Lundahl Line output transformer, LL7401

Audio Output Transformer LL7401

LL7401 is an audio output transformer for balanced drive. In LL7401 a five section winding structure is used. This results in a very low leakage inductance without high capacitive coupling and low isolation voltage, which are drawbacks of the bifilar winding technique.

Turns ratio: 1 + 1: 1 + 1
Dims (Length x Width x Height above PCB (mm)): 47 x 34 x 17

Spacing between pins: 5.08 mm (0.2")
Spacing between rows of pins: 35.56 mm (1.4")
Weight: 92 g
Rec. PCB hole diameter: 1.5 mm
Static resistance of each primary: 9 W
Static resistance of each secondary: 9 W
Leakage inductance of secondaries (sec. in series): 50 H
No-load impedance: >700 W @ 50 Hz, +20 dBU
Optimum source impedance: Minus 9 W (See application below)
Balance of output (according to IRT, source < 10 W, Load 600 W): > 60 dB

Note! Performance figures below are obtained using mixed feedback drive circuits. (See application example).Otherwise use lowest possible source impedance

Distortion (connection as application example below, load 600 W) 0.05 % @ +22 dBU, 50 Hz
Frequency response (@ 10 dBU, connections as below, load 600 W): 20 Hz -- 80 kHz +/- 0.3 dB
Voltage loss across transformer (at midband with 600 W load): 0 dB
Isolation between primary and secondary windings / between windings and core: 4 kV / 2 kV

Application example with mixed feedback: (NOTE! This application is covered by a German patent DE 29 01 567 with application day 13.1.79, valid as far as we know in Germany only).