Audio Technologies Inc. DXA224-BNC
Distribution Amp Dual 1x12 AES/EBU, BNC

• Accepts sample rates from 27 to 96kHz.

• Loop thru transformer balanced and isolated inputs.

• Switchable input termination resistors.

• Individual, transformer balanced and isolated 110 ohm XLR outputs.

• Individual isolated 75-ohm BNC outputs.

• Single or dual inputs.

• Up to 12 XLR or 24 BNC outputs.

• Quiet, internal linear power supplies.

• Attractive, one rack unit package.

Incoming AES/EBU formatted digital audio data is applied to input transformers T8 (T9 for second input channel of dual unit). Both XLR and BNC inputs are balanced and DC isolated from ground. Input blocking capacitors C22 (C24) prevent accidental DC inputs from saturating (and perhaps damaging) the input transformers. Input termination resistors R25 (R26) at 75 ohms for BNC (and SP/DIF) inputs or 110 ohms for XLR inputs can be switched in or out of the circuit with rear panel DIPswitches S1a (S1b). Inputs should always be terminated unless they are looped thru to another device or DXA input. The last device or input should always terminate the line.

The equalized AES/EBU data stream is applied to the receiver circuit U8 (U17) that is a Crystal Semiconductor CS8414 96kHz Digital Audio Receiver IC. The CS8414 receives the data, recovers the clock and synchronization signals and separates the audio and digital data. The audio data may be 16 to 24 bits at sample rates from 27 to 96 kHz.

DXAxxx-XLR use the balanced, 110-ohm, transformer coupled outputs and XLR type connectors shown on the referenced schematics. DXAxxx-BNC units use the alternative 75-ohm unbalanced outputs to BNC coax connectors shown on the same schematics. The XLR outputs are in full compliance with specification AES3-1992 and the BNC outputs are in accordance with the recommendations of AES-3id-1995. RS-422 differential line drivers U1 and U2 (U5 and U6) provide a balanced drive for XLR outputs of 8Vp-p, open circuit through 110-ohm source resistance to yield 4Vp-p when loaded by a 110-ohm load. XLR outputs are transformer coupled for ground isolation. Each side of the differential line driver output is used to separately drive a 75-ohm capacitor coupled BNC output. Each BNC output provides 4Vp-p open circuit thru 75 ohms for a loaded output of 2Vpp.

Although the two sides of a differential line driver are out of phase with each other there is no phase difference in the recovered audio since the AES/EBU digital data is defined only by the presence or absence of transitions. It makes no difference whether those transitions are hi to low or low to hi.

U7 and U13 provide regulated and quiet +/-5VDC for all circuits. Power transformer primary windings are paralleled for 115VAC or wired in series for 230VAC. Jumpers E1 allows field modification if necessary.