ATI DA1000 User Manual

DA1000

DISTRIBUTION AMPLIFIER

OPERATING AND MAINTENANCE MANUAL

© Copyright 2012, DaySequerra Corp.

Day Sequerra │ 154 Cooper Rd. #902 │ W. Berlin, NJ 08091 │ Voice 856-719-9900 │ [e-mail] │ www.atiaudio.com

DESCRIPTION

The ICs developed primarily for the instrumentation market had many shortcomings
when used in high quality audio applications. The lack of audio related specifications,
crossover distortion, high noise for low source impedances, limited output capability and
limited gain bandwidth product forced many compromises when used in audio systems.
High ratio input transformers, output boost stages and multiple stage designs were all
used to compensate for op amp deficiencies and in turn added additional response and
distortion problems of their own.

Walter Jung, in a definitive series of articles, analyzed and defined slew rate induced
distortion mechanisms, tested many commonly available ICs and correlated various
distortion tests with subjective (listening) criteria. A very significant result of his efforts
was the identification of an IC originally developed for the European professional audio
market which has almost ideal characteristics for audio use and in particular provides a
high slew rate capability of 13 volts/microsecond, virtually eliminating slew induced
Transient Intermodulation Distortion. By contrast the old standard 741-op amp has a slew
rate of only .6V/microsecond.

This op amp is now available from several U.S. Manufacturers in single and dual
versions and forms the basis for our designs. This chip incorporates an input stage
designed for excellent noise performance with a wide range of source impedances, thus
eliminating the necessity for input step up transformers. An output stage capable of
driving 600 ohm loads directly to +22dBm with total freedom from crossover distortion,
high inherent linearity, 100dB open loop gain and 50 MHz gain bandwidth product make
this an ideal device for highest quality audio. The absence of Transient Intermodulation
Distortion may be detected by the smooth effortless high frequency output capability, the
absence of the harsh, raspy sound typical of IC amplifiers driven to full output at high
frequencies and the freedom from increasing harmonic distortion vs. frequency. As used,
a minimum of 40dB of loop gain is available for 100:1 distortion reduction even at
20kHz. All program audio stages in the Distribution Amplifiers use this unique device in
its dual version (NE5533).

INPUT
Input audio feeds a unity gain balanced differential input buffer stage (Al), which

presents 30,000-ohm bridging impedance to the source. The inputs are protected from
over voltage inputs by clipping diodes (CR4-CR7). Dual bypass capacitors (C7, C29 and
C8, C39) protect the inputs against common mode RFI pickup. A balance potentiometer
(R9) allows setting a precise null for common mode hum inputs.

SIGNAL PRESENT INDICATOR
The second half of Al monitors the voltage at the output of the input buffer IC. The green

Signal Present LED on the front panel will light for audio inputs over -30dBm. The LED
will normally flicker with applied program material to tell you that all is well. (Happiness
is a green LED).

Day Sequerra │ 154 Cooper Rd. #902 │ W. Berlin, NJ 08091 │ Voice 856-719-9900 │ [e-mail] │ www.atiaudio.com

OUTPUTS
Audio from the input buffer is AC coupled to the front panel level adjusts potentiometer.

This control adjusts the level of all outputs. If you are afflicted with lurking knob
twiddlers, the knob can be removed leaving a somewhat less inviting screwdriver
adjustment. If removing the knob doesn't cure the problem, put your DA out of reach by
sticking it to the ceiling using the supplied suction cup feet.

The pot output is applied to the non-inverting input of the HI (in-phase) output stage
driver IC (A2-1). The IC supplies the first 10 mA of output current directly and then the
complementary Class B output booster transistors (Q1 and Q2) take over. The unique,
wide bandwidth, high slew rate circuit design provides effective class AB operation with
minimal crossover distortion from a power output stage operating true Class B with zero
quiescent power dissipation.

The HI output bus is applied to the inverting input of A2-2 in a unity gain, phase
inverting configuration and boosted by Q3 and Q4 to form the LO output bus.

The HI and LO output buses are split into nine individual outputs (eight rear and one
front panel jack) through 150 ohm build out resistances. All outputs will tolerate short
circuits across the output or to ground without damage. Up to two outputs can be shorted
with no significant reduction in headroom. Needless to say, this is NOT the
recommended mode of operation - do not drive single ended (one side grounded) loads
from both HI and LO outputs together. Drive single ended loads from either the HI or LO
outputs to ground. Up to 18 single ended 600-ohm output loads may be simultaneously
driven.

The build-out resistors are split and heavily bypassed to prevent RIF pickup on the output
lines from affecting operation of the DA. These bypasses will place a very heavy load on
the outputs under sustained sine wave operation above 20kHz and such operation may
over dissipate the 47 ohm build-out resistors - don't do it!

OUTPUT CLIPPING INDICATOR
The differential input voltage of H1 output driver IC (A2-1) is monitored by A3. The

differential voltage is under a few millivolts under linear operation, however, if the
output is driven to clipping, the differential voltage rapidly increases and is amplified to
light the yellow OUTPUT CLIPPING LED. Conserve power - try not to light the yellow
LED.

HEADPHONE OUTPUT
The front panel headphone jack provides a ninth output with its own set of build out

resistors. The phone jack is a convenient metering point, an auxiliary output or
headphone output. The jack is wired primarily to drive stereo headphones with an inphase
mono signal consequently tip (red) and ring (blue) are wired together and to the HI output

Day Sequerra │ 154 Cooper Rd. #902 │ W. Berlin, NJ 08091 │ Voice 856-719-9900 │ [e-mail] │ www.atiaudio.com

and the sleeve connection (white) is wired to the LO output. To use a standard tip ring
sleeve patchcord output, rewire the jack terminals by removing the blue wire from the
ring terminal moving the white wire to the ring connection (and grounding the sleeve
terminal to the top shield foil of the P.C. board.)

POWER SUPPLY
Your power supply incorporates a couple of unique regulating devices called zener

diodes. In contrast to most fancy IC regulators, these devices will live through most line
transients and simultaneously protect your expensive circuitry. As further insurance, a
varistor suppresser is placed across the power transformer secondary.

INSTALLATION
MOUNTING

Your DA1000 may be desk mounted on its non-slip suction cup.
Rack mount system 21075-501 mounts two units in one rack.

WIRING
There are three wire grounded plugs. The third wire ground can cause a ground loop with

your station ground. If you are sure your station ground will provide adequate protection
to personnel in case of an AC line short to chassis, a 3 to 2 AC adapter can be used to
isolate the power line ground. We recommend that the adapter be removed and the power
line ground reconnected prior to any service work requiring removal of the station ground
from the chassis.

The four inch silver bearing copper strap, which you are, of course, using for your station
ground is not going to fit around the #6 chassis ground screw on the rear panel. Run the
strap to within a few inches of the chassis jump to the chassis ground with shield braid.

Audio inputs and outputs should be connected using the rear panel labels as a guide. Hl
outputs are all in phase with each other and in phase with the Hl inputs. Fanning strips are
provided so that our ears won't be burning in the middle of the night while you are trying
to wrap wires around tiny barrier strip screws. The fanning strips are Kulka part number
649A22 and extras are available from our Parts and Accessories Department.

To allow maximum flexibility in grounding in high RF environments, the circuit grounds
are isolated from case ground. For normal operation, add a ground jumper from the
barrier strip ground terminal closest to the inputs to the chassis ground screw.

CAUTION: Balanced differential output has active drivers for both HI and LO output
terminals. DO NOT GROUND either HI or LO terminals. To drive an unbalanced (one
side grounded) load, connect it between HI and GND terminals and let the LO terminal
float. Two separate 600 ohm unbalanced loads can be driven from each output without

Day Sequerra │ 154 Cooper Rd. #902 │ W. Berlin, NJ 08091 │ Voice 856-719-9900 │ [e-mail] │ www.atiaudio.com

interaction by connecting one between HI and GND and the other between LO and GND.
The two loads thus driven will be out of phase with each other.

MAINTENANCE NOTES
Power supply voltages are + and - 20 VDC nominal. Maximum allowable voltages are

+/- 22 VDC (limited by IC). If zeners are replaced, remove ICs and check output voltage
before plugging ICs back into the circuit. Remove power when inserting or removing
ICs.

IC output DC voltages (no signal conditions) should measure 0VDC +/- .5 VDC.
Significant deviation indicates IC or circuit problem. Measurable DC difference between
+/- amplifier inputs (other than due to meter loading) indicates IC failure.

If hit by lightning, replace Al through A3.

MODIFICATIONS

230 VAC Operation

Your DA1000 is wired for 115 VAC 50/60 Hz operations unless otherwise requested at
the time of ordering. It can be modified for 230 VAC use by removing the power
transformer primary jumpers J1 and J3 and inserting a jumper in the J2 holes.

GAIN

To increase gain by 10dB, change R13 to 680 ohms, and increase C15 to 68 uF.

Day Sequerra │ 154 Cooper Rd. #902 │ W. Berlin, NJ 08091 │ Voice 856-719-9900 │ [e-mail] │ www.atiaudio.com

SPECIFICATIONS

OUTPUT CLIPPING LEVEL
DISTORTION @ 24dBm output and input levels to

+24dBm

+24dBm / 600 ohms

.2% maximum THD, 20Hz to 20kHz

FREQUENCY RESPONSE +/- .25dB, 20 to 20000 Hz.

-3dB at 100 kHz

OUTPUT NOISE -70dBm maximum

20kHz measurement bandwidth

IMPEDANCE FULL GAIN 600-ohm source

HUM REJECTION 80dB for common mode hum

INPUT IMPEDANCE Balanced differential inputs, 30,000

ohms bridging +24dBm maximum input
level.

GAIN 26dB, front panel adjustable

OUTPUT ISOLATION 70dB minimum at 1 kHz, any output to

any other output. Unit will tolerate up to
two shorted outputs with no reduction in
headroom.

POWER 115 / 230 VAC +1- 10%, 47-63 Hz.

SIZE 8-1/2" W x 1-3/4" H x 7" D, 2-1/2 lbs.

MOUNTING Suction feet for non-slip desk mounting

Rack mount system 21075-501 mounts
two units in one rack.

Day Sequerra │ 154 Cooper Rd. #902 │ W. Berlin, NJ 08091 │ Voice 856-719-9900 │ [e-mail] │ www.atiaudio.com