Here's what Lehle say about the Little Dual
The Lehle Little Dual is the Lehle Dual SGoS's little sister, a maximum signal-fidelity amp switcher for two amps. Both amps are activated simultaneously using the left footswitch, while the right is used to switch back and forth between them. High-intensity LEDs make it easy to read off switching state A or B, or A and B, even under high-power spots.
The centerpiece of the Lehle Little Dual is its high-end Lehle LTHZ transformer, which electrically isolates output A from output B, making history of hum loops - permanently! The Lehle Little Dual features a gold-plated-contact phase inverter and a gold-plated-contact ground switch. The two inputs can also be routed in stereo to outputs A and B, if you use the stereo signal of an effect unit as the input, for example. This also makes it possible to route instruments equipped with two pick-ups, including many acoustic and hybrid guitars, and also double basses, via two amplifier systems - with no complications. These systems can be operated either in alternation or in parallel - without hum, and without sound losses, needless to say! The Lehle Little Dual - small, but so utterly effective!
Q: What is galvanic isolation?
A: Background noise, generated by ground loops, occurs again and again when two electronic devices are connected to each other, and the Lehle Little Dual provides a simple but extremely effective remedy when installed between the two units. The two devices are electrically isolated when the `A´ output is used, eliminating this background noise.
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 LTHZ transformer included in the Lehle Little Dual electrically isolates the ground connection. The hum loop is thus broken at this point.
Q: Does the galvanic isolation color my sound?
A: No, neither sound nor dynamics will be altered, the signal is passing the switcher without any loss in strength or frequency. We use our self-developed Lehle LTHZ transformers for this, the selection of high quality components guarantees a rich sound throughout the full frequency range.
Q: Is the signal suitable for a mixer/recorder? I would like to play thru my effects and simultaneously record a dry signal for later re-amping.
A: No problem, just make sure the mixer/recorder features a HiZ input, otherwise the instrument will sound flat and lifeless. Optional the output signal can be balanced by using a TRS to XLR connection.
Q: Can I use the Little Dual for acoustic guitars with onboard preamp?
A: Absolutely! The switcher works passively and can handle all kinds of audio signals without distortion or loss, for weaker piezo signals as well as stronger line level signals.
Q: Can the Little Dual/Dual SGoS be used as DI box since it has 14" sockets?
A: Yes, you get a balanced or unbalanced (mono-) signal from transformer-isolated output A when using a stereo (TRS) cable.
Q: Does it affect the sound and dynamics of my instrument when I use the Little Dual without power supply? In the manual it says the power is only for the LEDs.
A: It makes no difference since the switcher works passive. Power is indeed only for the LEDs, neither dynamics nor sound will be altered in any way.