Lundahl LL1524 Audio transformer

LL1524 is an audio output transformer for balanced drive.  The LL1524 is a 5-section output transformer. This results in a very low leakage inductance and thus excellent HF characteristics. The LL1524 is  (like all C-core audio output transformers) ideally used with negative source impedance achieved using mixed feedback drive circuits. See separate paper for mixed feedback design principles.

Turns ratio: 1+1:1+1

Technical Details:

• Spacing between pins:                                                                                                     5.08 mm  (0.2")

• Spacing between rows of pins:                                                                                        35.56 mm  (1.4")

• Weight:                                                                                                                              125 g

• Core:                                                                                                                                   Audio C-core

• Housing:                                                                                                                             Mu-metal

• Rec. PCB hole diameter:                                                                                                   1.5 mm

• Static resistance of each primary:                                                                                    7.3 ?

• Static resistance of each secondary:                                                                                 7.5 ?

• Leakage inductance of secondaries (sec. in series):                                                        0.1 mH

• No-load impedance:                                                                                                           >1k? @ 50 Hz, +20 dBU

• Optimum source impedance:                                                                                            Minus 14 ?  (mixed feedback)

• Balance of output (according to IRT, source < 10 ? , Load 600 ?):                            > 45 dB

• Maximum output level before saturation (sec. in series, load 600 ?)                           +  24 dBU @ 30 Hz

• Distortion  (achieved with mixed feedback drive circuit, load 600 ?)                          < 0.04 % @ 20 dBU, 30Hz

• Frequency response (source 0 ?,  load 600 ?):                                                               5 Hz -- 100 kHz +/- 0.5 dB

• Loss across transformer (at midband with 600 ? load):                                                0.5 dB              

• Isolation between primary and secondary windings / between windings and core:    4 kV / 2 kV