ATI Technologies DDA SERIES Operating instructions

Audio Technologies Inc.
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DDA & D S A S E RI E S
AES/EBU DIGITAL AUD I O
DISTRIBUTION AMPL I F I ERS
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OPERATING AND MAINTENANCE MANUAL
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© Copyright 2008, Audio Technologies I n c.

Audio Technologies Inc.
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audio.com
DESCRIPTION
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The DDA Series of Digital Audio Distribution Amplifiers are designed to
regenerate, isolate and distribute digital audio data formatted in accordance with
specifications AES3-1992 and IEC 958. This is commonly called AES/EBU
formatting.
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The DSA Series operates much the same as the DDA Series; however, the DSA
Series does not include the full featured display front panel and does not provide
re-clocking of the digital input signal. The non-reclocking feature is essential
when distributing Dolby E encoded AES signals and other clocked signals that
should not be re-clocked.
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DDAxxx-XLR and DSAxxx-XLR models use XLR connectors and operate from
and drive a 110-ohm balanced shielded twisted pair distribution system per
AES3-1992.
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DDAxxx-BNC and DSAxxx-BNC models use BNC connectors and operate from
and drive single-ended 75-ohm coaxial cable per AES-3id-1995 and are
designed to integrate easily into video facilities.
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S/PDIF (consumer) formatted digital audio data differs primarily in the use of
consumer type "RCA" audio connectors in an unbalanced 75 ohm system and
can be handled by a DDAxxx-BNC with use of an RCA to BNC input cable.
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S/PDIF digital audio can be connected directly to a DSA106-RCA unit.
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FEATURES
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• Accepts sample rates from 27 to 96kHz
• Displays standard sample rates of 32, 44.1, 48, 88.2, 96 kHz (DDA only)
• Status and error LEDs show clock lock and data validity (DDA only)
• Adjustable input equalizers compensate for very long cable runs (DDA only)
• Data is relocked and regenerated before low-jitter transmission (DDA only)
• Loop thru transformer balanced and isolated inputs
• Switchable input termination resistors
• Individual, transformer balanced and isolated 110 ohm XLR outputs (-XLR only)
• Individual isolated 75-ohm BNC outputs (-BNC only)
• Single or dual inputs
• Up to 12 XLR or 24 BNC outputs
• Quiet, internal linear power supplies
• Attractive, 1RU package

Audio Technologies Inc.
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DESCRIPTION
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INPUTS
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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 DIP switches S1a (S1b). Inputs should always be terminated
unless they are looped thru to another device or DDA input. The last device or
input should always terminate the line.
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INPUT EQUALIZERS
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The input signals feed cable equalizer circuits U3 (U4) and associated
components. Input equalization should only be necessary for extremely long
input cable lengths and should only be used if proven to be necessary. The
equalizers are adjustable with front panel multi-turn trimpots R63 (R66) so that
only the minimum amount of boost required to compensate for excess cable roll-
off can be added without over-equalization, which can degrade noise margins.
See adjustment instructions in the INSTALLATION section. If input equalization
is not required and you want to protect yourself from random control diddlers, you
may disable the equalizers by removing jumpers E4 (E5).
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RECEIVERS
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(Note that DSA Series units do not re-clock and provide no front panel status
information. The following section applies to DDA Series units only.)
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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.
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Frame sync (FSYNC), Serial Clock (SCK), Serial audio data (SDATA), Channel
status (C), User channel data (U), and data validity information (VERF) are
passed directly to the transmitter IC for reformatting into the output data stream.
VERF is an OR’ing of the validity information from the incoming data (V) with an
internal error flag (ERF) that detects serious transmission errors such as parity
errors, bi-phase coding violations and an out-of-lock PLL receiver. VERF then
becomes the transmitted validity bit (V) and can be used by downstream error
correction devices to interpolate through errors.
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Received frequency information is encoded on U8 (U17) pins F0, F1 and F2 and
is decoded by U14 (U19) into two BCD digits for display. Error information is
encoded on pins E0, E1 and E2. It is decoded by 3 to 8 line decoder U20 (U22)
and sent to the front panel display LEDs.

Audio Technologies Inc.
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DISPLAYS
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(Note that DSA Series units do not re-clock and provide no front panel status
information. The following section applies to DDA Series units only.)
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The two most significant digits of the sample rate are decoded by U1 AND U4
and displayed if the sample rate is within +/- 4% of a standard rate. Since only
two digits are displayed, readouts of 32, 44, 48, 88 and 96 correspond to actual
sampling rates within four percent of 32.0, 44.1, 48.0, 88.2 and 96kHz. The
displays are blanked if the detected frequency is out of range.
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Data and transmission errors are displayed in priority order of no lock, BI-PHASE
Coding errors, PARITY errors and CRC errors. The no-lock signal is inverted and
lights when the clock recovery PLL is in LOCK. The VALIDITY indicator shows
that the previous received sample was valid when transmitted from the source
device. NO ERROR is the absence of any of the other errors and is good. The
SET indicator, used to tune the equalizer adjustment, lights when the received
data eye opening is greater than half a bit period and the recovered clock is
within range.
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TRANSMITTERS
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The Frame sync (FSYNC), Serial Clock (SCK), Serial audio data (SDATA),
Channel status (C), User channel data (U), and data Validity information (VERF)
are passed directly to the transmitters U9 (U18) for reformatting into the
AES/EBU output data stream TXPA (TXPB). The transmitters are Crystal
Semiconductor CS8404A devices capable of operation from 27 to 96kHz
equivalent sample rates. The transmitters operate in a transparent mode, which
allows the transmitter block structure (Channel Status, User and Validity bits) to
be slaved to the block structure of the receiver. In the transparent mode the
propagation delay of data through the CS8404A is set so that the total
propagation delay from the receiver inputs to the transmitter outputs is exactly
three sample intervals, which is less than 100 microseconds even at the lowest
sample rate.

Audio Technologies Inc.
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OUTPUT DRIVERS
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DDAxxx-XLR and DSAxxx-XLR units use the balanced, 110-ohm, transformer
coupled outputs and XLR type connectors shown on the referenced schematics.
DDAxxx-BNC and DSAxxx-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 2Vp-p. 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.
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REFERENCE OSCILLATORS AND POWER SUPPLIES
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U10 generates a 6 MHz reference frequency input to U8 (U17) for determining
the incoming frame (sample) rate. The oscillator is counted down in U11, 12, 15
and 16 to provide a synchronized display reset pulse every 3 seconds. U21
generates a precision 2.5VDC reference for the equalizer circuit. 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.
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INSTALLATION
LOCATION
To avoid addition of jitter (timing variations) to the digital bitstream, which could
cause noise and distortion in the recovered audio, avoid locating the DDA or
DSA in close proximity to a high energy, high frequency switching type power
supply or a power amplifier that utilizes a switching supply. If possible, do not
power both devices from the same AC power line.
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Expensive components start to die at internal temperatures above 70 ° C (158 ° F) .
We recommend that you maintain rack temperatures below 50 ° C (122 ° F) to
prevent excessive internal temperature buildup. This is another good reason not
to mount the DDA or DSA directly above that 500W power amplifier. Don’t force
the DDA to support the weight of 28 coax or 16 XLR cables (especially when you
drop that 500W power amplifier on the cable bundle), support the cables.

Audio Technologies Inc.
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POWER
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If it is necessary to convert a unit wired for 115VAC to 230VAC operation, unplug
the unit from the power source, remove the four cover mounting screws and
locate the E1 jumpers next to the power transformer. Clip the jumpers 1-2 and 3-
4 (don’t unsolder), jumper from 2-3 carefully soldering together the free ends of
2-3 previously clipped. This procedure is recommended to avoid soldering
damage to the multi-layer PC board.
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WIRING
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XLR types require special controlled impedance, 110 ohm, low loss, foil shielded,
twisted pair cables. Standard audio cable is not recommended except for runs of
only a few feet. Belden and most other cable manufacturers offer special digital
audio cabling for this application. With equalization, cable runs of 300 meters
(about 1000 feet) should be achievable. BNC types use 75-ohm coax (RG59).
Select a cable for losses less than 20dB at 12MHz (for data rates up to 96kHz) at
the maximum distance you require. Runs up to 1000 meters should be readily
achievable with low loss coax.
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INPUT CABLE EQUALIZATION
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If there is an unusually long (more than a few hundred feet) cable connection
between a particular AES/EBU data source and the DDA or DSA, it may be
necessary to equalize the cable response. Equalization would be indicated if it is
not possible to lock onto a known good signal source and obtain a stable reading
of the DDA input sample rate as evidenced by the front panel indicators.
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(The following procedure uses the front panel displays of the DDA to verify
correct operation. Note that DSA units have no front panel display; therefore,
Input Cable Equalization adjustment should be performed with a known-good
AES tester connected to any of the DSA unit’s outputs.)
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1. Apply a known good AES/EBU digital signal with sample rate of 96, 88.2, 48,
44.1, or 32 kHz to the source end of the cable. (You can validate the source by
temporarily co-locating the DDA with the signal source, connecting them together
with a short cable and noting that all red LEDs are off, all green LEDs are on and
the correct sample rate is steadily displayed.)
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2. The factory default setting for the front panel equalizer control(s) is fully
counterclockwise. With a small screwdriver, slowly turn it clockwise, pausing after
each half turn for three seconds to allow the displays to update. Note the first
position at which all red LEDs are off, all green LEDs are on and the sample rate
is displayed steadily.
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3. Continue to turn the control clockwise, counting turns, until the conditions of 2
above are no longer obtained.
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4. Turn the control counterclockwise by half the number of turns counted in 3.
above. This is the optimum setting for the installed cable length and sample rate.

Audio Technologies Inc.
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SPECIFICATIONS
INPUTS
Connectors: XLR female or BNC, DC isolated from chassis.
Input connector pairs paralleled for loop-thru.
Level: 200mVp-p minimum
Impedance: Transformer isolated, capacitor coupled, balanced and
floating, XLR inputs 110 ohms, and BNC and RCA inputs 75
ohms.
Terminating resistors may be switched in or out on rear
panel.
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Cable Length: 300m of 110-ohm cable, 1000 m of 75 ohm coax (with
equalizer)
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Equalizer: Multi-turn panel control, adjust using DSA panel indicators
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Sample Rates: Accepts 27kHz to >100kHz
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DDA Clock: Regenerated from input signal with dual-mode PLL Clock
Jitter <3nanoseconds peak-to-peak at 96kHz sample rate
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DSA Clock: Non-regenerated. Input clock is passed directly to outputs.
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OUTPUTS
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Connectors: XLR male, 6 or 12; BNC chassis mount, 12 or 24
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Levels: XLR, 4Vp-p loaded at 110 ohms. BNC, 2Vp-p loaded at 75
ohms, RCA, 0.5Vp-p loaded at 75 ohms
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Impedances: XLR: 110 ohms, balanced, transformer isolated and
capacitor coupled
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BNC: 75 ohms, unbalanced, capacitor coupled
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Output Jitter: <3 nanoseconds peak to peak at 96kHz sample rate
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Output Delay: Three frames (sample intervals) at the sample rate

Audio Technologies Inc.
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INDICATORS (DDA only)
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Sample Rate: Numeric readout of first two digits of 32, 44.1, 48, 88.2,
96kHz rates if within +/-4%. Out of range blanks display
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Received Signal: Status: NO ERROR, LOCK, VALIDITY, and all Green for
normal operation
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Error: PARITY, CRC, BIPHASE, normally OFF, Red for error
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Cable Equalizer: SET indicator, lit Green for normal operation
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Power: Lit RED for ON
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POWER Internal supply, 115/230VAC+/-10%, 50/60Hz, 10VA,
IEC320 3 pin connector.
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SIZE 1 RU, 19”(48.3cm) W X 1 ¾”(4.5cm) H X 7”(19.1cm) D
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WEIGHT 10lbs (4kg)
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MODELS: DDA106-XLR (1X6)
DDA112-BNC (1X12)
DDA112-XLR (1X12)
DDA124-BNC (1X24)
DDA212-XLR (Dual 1X6)
DDA224-BNC (Dual 1X12)
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DSA106-BNC (1X6)
DSA106-XLR (1X6)
DSA112-BNC (1X12)
DSA112-XLR (1X12)
DSA124-BNC (1X24)
DSA212-XLR (Dual 1X6)
DSA224-BNC (Dual 1X12)