Lundahl Line output transformer, LL1517

Audio Output Transformer LL1517

LL1517 is an audio output transformer for balanced or unbalanced drive. The transformer is built from two threesection coils, with primaries and secondaries separated by electrostatic shields, and a audio C-core of our own production. The transformer is housed in a mu-metal housing.

The LL1517 has sufficient low copper resistance to meet broadcast specifications in a conventional drive configuration, but is (as all output transformers) ideally used with mixed feedback drive circuits. (See separate paper for mixed feedback design principles).

Turns ratio: 1 + 1 : 1 + 1
Dims (Length x Width x Height above PCB (mm)): 47 x 34 x 18

Spacing between pins: 5.08 mm (0.2")
Spacing between rows of pins: 35.56 mm (1.4")
Weight: 105 g
Core: Audio C-core
Housing: Mu-metal
Rec. PCB hole diameter: 1.5 mm
Static resistance of each primary: 9.2 W
Static resistance of each secondary: 9.5 W
Leakage inductance of secondaries (sec. in series): 0.3 mH
No-load impedance: Typically > 600W @ 50 Hz, +20 dBU
Optimum source impedance: Minus 18 W (See above)
Balance of output (according to IRT, source < 10 W , Load 600 W): > 60 dB
Maximum output level before saturation (sec. in series, load 600 W) + 24 dBU @ 30 Hz
Distortion (achieved with mixed feedback drive circuit, load 600 W) < 0.03 % @ 20 dBU, 30Hz
Frequency response (source 10 W, load 600 W): 10 Hz -- 80 kHz +/- 0.3 dB
Loss across transformer (at midband with 600 W load): 0.3 dB
Isolation between primary and secondary windings / between windings and core: 4 kV / 2 kV