Audio Transformer
LL1550
LL1550 is an audio transformer with rather high turns ratio and with a variety of connection alternatives. The
transformer is built up from two coils, each with a secondary winding surrounded by shields and two primary
windings. This structure results in an excellent frequency response. All winding ends are available on the pins.
The transformer is ideally used in applications where the high turns ratio is utilized, e.g. in a D.I. box.
The LL1550 is made with amorphous core material. As this type of core does not store energy (unlike
conventional mu-metal cores) the low frequency resonance with external capacitors is practically eliminated.
Refer to the backside of this sheet for termination alternatives.
Turns ratio:
1 + 1 + 1 + 1 : 4 + 4
Dims: (Length x Width x Height above PCB (mm))
30 x 22.5 x 14.5
Pin Layout (viewed from pins side) and Windings Schematics:
Spacing between pins:
2.54 mm (0.1")
Spacing between rows of pins:
22.86 mm (0.9")
Weight:
30 g
Rec. PCB hole diameter:
1.5 mm
Static resistance of each primary (average):
33
Ω
Static resistance of each secondary (average):
265
Ω
Self-resonance point:
> 280 kHz
Recommended load for best square-wave response
(Termination alternative A below):
6.7 k
Ω + 470
pF
Frequency response
(source 150
Ω
, load (6.7 k
Ω + 470
pF) in parallel with 56 k
Ω
):
10 Hz - 70 kHz +/- 0.5 dB @ 0 dBU
Loss across transformer (at midband with termination as above):
0.3 dB
Core:
Amorphous Strip
Isolation between windings / between windings and shields:
3 kV / 1.5 kV
Data at different termination alternatives, showed on the back side of this sheet:
Termination
Alternative
Turns
ratio
Copper Resistance
prim/sec
Idle impedance
@40 Hz, 0dBU
Suggested Use
THD < 0.5%@40 Hz
primary level /
real source impedance
A
1:2
130
Ω
/ 530
Ω
40k
Ω
/ 160k
Ω
600
Ω
/ 10 k
Ω
12 dBU / 150
Ω
B
1:2
33
Ω
/ 133
Ω
10k
Ω
/ 40k
Ω
200
Ω
/ 10 k
Ω
6 dBU / 40
Ω
C
1:4
33
Ω
/ 530
Ω
10k
Ω
/ 1600k
Ω
200
Ω
/ 5k
Ω
6 dbU / 40
Ω
D
1:4
8
Ω
/ 133
Ω
2.5k
Ω
/ 40k
Ω
200
Ω
/ 1k
Ω
-1 dBU / 10
Ω
E
1:8
8
Ω
/ 530
Ω
2.5k
Ω
/ 160k
Ω
200
Ω
/ 10k
Ω
-1 dBU / 10
Ω
F (Split) 4:1+1 530
Ω
/ 66
Ω + 66Ω
G (Split) 1:2+2 33
Ω
/ 265
Ω + 265Ω
Left side can also be connected as B
CenterTap
(1:1+1) or D (1:2+2)
.
R940912
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Tibeliusgatan 7
International
Domestic
S-761 50 NORRTÄLJE
Phone
+46 - 176 13930
0176-13930
SWEDEN
Fax
+46 - 176 13935
0176-13935
