ADDAC Systems - 800X High-End Outputs

Inspired by the legacy designs of premium vintage gear, the ADDAC800X behaves like a high-quality DI box and is designed to keep the sound coming from a modular system free from any undesired noisy interferences, ensuring that the outputs reflect what the modular is actually producing. It provides galvanic electrical isolation between the modular system and external sources, preventing impedance mismatch and ground loop induced hum. The ADDAC800X circuit is designed around a unity 1:1 type nickel core Hammond Audio Transformer from the 140UEX series (equivalent to Jensen audio transformers).

Operating in the 20Hz to 20kHz range and providing exceptional shielding from external sources, this impedance matching transformer provides the ADDAC800X with two fully balanced high-end outputs via XLR connectors.

The Importance of Using Audio Transformers

Applying a transformer balanced output isolation has many advantages over other less expensive methods for dealing with ground loop issues. This method provides the chance to set a very simple and clean circuit in which the signal transfer process develops smoothly and hum-free. The transformer is a device that performs both signal balancing and high-to-low (or vice-versa) impedance conversion, while rejecting stray 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, the ADDAC800X presents a most accurate electrical isolation between its input and output. The 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 the ADDAC800X from any other device, preventing hum problems coming from an external ground.

USAGE:

LEFT IN will output sound to both channels. Through RIGHT IN, signal will only find its way to OUT 2 (if the LEFT/RIGHT toggle is lifted up, RIGHT IN will be ignored and LEFT IN will be present in both OUTs). With both INs connected, there will be two separate outputs (LEFT IN → OUT 1 & RIGHT IN → OUT 2). However, lifting up the LEFT/RIGHT toggle will also ignore RIGHT IN, and LEFT IN will feed both OUTs.

Each transformer isolated output section has its signal overload warning LED and two dedicated toggle switches: one that works as a simple amplifier/attenuator pad to +6dB/−10dB respectively, and a LIFT/FLOAT/GND toggle. This last one is a 3-way selector that allows choosing between lift, ground, or floating ground (toggle's middle position) to be taken as reference for the ground point. In the LIFT position, the module circuit will be lifted to ground through a 100R resistor and a 10nF capacitor, and pin 1 of the XLR connection will act as the ground point. Choosing GROUND will put ground to be shared between inputs and outputs. Floating ground will leave input and output grounds completely separate from each other. Any of these three positions may be the best option for avoiding ground loops or any other undesired interference occurring between a modular system and the sound system it's connected to. Try out which option works best in a given situation.

A headphones amplifier (with volume knob) connection is available for quietly working with a modular system or pre-listening sounds before making them public in a live situation. This section features an OPA2134 High-Performance Audio Operational Amplifier. This device presents the ideal characteristics for use with a headphones set, including ultra-low distortion and low noise fully specified for audio applications, in combination with high-output drive capability and excellent DC performance that altogether allow for high dynamic headroom and superior sound quality.