545A1+1+1+1 : 2+2 38x24x17+22 dBU General purpose with many connection alternatives.
LL1545E1+1 : 1+1 38x24x17+22 dBU Line input transformer based on LL1545A, but with less pins and with all windings internally split between coils for symmetry.
LL15921+1 : 1+1 47x28x20+31 dBU High level line input transformer for extra demanding applications
LL19221+1 : 4+4 47x28x24+26 dBU High level stepup line input. Similar to the UTC LS-10.
38x24x17+9 dBU
+22 dBU
Dual input for consumer AND pro audio equipment
LL79011+1+1+1 : 1+1+1+166x32x21+34 dBU Very high level, high impedance input.
LL79021+1+1+1 : 1+1+1+1 66x32x21+28 dBU General purpose. Very high quality line input for 1:1, step-down or step-up.

Line input for ZF input circuits

PhotoTypeTurns RatioSize LxWxH Max Primlevel Applications / Comments
LL64041 : 115.5x11x10N/AFor Zero Field input circuitry (see datasheet)
LL71011+1 : 1.4 28x18x10N/A (Very high!) For Zero Field input circuitry (see datasheet)

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