ADDAC711 is a dual channel Isolated DI box and is all about keeping the sound coming into your Modular free from any undesired noisy interferences, making sure that what you're getting from your inputs is what your external hardware is actually producing. It provides galvanic electrical isolation between the Modular system and external sources preventing impedance mismatch and ground loop induced hum. ADDAC's 711 circuit is designed around a unity 1:1 type Low-cost Audio Transformer operating in the 20 Hz to 20 KHz range, this impedance matching transformer provides two fully balanced outputs (via XLR connectors).

There are two independent channels on the module with:
Audio Output
Signal overload warning led
LIFT / FLOAT / GND toggle switch
Gain control
XLR Input

The LIFT / FLOAT / GND 3-way switch lets you choose between lift, ground or floating ground. In the LIFT position (left) the module circuit will be "lifted" to ground through a 100R resistor and a 10nF capacitor. In the FLOAT position (middle) Ground will not be shared leaving ins and outs grounds completely apart from each other fully isolating both signals.
In the GND position Ground will be shared between inputs and outputs, here no isolation is used. Any of these three positions may be the best form of avoiding ground loops or any other undesired interference occurring between your modular and the external hardware. Try out which one of these options will work best in any given situation.

The importance of using Audio Transformers

Applying a transformer balanced input isolation has lots of advantages over other less expensive ways for dealing with ground loop issues. This method provides the chance to set a very simple and cleancircuit in which the signal transfer process develops smoothly and humming free. The transformer is a device that performs both signal balancing and high-to-low (or vice-versa) impedance conversion, while rejecting straggled DC voltage and Radio Frequency Interference from signal passing through a magnetic bridge. In a transformer, two (or more) coils (called windings) of insulated wire wound around a magnetic metal core allow for its input(s) and output(s) not to be physically connected together. When an AC signal passes through the input winding (the primary), a perfectly related AC signal appears on the output winding (the secondary). This way, by the fact that signal flows via inductive coupling between the two windings of the transformer, this module presents a most accurate electrical isolation between its input and output. A same number of windings on each coil guarantees that there's no gain loss when audio signal passes from the primary to the secondary windings. Furthermore, since these two windings are insulated from each other, the transformer will electrically isolate ADDAC711 from any other device, preventing hum problems coming from an outsider ground. Being a low-cost transformer the frequency response curve is not completely linear, still the -0.2dB
attenuation at 50Hz feels negligible.