OPERATING INSTRUCTIONS

LEHLE P-ISO

LEHLE P-ISO#

Dear Musician!

Thank you for purchasing your LEHLE P-ISO!

I have been building units that switch, split and route signals with no technical compromises and with maximum musical fidelity since 1999. With the LEHLE P-ISO, you have purchased a product in which only the best components are used. Every assembly of your LEHLE P-ISO has been made and tested in Germany.

Your LEHLE P-ISO is of extremely robust design and construction, to make sure that you get absolutely years and years of enjoyment from it. If you should nonetheless have a problem, or simply a question, just mail me or a member of the Lehle team at: support@lehle.com

I wish you the very greatest pleasure and success using your LEHLE P-ISO!

Introduction#

The LEHLE P-ISO combines passive isolation with the highest possible signal fidelity.

Its applications range from isolation and eliminating hum, to balancing and reamplification along with any signal routing that requires a clean signal free from noise.

At its core is the high-end LEHLE TRANSFORMER HZ, which galvanically isolates the signal, eliminating any possibility of ground loops.

The LEHLE TRANSFORMER HZ was specially designed for use with high-impedance signals but also processes lowimpedance signals with uncompromising sound quality.

The classic application for the LEHLE P-ISO is as a hum suppressor. Frequently background noise caused by ground loops occurs when two electronic devices are connected to each other.

The LEHLE P-ISO provides a simple, but extremely effective remedy when installed between the two units. Using the ISO output, the devices are galvanically isolated and background noise becomes a thing of the past.

By using two amplifiers, driven by one stereo effects device, the LEHLE P-ISO can successfully isolate one amplifier from the other.

Thanks to its ability to pick off an unbalanced or balanced signal on the ISO output, the LEHLE P-ISO is also eminently suitable as a reamplification device or as a high-quality compact DI box for all signal types.

And just in case you are looking for a power connection:

the LEHLE P-ISO performs all its functions without any need for a power supply.

And due to its optimised size and low weight, it fits easily below your pedalboard or in any pocket.

Technical Data#

Weight206 g
Length71,5 mm
Width41 mm
Overall height31 mm
Max. Level+20 dBu (THD < 1%, 50 Hz – 20 kHz)
Total harmonic distortion0,003 % (0 dBu, 1 kHz)
Frequency range
20 Hz – 100 kHz -0,1/ +0,4 dB
(source 600 Ω, load 1 MΩ)
Input impedance
(transformer load impedance)		min. 2 MΩ bei 2 kHz

Signal Line Types#

UNBALANCED SIGNAL ROUTING#

Unbalanced signal lines predominate when instruments such as guitars, basses and keyboards are used.

These signal lines have two conducting cores.

The signal itself is present on the signal conductor and is connected to the tip of the jack plug.

The second core, which is connected to the sleeve of the jack plug, screens the signal conductor and constitutes the signal ground.

UNBALANCED SIGNAL ROUTING

JACKCABLEJACK
SleeveGroundSleeve
TipSignal in phaseTip

BALANCED SIGNAL ROUTING#

Balanced signal lines are used to cross larger distances without interference.

They are generally fitted with XLR connectors or TRS (Tip Ring Sleeve) jack plugs.

Here, three cores are required:
there are two signal conductors.

In a balanced signal line, the signal is present in phase at the tip, as in the case of an unbalanced signal line (XLR Pin 2). The second signal conductor carries the same signal, but with the opposite polarity or mirror-image phase (Ring, XLR Pin 3). The third conductor is the screening, and again constitutes the signal ground (Sleeve, XLR Pin 1).

BALANCED SIGNAL ROUTING

JACKCABLEXLR
SleeveGroundPin 1
RingSignal in mirrored phasePin 3
TipSignal in phasePin 2

General Description#

1. Input Socket
2. ISO Output

1. INPUT SOCKET 

Connect the output from an effects unit, keyboard or DAW here. 

The input signal is fed into this socket. The LEHLE P-ISO operates entirely passively. The input signal remains connected to the ISO output at all times, with no semiconductors or any other active components in the signal path. 

The signal can be either balanced or unbalanced, since the LEHLE TRANSFORMER HZ is capable of handling both types. 

2. ISO OUTPUT 

Connect your amp or the audio input of a DAW or a mixer here. 

The ISO output has an input signal which is isolated by means of the LEHLE TRANSFORMER HZ. A balanced or an unbalanced signal is possible, irrespective of the type of signal fed from the input. 

Phase Flip#

The advantages of the LEHLE P-ISO are its compact dimensions, uncomplicated usage and high-quality attributes.

If you’re used to using the LEHLE P-SPLIT III, you might be looking around for the appropriate switch on the LEHLE P-ISO when you need to flip the phase.

But no worries: you will be able to flip the phase at the LEHLE P-ISO with no switch at all.

All you need is a TRS jack you have soldered onto a cable.

You can use this cable at the input socket (1) or at the ISO output (2) so that the LEHLE TRANSFORMER HZ will flip the phase for you.

This is how the modified cable looks like.

Typical Uses: LEHLE P-ISO ...#

as a line isolator - the universal cure for hum loops#

DEVICE CONNECTION

OutputInput effects pedal
InputAmplifier

The LEHLE P-ISO can be used in any scenario to eliminate noise resulting from ground loops or hum. Ground loops occur when units grounded by a protective earth conductor (“PE conductor”) are connected to each other. The protective earth conductor and the ground connection of the audio signal create a loop which will pick up external interference generated, for example, by coils. Such interference will impair the signal. The LEHLE TRANSFORMER HZ included in the LEHLE P-ISO galvanically isolates the ground connection. The hum loop is thus broken at this point.

Both high- and low-impedance signals can be fed, the LEHLE P-ISO has no problems with balanced or unbalanced signals.

HOW TO DO THIS:

  1. Connect the signal source to the input (1) of the LEHLE P-ISO
  2. Connect the ISO socket (2) to the signal input.
  3. Done!

In the above scenario, the LEHLE P-ISO is grounded via the signal source input.

In some cases, it may be a good idea to connect the ground to the other side, in order to eliminate even more interference. To do this, simply swap the input (1) and the ISO output (2).

as an isolator in a stereo setup#

DEVICE CONNECTION

OutputInput effects pedal
InputAmplifier

Background noise can occur often if you connect the stereo outputs of an effects pedal to two amplifiers.

Here again, ground loops occur when units grounded by a protective earth conductor (“PE conductor”) are connected to each other – in this case the two amplifiers.

If you place the LEHLE P-ISO in between one effects pedal output and an amplifier, this connection is isolated but the setup is still stereo.

HOW TO DO THIS:

  1. Connect the first output of the stereo effects pedal directly to the first amplifier.
  2. Connect the second output of the stereo effects pedal to the input of the LEHLE P-ISO (1)
  3. The ISO output (2) needs to be connected to the input of the second amplifier.
  4. Done!

In the above scenario, the LEHLE P-ISO is grounded via the signal source input.

In some cases, it may be a good idea to connect the ground to the other side, in order to eliminate even more interference. To do this, simply swap the input (1) and the ISO output (2).

as a Reamplification Box#

DEVICE CONNECTION

OutputInterface
InputAmplifier

Once you’ve recorded the dry signal, it can be fed through an amplifier during mixing; connecting the amp to the sound card or DAW will almost certainly generate a ground loop, causing undesirable noise. This problem can be effectively eliminated using the LEHLE P-ISO. The built-in LEHLE TRANSFORMER HZ galvanically isolates the ground connections, and functions perfectly with both balanced and unbalanced signals from a sound card or a DAW.

HOW TO DO THIS:

  1. Connect your sound card or DAW to the input socket (1) of the LEHLE P-ISO.
  2. Connect the ISO socket (2) to the input of your amp.
  3. Done!

In the above scenario, the LEHLE P-ISO is grounded via the signal source input.

In some cases, it may be a good idea to connect the ground to the other side, in order to eliminate even more interference. To do this, simply swap the input (1) and the ISO output (2).

Signal Flow Diagram#

Download Manual#

DOWNLOAD MANUAL