Lundahl LL7905 Audio transformer

The LL7905 is a large, high level, high performance audio transformer, made for extraordinary requirements. The transformer combines very high secondary level capability (+37 dBU [54.5V rms] @ 50 Hz ) with low copper resistance and is designed for the most demanding applications. The LL7905 consists of two coils, each with two primary and one secondary windings separated by electrostatic shields. The core is a high permeability mu metal lamination core.

Turns ratio: 1 + 1 + 1 + 1 : 5.6 + 5.6

Technical Details:

• Dims (Length x Width x Height above PCB (mm)): 66 x 32 x 21

• Spacing between pins: 5.08 mm (0.2")

• Spacing between rows of pins: 5.08 / 45.72 mm (0.2 / 1.8")

• Weight: 155 g

• Rec. PCB hole diameter: 1.5 mm

• Static resistance of each primary (average): 28 ohms?

• Static resistance of each secondary (average): 395 ohms????

• Distortion (primaries connected in series, source impedance 600 ohms ): + 10 dBU primary level, 50 Hz: 0.1 %

• Distortion (primaries connected in series, source impedance 600 ohms ): + 28 dBU primary level, 50 Hz: 1 %

• Self resonance point : 80 kHz

• Optimum termination for best square-wave response (Connections L4-R2 , source imp. 600 ohms ) : 30k ohms in series with 100pF

• Frequency response (source and load as above, connection L4-R2, secondary side balanced with or without grounded centertap. : 10 Hz - 55 kHz +/- 1 dB

• Frequency response (source and load as above, connection L4-R2, secondary side unbalanced with pin 23 grounded) 10 Hz - 30 kHz +/- 1 dB

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