Inspired by the legacy designs of premium vintage gear, the ADDAC800X behaves like a high-quality DI box and is all about keeping the sound coming from your Modular free from any undesired noisy interferences, making sure that what you’re getting from your outputs is what your Modular 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 800X 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 20 Hz to 20 KHz range and providing exceptional shielding from external sources, this impedance matching transformer provides the 800X with two fully balanced high-end outputs (via XLR connectors).
The importance of using Audio Transformers
Applying a transformer balanced output 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 clean circuit 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, the ADDAC 800X 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 the 800X from any other device, preventing hum problems coming from an outsider ground.
LEFT IN will output sound to both channels.
Through RIGHT IN, signal will only find its way on 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 you’ll have two separate outputs (LEFT IN -> OUT 1 & RIGHT IN -> OUT2). However, lifting up the LEFT/RIGHT toggle you’ll also find RIGHT IN ignored and LEFT IN will fed 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 lets you choose 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 ins and outs grounds completely apart from each other. 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 sound system you’re plugging it into. Try out which one of this options will work the best in a given situation.
An HEADPHONES AMPLIFIER (with VOLUME knob) connection is available for quietly working with your modular or pre-listen your sounds before making them public matter in a live situation. This section features an OPA2134 High-Performance Audio Operational Amplifier. This device presents the ideal characteristics for use with an headphones set, like 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 really superior sound quality.
. Bus Board Cable: 8 × 2 IDC (Doepfer style) connector