User Manual

Audio Output Transformer
LL1539
LL1539 is an audio output transformer for balanced drive.
In LL1539, the winding arrangement is such that (properly connected) the secondary windings are surrounded by cold
(neutral) parts of the primary windings. This reduces the effect of the capacitance between the primary and the
secondary windings. Thus, primaries should always be connected as in the application example below, with or without
current feedback drive (negative source impedance).
Turns ratio: 2 : 1 + 1
Dims (Length x Width x Height above PCB (mm)): 47 x 34 x 21
Pin layout (viewed from component
side) and winding schematics:
Spacing between pins: 5.08 mm (0.2")
Spacing between rows of pins: 35.56 mm (1.4")
Weight: 130 g
Rec. PCB hole diameter: 1.5 mm
Static resistance of each primary half (4 -- 1&6 or 3 -- 2&5 respectively): 20
Ω
Static resistance of each secondary: 20
Ω
Secondary leakage inductance (secondaries in series): 0.6 mH
No-load impedance: >2 k
Ω
@ 50 Hz, +20 dBU
Optimum source impedance: Minus 40
Ω
Balance of output (according to IRT, source < 10
Ω
, load 600
Ω):
> 65 dB
Maximum output level before saturation (load 600
Ω):
+ 24 dBU @20Hz
Frequency response (@ 10 dBU, source < 10
Ω
, load 600
Ω
): 20 Hz -- 60 kHz +/- 0.3 dB
Voltage loss across transformer (at midband with 600
Ω
load): 1 dB
Isolation between primary and secondary windings / between
windings and core: 4 kV / 2 kV
Application example: This schema shows the principles of mixed feedback circuitry for eliminating transformer-
induced distortion and for reducing output impedance. (NOTE! This application was covered by a now outdated
German patent DE 29 01 567 with application day 13.1.79)
Can + Core
10
3
2, 5
1, 6
4
7
8
12
11
+
_
Gain = 2 * Rf / Rin. Optimum R <= (Rin/Rf) * Rp / 2, where Rp is Cu resistance of prim.
Select R for good THD at LF and for good square wave response
6
5
4
3
2
12
11
10
8
1
7
_
+
+
_
Cin Rin
Rf
10k
R
10k
R010403
Simplified winding
schematic
Pin layout


Tibeliusgatan 7 International Domestic
S-761 50 NORRTÄLJE Phone +46 - 176 13930 0176-13930
SWEDEN Fax +46 - 176 13935 0176-13935
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2
3
4
5
7
8
10
11
6 12
LL1539
LL1539
(top view)