Lundahl LL1517, Audio Output Transformer

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