Microphone Input Transformers, Line-box Transformers
LL1576 and LL1577
The LL1576 and the LL1577 are high performance microphone input transformers/line-box transformers with high
permeability mu-metal cores and high bandwidth coils. The LL1576 and the LL1577 use the same pin-out as our well
known microphone transformer LL1538.
In both types, primary and secondary windings are separated by electrostatic shields. The very low leakage inductance
and thus excellent frequency response is achieved by a two-coil, three-section per coil winding structure.
The transformers are encapsulated in mu-metal cases for magnetic shielding.
Pin layout (component side view) and winding schematics:
Dimensions
Max. Length x Width x
Height above PCB (mm)
Spacing
between pins
Spacing between
rows of pins
Recommended PCB
hole diameter
Weight
38 x 24 x 17
5.08 mm (0.2")
27.94 mm (1.1")
1.5 mm
46 g
LL1576
LL1577
Turns ratio
1 + 1 : 7
1 + 1 : 14
Static resistance of each primary
50
Ω
12 Ω
Static resistance of secondary
1.5 k
Ω
1.5 k
Ω
Primary level at 0.2 % THD, 50 Hz signal
Primaries connected in parallel (fig b), source impedance 50
Ω
+2 dBU
(sec. level +19 dBU)
-4 dBU
(sec. level +19 dBU)
Primary level at 1 % THD, 50 Hz signal
Primaries connected in parallel (fig b), source impedance 50
Ω
+ 12 dBU
(sec. level +29 dBU
+6 dBU
(sec level +29 dBU)
Frequency response +/- 0.5 dB to balanced input
Signal level 0 dBU, source 200
Ω
, fig b, no termination
15Hz – 50kHz
30Hz – 12kHz
Frequency response +/- 0.5 dB to balanced input
Signal level -10 dBU, source 50
Ω
, fig b, load:
5Hz – 40kHz
30 k
Ω
+ 200pF
10Hz – 50kHz
80 k
Ω
+ 100pF
Isolation between windings / between windings and shield
4 kV / 2 kV
4 kV / 2 kV
2
3
4
5
6
1
8
R980402
Tibeliusgatan 7
International
Domestic
S-761 50 NORRTÄLJE
Phone
+46 - 176 13930
0176-13930
SWEDEN
Fax
+46 - 176 13935
0176-13935
8
2
1
3
4
5
6
LL1576
Fig. a. Primaries in series.
Turns ratio 1 : 3.5 with LL1576
Turns ratio 1 : 7 with LL1577
Connection alternatives
Component side
2
3
4
5
6
1
8
LL1576
2
3
4
5
6
1
8
LL1576
Fig. b. Primaries in parallel.
Turns ratio 1 : 7 with LL1576
Turns ratio 1 : 14 with LL1577
The transformers are often used reversed (7:1 or 14:1) for example in line boxes.
