EE08 universal Board for Lundahl Transformers LL1527, LL1527A, LL1528, LL1530, LL1538, LL1540, LL1545E, LL1570, LL1571, LL1578, LL1579, LL1581, LL1670, LL1935, LL1951, LL1952, LL4611.

Universal board EE08

Update: (First published: 05/23/2019 11:17)

LL1527, LL1527A, LL1528, LL1530, LL1538, LL1540, LL1545E, LL1570, LL1571, LL1578, LL1579, LL1581, LL1670, LL1935, LL1951, LL1952, LL4611.

Are these transformers difficult to use?

Of course not!

About half of the users of these small transformers are OEM, which have their own PCBs.

The other half is companies and DIY, which need only one pair. Some know exactly what they want and how to achieve this.

Testing and experimenting: Some others need to try out a few things first, by soldering loose wires on the pins. This becomes difficult, when result is not as expected. At a problem, you have not received a transformer with open or shorted windings, but you have made a mistake with the wiring, or with the schematic. Do not test the transformer with a multi meter as this will magnetize the core permanently, and that is hard to solve.

A challenge with fault finding is, any error occurs always at all windings at the same time. That is because all windings are transformer coupled. The Design Notes cover some of this, but using the EE08 board, means prevent such mistakes right from the beginning.

Moreover the transformer pins are not made for repeated soldering. All of this is solved by the EE08 board.

The EE08 board can do two things:

Use it as a complete board, with the Lundahl data sheet applications, and some more applications. We have added all of these in the configuration examples in the table below. This is in how such a transformer could be used. This uses the small matrix field at the PCB bottom to make the windings connections. More about complete board application.
Use it as a break out board. This is when you want to hard wire the transformer externally. Mostly for experiments with lots of cables attached. When it works, you can either leave it as is. Or, remove everything, and rewire it as complete board, which results then in shorter and cleaner wiring. More about the Break Out board application.

Features of EE08 PCB

Length x Width: 70mm x 46mm
Mounting Hole distance: 62.2 x 38.1mm (hole center)
Mounting Hole diameter: 3.5mm
Gold plated with ground plane at each side. The ground plane is not directly visible, because the black solder mask is over it, but it is gold plated as well.
The ground plane also closes the opening the transformer has, at the bottom.
Much better behavior compared too loose wires. A 150kHz sine wave is passed without any loss, and also a 1kHz Square wave without any overshoot at all, with LL1570 (See below).
Core + Can are connected, if such a connection exists on the transformer itself.
Transformer's static shield is connected, if such a connection exists on the transformer itself.

1. Use EE08 as Input/Output Board

This PCB can replicate the many data sheet applications of Lundahl. See below table for connections. Or, implement your own application, by making the connections on the wiring field.
All grounding schemes are possible, with Solder Bridges: EP, 8, A, B or C.
There is room for termination components C1, C2, R1, R2. Initially it works also without.
Effectively, EVERYTHING as in all data sheets can be realized with this PCB.

For testing, do not use an Ohms meter. This will magnetize the core. For measurements, do so with AC signal only. Also read under "Notes".

Mounting the transformer. Some transformers will fit in the board only in one position. For transformers, which also can be mounted rotated, these must be inserted with it's text oriented the same way as on the PCB.

Double check this: At the board, Pin1 is marked with a square. Double check in the data sheet, where is Pin1.

Primary Load: If the application requires it, a resistive load it can be added across the primary, use the lower row for this, and solder the resistor on the corresponding Pins. Example: When a load of 1k is required from Pin1 to Pin3, insert the resistor in the holes 1 and 3. Each of the three horizontal rows is identical. It is that easy.

Secondary Load: For higher impedance transformers, it is often useful to add a small RC networks across the secondary. Such transformers will work such a network as well, so add the network in the end, of you find the board works good for the rest of it. If there is no RC network in the data sheet, it is not needed. Example: If by the data sheet, an RC network is needed between Pin7 and Pin8, connect the Resistor with one end to 7 and the other end to R1. Connect the Capacitor with one end to 8, and the other end to C1. In the case of two RC networks, like with a splitter, the second pair is connected to R2 and C2. It is that easy! Example is here.

Ground. WIth some special transformers, Pin8 must be grounded. You will see this in the data sheet of the transformer itself. If so, close Solder Bridge 8.

In the Lundahl data sheets, you will see a primary ground EP with some transformers. Sometimes it is needed to connect this externally to circuit ground. Om that case, use the solder island EP for this. In some other cases, only EP must only be grounded. In that case insert Solder Bridge EP. All grounding schemes are already in the data sheets. Just do it as it writes there. Some transformers have internal shields, called EP, E, E1 and E2. Unfortunately, Lundahl did not use uniform numbering for the secondary shields, but a short look at each of the data sheets, will show you the right lettering. To have it not confused from our side, we called the secondary shields. A, B, C, and we do not use the letters E, E1, E2 on the PCB.

Function of solder bridges:

Apply a solder drop, and these pins are grounded;

EP: Primary shield.(if the transformer has such a shield).
A: Static shield of winding, belonging to Pins 7-8.(if the transformer has such a shield).
C: Static shield of winding, belonging to Pins 6-8.(if the transformer has such a shield).
B: Static shield of winding, belonging to Pins 5-6.(if the transformer has such a shield).
8: Grounds Pin8.

For this, just check the Lundahl data sheet, of the transformer of your choice. In case there is an internal shield, you will quickly understand the logic. Then, you can connect E1, E2, or E, to the chassis ground, by closing Solder Bridges A, B, or C. Read also the notes, under "Grounding"

Asymmetric Output (One signal wire only, which signal is vs. ground)

Though this is not specifically mentioned in most data sheets, it is a possible application for all transformers. For this, (only) Pin 8 can be grounded. It this case, it becomes a none data sheet application, but such can be many. Begin with grounding Pin8, by adding a solder drop on bridge J8. Then, from there decide if the secondaries are in parallel or series, and connect this accordingly, with wire pieces on 5,6,7,8. This may have reversed the secondary polarity, because Pin8 is 'plus'. So to correct for this, In+ becomes In- and In- becomes In+. Like this the polarity is restored again. The Output signal is now one wire only, against PCB ground. So the PCB MUST be grounded now, with a wire at the Ground Symbol connection, and in addition via the mounting screws is always a good thing to do.

2. Use EE08 as Break Out Board.

The bottom part is unused, and the side connections of the PCB, correspond with the data sheet pin numbers. Just connect it to your own circuit, without wire mess.
No risk to damage the transformer pins by soldering.
At a later moment you can still see how how it is connected.
The lower section, where is says in the picture "This section is not used" is convenient still to test electrical signals, since numbering is the same as transformer pins.

Connection examples

Function of Solder Bridges

These will ground specific pins of the transformer.

In the examples below here, this is already marked. The information in this text box here, is only needed when you make your own configuration.

Bridge EP: Grounds the Primary shield.
Bridge A: Grounds shield belonging to windings of Pins 7-8.
Bridge B: Grounds shield belonging to windings of Pins 5-6.
Bridge C: Grounds shield belonging to windings of Pins 6-8.
Bridge 8: Grounds Pin8.

Jump in the table to:

LL1527 - LL1527A - LL1528 - LL1530 - LL1540 - LL1545E - LL1570 - LL1571 - LL1578 - LL1579 - LL1591 - LL1670 - LL1935 - LL1951 - LL1952 - LL4611

Line#

Connect

In / Out

Termination

1

LL1527

Serial-Serial 1:1

High impedance input

Standard configuration

At Connection Field,
wire from:

1 to 3.
6 to 8.

Insert Solder Bridge C

Pin4= In+
Pin2= In-

Pin5= Out+
Pin7= Out-

Connect Chassis to Ground Symbol

At Connection Field, 3k9 from 5 to 7

2

LL1527

Parallel-Parallel 1:1

Medium impedance input

Sometimes reduces noise of pre-amp.

At Connection Field,
wire from:

1 to 4.
2 to 3.
6 to 7
5 to 8.

Insert Solder Bridge C

Pin4= In+
Pin2= In-

Pin5= Out+
Pin7= Out-

Connect Chassis to Ground Symbol

At Connection Field, 3k9 from 5 to 7.

3

LL1527

Parallel to serial 1:2

Low impedance input

Gives Signal gain, but also increases noise of pre-amp.

At Connection Field,
wire from:

1 to 4.
2 to 3.
5 to 7.

Insert Solder Bridge C

Pin4= In+
Pin2= In-

Pin8= Out+
Pin6= Out-

Connect Chassis to Ground Symbol

At Connection Field, 3k9 from 6 to 8.

4

LL1527

Serial to Parallel 2:1

New configuration

High impedance input

Reduces noise of pre amp.

At Connection Field,
wire from:

1 to 3.
6 to 7.
5 to 8.

Insert Solder Bridge C, this grounds PIn-E of the transformer.

Pin4= In+
Pin2= In-

Pin7= Out-
Pin5= Out+

Connect Chassis to Ground Symbol

At Connection Field, 1k5 from 5 to 7.

Tested: 10...150kHz @0.2dB

150kHz Sine

1kHz Square

5

Some Applications for LL1527

XLR Input. XLR1 to Ground Symbol. XLR2 to In+, XLR3 to In-
Floating RCA Input (Balanced). This needs an "isolated ground" RCA connector. Cable shield to In-, RCA Center Pin to In+.
Floating RCA + XLR. Attach simultaneously both connectors is also possible.
Grounded RCA Input: RCA Center pin to In+. In- to Ground Symbol. (Floating RCA recommended)
Noise-reduction

6

About the EXAMPLES here. It applies not only to LL1527.

we can not make examples for every possibility. But this is not needed. Just check in the given examples of LL1527, how the wiring corresponds with the text instructions, and you will see this is done completely logical. Also when it works, it is often very easy to change to another amplification or attenuation ratio. If this is so, you are encouraged to try this out. In many cases, users have too much gain in the chain, and in such a case, reducing the gain will also reduce noise with the reduction factor. Like here above with LL1572 change "serial-serial 1:1" to "serial-parallel 2:1", means only change to small wire links. (remove 6-8, and add 6-7 and 5-8). If you already know, you may want to change the gain often, using the board EE21 may be a good idea as well, because it can produce factors from 0.5 to 4x gain, with the same transformer, a piano switch on the board.

7

LL1527

Splitter. 1: 1+1

Medium impedance input

At Connection Field,
wire from:

1 to 4.
2 to 3.

Insert Solder Bridge C

Pin4= In+
Pin2= In-

Pin8= Out+(1)
Pin7= Out(1)
Pin5= Out+(2)
Pin6= Out(2)

Connect Chassis to Ground Symbol

2x 6k8
connect at array from 7-8 and from 5-6

8

LL1527A