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!

Some need to try out a few things first, by soldering loose wires on the pins. This has some risk. When the wire is too thick, you would rotate the pin, when bending the wire. This will break off the internal wire, and the transformer is damaged.

If a set up doesn't work, many seem to suspect, a defective transformer was supplied, and people test the windings with a multi meter. However the multi meter injects 1mA into the winding, and the core becomes permanently magnetized. Better trust, the transformers are already tested by Lundahl, and rather a non working circuit means a wring error was made.

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, prevents wiring mistakes from the beginning.

Moreover the transformer pins are not intended for repeated soldering. This will loosen the pins, and the internal wiring can break off. All of this is solved by the EE08 board.

Click here for full size schematic

The EE08 board can do two things:

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.
Use it as a complete board, with the Lundahl data sheet applications. We have added all of these (and a few more) 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.

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 Break Out Board.

The matrix section is not used, and the side connections of the PCB, correspond with the data sheet pin numbers. Just connect this to your own circuit, the way you want it.

2. Use EE08 as Input/Output Board

This PCB replicates 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, they way you want it yourself. (Circuit Diagram is here)
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, Terminal1 is marked with a square. Double check in the data sheet, where is Terminal1.

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 Terminal1 to Terminal3, insert the resistor in the holes 1 and 3. Each of the vertical rows are connected to each other. So it doesn't matter which "1" or "3" you take.

Secondary Load: For higher impedance transformers, it is often useful to add a small RC networks across the secondary. These transformers work without such a network as well, so don't bother about this from the beginning. Add the network as final touch.

Example: If by the data sheet, an RC network is needed between Terminal7 and Terminal8, 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, add a solder drop on 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. In that case, use the solder bridge EP for this. 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.

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 Terminal8, 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 Terminal8 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.

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 Terminal8

Do you have Star Ground, or Chassis Ground?

Good grounding is the key to a hum free result, but I guess you already knew this :) The PCB ground plane by itself is not connected to anything. In the standard use situation, the ground plane becomes connected to the chassis via the four mounting screws. From here, you can decide which of the transformer pins you would like to connect to the chassis, by placing a solder drop on the ground bridges. (See overview above here). This solder drop can easily by removed again. The common use is, when the PCB ground plane is also signal mass. This will be the case when you have no star ground system, or no ground wire bar. In this situation, chassis mass and signal mass become the same. We supply the EE08 PCB with metal space holders, for this use.

In case of star grounding (or a thick wire ground bar, which has the same effect), the chassis is not used for electrical signal, and serves instead as a shield. This shield is connected to the signal mass, at the lowest signal point, which is normally the amplifier input. Yet, also this connection carries no signal current, because nothing is connected to it. In this case, the PCB should be mounted with plastic space holders, and plastic screws, and the ground symbol of the PCB will be connected to the star ground.

Jump in the table to:

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

Click here for full size schematic

Line

Connections

1

LL1527 (XL)

Serial-Serial 1:1

High impedance.

Standard configuration

INPUT

At Connection Field,
wire from:

1 to 3
6 to 8.

Insert Solder Bridges:

C only.

Terminal4= In+
Terminal2= In-

Terminal5= Out+
Terminal7= Out-

Connect Chassis to Ground Symbol.

TERMINATION

At Connection Field, 3k9 from 5 to 7

2

LL1527 (XL)

Parallel-Parallel 1:1

Medium impedance input

Sometimes reduces noise of pre-amp.

INPUT

At Connection Field,
wire from:

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

Insert Solder Bridges:

C only.

Terminal4= In+
Terminal2= In-

Terminal5= Out+
Terminal7= Out-

Connect Chassis to Ground Symbol.

TERMINATION

At Connection Field, 3k9 from 5 to 7

3

LL1527 (XL)

Parallel to serial 1:2

Low impedance input

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

INPUT

At Connection Field,
wire from:

1 to 4
2 to 3
5 to 7

Insert Solder Bridges:

C only.

Terminal4= In+
Terminal2= In-

Terminal8= Out+
Terminal6= Out-

Connect Chassis to Ground Symbol.

TERMINATION

At Connection Field, 3k9 from 6 to 8.

4

LL1527 (XL)

Serial to Parallel 2:1

New configuration

High impedance input

Reduces noise of pre amp.

INPUT

At Connection Field,
wire from:

1 to 3
6 to 7.
5 to 8

Insert Solder Bridges:

C only.

Terminal4= In+
Terminal2= In-

Terminal7= Out-
Terminal5= Out+

Connect Chassis to Ground Symbol.

TERMINATION

At Connection Field, 1k5 from 5 to 7

Tested: 10...150kHz @0.2dB

150kHz Sine

1kHz Square

5

Some Applications for LL1527 (XL)

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

Splitter
1 : 1+1

LL1527 (XL)

Medium impedance input

Separated Outputs.

INPUT

Terminal4= In+
Terminal2= In-

At Connection Field,
wire from:

1 to 4
2 to 3

Insert Solder Bridges:

C only.

OUTPUT

At Connection Field,
wire from:

Terminal8= Out+(1)
Terminal7= Out(1)

Terminal5= Out+(2)
Terminal6= Out(2)

Connect Chassis to Ground Symbol.

TERMINATION

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

Both outputs have the same phase

8

PP driver
1 : 1+1

LL1527 (XL)

Medium impedance input

INPUT

Terminal4= In+
Ground = In-

At Connection Field,
wire from:

1 to 4
2 to 3
5 to 7

Connect Terminal2 to Ground Symbol

OUTPUT

Terminal8= Out+
Terminal6= Out-

Insert Solder Bridges: :
A and C

Connect Chassis to Ground Symbol.

TERMINATION

2x 2k7. Connect at array from 7-8 and from 5-6.

Termination gives best square wave response.

Both outputs have opposite phase

9