Line in and output audio Transformers
Line input audio transformers are used to protect audio line inputs in studio
and live equipment from picking up external noise, caused by,
for instance, ground loops or cable noise pickup.

Line input transformers should have a high signal level capability, high no-load impedance and high Common Mode Rejection Ratio, CMRR.

Even short cables connecting two audio devices may sometimes pick up noise such as radio signals from cellphones or other transmitters around the setup. Such signals are however of common mode character, and are efficiently blocked by the Faraday shields in the input transformer.
The degree of the capability of the transformer to block such
signals is expressed as the transformer’s CMRR.

Ground loop noise can be induced when there is a direct (galvanic) connection between the signal source and receiver, and there is a ground level potential between them. This can occur, for example, when devices are connected to different wall outlets. It can also occur when lighting dimmers are connected to the same power distribution system as audio equipment, as dimmers have a tendency to make the electrical ground reference very noisy. But as the primary and secondary windings in an input transformer are galvanically isolated,
line input transformers eliminate ground loops.

A line input transformer will also take care of any balance-unbalance or unbalanced-balanced conversion needed if both balanced
and unbalanced equipment are used.

For Breakout PCB's, check here



Model
Turns
Ratio
Size
LxWxHmm
MAX
Prim Level
Comments
Price
USD
1+1:2
28x17x15
+20dBU
small size
63.00
1+1:1+1
38x24x17
+30dBU
High level input
71.00
1+1+1+1:2+2
30x22.5x14.5
+20dBU
Amorphous strip core. General purpose with many connection alternatives
87.00
1+1+1+1:2+2
38x24x17
+22dBU
General purpose with many connection alternatives
77.00
1+1:1+1
38x24x17
+22dBU
Line input transformer based on LL1545A, but with less pins and with all windings internally split between coils for symmetry.
84.00
1+1:1+1
47x28c20
+31dBU
High level line input transformer for extra demanding applications
98.00
1+1:4+4
47x28x24
+26dBU
High level stepup line input. Similar to the UTC LS-10
104.00
1:4
1:1
38x24x17
+9dBU
+22dBU
Dual input for consumer and pro equipment
77.00
1+1+1+1
:1+1+1+1
66x32x21
+34dBU
Very high level and high impedance input
143.00
1+1:1+1
66x32x21

+28dBU
General purpose. Very high quality line input for 1:1, step down or step up
141.00
Line Input audio Transformers
Model
Turns
Ratio
Size
LxWxHmm
MAX
Prim Level
Comments
Price
USD
1:1
15.5x11x10
N/A
For Zero Field input circuitry (see datasheet)
61.00
1+1:1.4
28x18x10
N/A (Very High)
For Zero Field input circuitry (see datasheet)
59.00
Line Input for ZF input circuits
Line output transformers with silicon iron C cores.

General properties
Compact
Low copper resistance
High level capability
For balance or unbalance drive
Lundahl silicon iron C cores

Driving circuitry for line output transformers should have low output impedance. In order to reach the very best performance in terms of low distortion and low line output impedance, we recommend that our output transformers are used with mixed feedback drive circuitry for negative output impedance and best THD performance.

In the book “OP AMP APPLICATIONS” (Analog Devices, edited by Walt Jung) the use of (op amps and) audio transformers in line input and output applications are discussed in depth. In particular the mixed feedback drive circuits for line output transformers are analyzed in great detail. We strongly recommend the book for anyone who is designing with op amps in general, and in particular if you are designing circuits for transformer line output applications.

The book is available on-line at https://www.analog.com/en/education/education-library/op-amp-applications-handbook.html. The mixed feedback circuitry is discussed in Section 6 (3.2Mb), page 6.71 and forward.

Sectioning of transformers are discussed in a separate paper.


Line output transformers

Model
Turns
Ratio
Size
LxWxHmm
MAX
Prim Level
Comments
Price
USD
1+1:1+1
47x34x19
+24dBU
Universal ouput
70.00
2:1+1
47x34x21
+27dBU
For balanced drive
63.00
1+1+1+1:1+1
33x26x20
+27dBU
For balanced drive. Small size
58.00
1+1:1+1
48x34x22
+24dBU
For balanced drive
63.00
1+1:1+1
31x26x23
+24dBU
For balanced or unbalanced drive. Pin compatible with the LL2811, but with internal electrostatic shields.
74.00
1+1:1+1
47x34x21
+30dBU
High level universal output transformer
76.00
1+1:1.4+1.4+ 0.3+0.3
66x39x53
+25dBU
Single End class A, 100mADC. For solid state SE output circuits, based on the LO1166A
104.00
1+1:1:1
31x26x23
+24dBU
For balanced drive. Four section windings. Small footprint. Fits three in a row across Euroboard
62.00
2:1+1
43x28x21
+18dBU
For unbalanced drive.
61.00
1+1:1+1
47x34x17
+20dBU
For balanced drive.
59.00
Line output transformers
Model
Turns
Ratio
Size
LxWxHmm
MAX
Prim Level
Comments
Price
USD
2+2:1+1+1+1
47x34x23
+20dBu
For balanced drive. Four independent outputs active split.
81.00
1+1:1+1+1+1
47x34x23
+23dBU
For balanced drive. Four independent outputs active split.
81.00
Active output splitting transformers (for active press boxes)
To place an order, please click here
To place an order, please click here
Breakout pcb's for Lundahl audio transformers