ATI MLA400-1 User Manual

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© Copyright 2008, Audio Technologies Inc.

MLA400-800 MMA400-

800

LINE AND MICROPHONE AMPLIFIERS

OPERATING AND MAINTENANCE MANUAL

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DESCRIPTION

Our engineers insist on including this section in all of our instruction
books. We know it is really just an excuse to blow their own horns by telling you
about all the clever things they have done inside your Multiple Amplifier Array. If
they have really been clever, you will never have to even think about what's
inside the box and this whole section will be superfluous.

Multiple Amplifier Arrays provide you with either four or eight identical Line
or Microphone Amplifier channels depending on the model selected. These
channels may be used as individual independent and isolated amplifiers or they
may be combined at internal summing points brought out to the rear connector to
form mixers, summing amplifiers, distribution amplifiers etc.

Multiple Line Amplifier Arrays (MLA) apply balanced or unbalanced line
level input signals directly to a differential input stage with good common mode
rejection and RC bypassing of any RF signals picked up on the inputs. This stage
will accept line levels up to +22dBm (10Vrms) without clipping and has a typical
equivalent input noise (EIN) of only -96dBm thus yielding a 118dB dynamic
range. More to the point, even with line inputs as low as -20dBm, you will
maintain a 76dB S/N ratio. An input impedance greater than 30,000 ohms is high
enough to avoid loading of even IHF (phono jack output) lines. A bi-fet input IC
(LF347) provides fast and symmetrical slew rate performance along with high
loop gain for minimum transient and harmonic distortion generation.

Additional gain of 41dB and improved noise performance for low-level
signals is provided in the Multiple Microphone Amplifier Arrays (MMA). A dual,
low noise IC (OPA2227) is interposed ahead of the differential stage in an
instrumentation amplifier configuration. EIN of -120dBrn allows good S/N
performance with typical microphone input levels. A very high input impedance of
20,000 ohms for balanced inputs avoids all loading effects on the microphone.
Input DC blocking capacitors allow use of external phantom power supplies with
no fear of input overload. MMA inputs will accept levels up to -20dBu. As a
convenience when mixing high and low level inputs into the MMA, removing
jumper wires J3, J6, J9 or J12 will convert the selected channel into a unity gain,
high-level input, and avoid the necessity for external attenuator pads.

An adjustable gain stage follows the input networks in all models. This
stage utilizes a unique circuit arrangement that allows us to provide a smooth, full
range logarithmic gain control in each channel using an inexpensive (but good)
linear cermet potentiometer. This circuit provides an additional 20dB gain at full
clockwise rotation, unity gain in the 12 o'clock position and tapers smoothly to full
off at the full CCW position. Since we actually vary the gain of the stage rather
than attenuating the input to a fixed gain stage, we can use the channel at low
output levels with very little noise penalty. You can easily match channel outputs

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to console medium level inputs (-20dBm) or to drive IHF inputs (single ended at
.10Vrms) without requiring outboard attenuator pads.

A summing junction, isolated from the adjustable gain stage output by a
1K ohm build out resistor, is brought out to the rear connector to allow channel
inputs to be added together and single inputs to drive multiple outputs. Any
channel may be interconnected with any or all other channels. Unused inputs
should have their pots turned to off (full CCW). Each summed channel is
attenuated in proportion to the number of connected channels, e.g. 2 ch = 6dB,
3ch 10dB, 4ch = 12dB, 8ch = 18dB.

The summing junction is also the input terminal of the channel’s output
line driver. The output stage is a balanced driver, which is either transformer or
resistively coupled to the output line. Each channel is programmable for different
output stage gains with a jumper plug connector. The basic stage gain is 6dB
with the plug in the center position; additional gain of 10 or 20dB is selected by
moving the plug. Units are generally shipped set up for +10dB (16dB total stage
gain).

Transformer coupled outputs (-1 models) are recommended when driving
long lines since the low source impedance will minimize high frequency roll off
due to cable capacity and the total primary to secondary isolation prevents AC
power line ground system voltage differentials from adding in with the audio at
the receiving end. Transformer outputs are also best for driving both balanced
and unbalanced lines. The output transformer is a low leakage reactance design
and it is loaded with an RC network to maintain smooth high frequency response
and excellent square wave performance whether it is resistively terminated with
600 ohms or left unloaded.

Active balanced outputs (-2 models) are more economical and are
preferred for short cable runs driving known loads. Avoid driving an active output
into a device with a single ended, unbalanced, one side grounded input since this
condition effectively shorts out the amplifier driving the low output. These inputs,
of which lHF phono jacks are typical, can be driven from an active balanced
output by connecting the load between a HI output terminal and a GND (rather
than HI and LO terminals). Each active output is isolated from the output
terminals by DC blocking capacitors and 150 ohms of build-out resistance. The
build-out resistors are split and bypassed to prevent any RF signals that might be
picked up on an output line from feeding back into the amplifier.

The Multiple Amplifier Arrays operate from an internal bipolar 15VDC
regulated supply. The power supply is designed for minimum susceptibility to
power line transients and conducted RFI using ferrite beads, double capacitive
bypasses and a non-concentric wound semi-toroidal power transformer with a
mu-metal shield.

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APPLICATIONS

The Multiple Amplifier Arrays provide you with four or eight high gain
channels (MMA400, MMA800) or four or eight lower gain channels (MLA400,
IVILA800).

The high gain channels of the MMA are ideal for general microphone to
line amplification and for use as program amplifiers operating from low
impedance, low level console buss levels. A single microphone may be
paralleled into several inputs to make a mike distribution amplifier that can be set
up to drive each output at a different level, each output having its own
independent gain control. Since each input has 20,000-ohm balanced input
impedance, even paralleling one microphone into all eight inputs will not cause
any noticeable loading of the microphone.

A single input channel with its single gain control may feed multiple
outputs by jumping channels together at the summing points available on the
rear connector. All outputs are then adjusted by the single gain control and may
either be set all to the same level or offset in ten dB steps (with the output gain
jumper plugs P1 through N) to drive outputs at approximately -10dBv, 0dBm and
+10dBm for use in a press box application. Unused inputs should have their gain
pots turned off at full CCW rotation to avoid excess noise.

Multiple inputs may be summed to multiple outputs by interconnecting the
rear connector jumpers. You can make an effective and simple mike mixer this
way for pre-set installations such as conference rooms that don't require
continuous adjustment.

Any high gain input of the MMA400 and MMA800 may be converted to
accept line level inputs up to +22dBu by clipping wire PC board jumpers J3, J6,
J9, or J12 to change channels 1, 2, 3 or 4 respectively. This will allow balanced
high level sources and unbalanced IHF sources at -10dBv to be mixed with
mikes or other low level sources.

The Line Input MLA400 and MLA800, with up to 46dB gain available, are
ideal for building up IHF phono plug outputs (-10dBu, high Z) to balanced 600
ohm levels. With four or eight channels available, they are a natural fit for
interfacing small recording consoles into balanced systems. The high impedance
balanced inputs will not load down an IHF output and will provide good
cancellation of any common mode hum that is picked up by the input wiring.
MLAs will also interface from balanced 600 ohm lines to unbalanced, one side
grounded, IHF inputs by connecting the center conductor to the high (or low) side
of the active balanced output with the shield tied to ground.

MLAs are useful for making stereo L+R summing networks, mixing
systems and various types of distribution systems by combining channels with

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the rear panel jumpers. They also make convenient gain blocks and telephone
line interfaces.

INSTALLATION

MOUNTING

Your Multiple Amplifier Array is designed for rack mounting on standard
E.I.A. 1-3/4 inch centers. Each unit dissipates approximately 20 watts and is
ventilated through slots in the rear panel. We have absolutely no idea how many
MMAs you can stack up in a rack before the solder melts, but we will be happy to
sell you enough to find out.

WIRING

Our insurance company insists on three wire grounded plugs. The power
line ground could cause a loop with your studio ground. If you are sure your
studio ground will provide adequate protection to your 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 studio
ground from the chassis.

To allow maximum flexibility of ground in high RF environments, the circuit
board amplifier grounds are isolated from case ground. For normal operation,
you must add a ground jumper from a barrier strip ground terminal to the chassis
ground screw. Failure to ground the circuitry will result in excessive crosstalk,
possible oscillation and increased susceptibility to RF pickup.

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

We have taken heroic measures to keep RF pickup out of your amplifier.
This heroism includes split and bypassed input and output resistor networks,
Faraday shielded output transformers, beaded, bypassed and isolated power
inputs, non-concentric wound power transformers, double ground plane PC
boards and a nice enclosure which will keep rain and snow off the circuit boards.
However, in a difficult broadcast environment, any RF shielding and suppression
system is going to be no better than the ground system into which it is trying to
dump the unwanted RF. If you have a decent ground system and still have RF
problems, give us a call and we will hold a telephone prayer meeting. If you don't
have a ground system, you will still be O.K. as long as you don't turn on your
transmitter.

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Audio inputs and outputs should be connected using the rear panel labels
as a guide. HI outputs are all in phase with each other and are in phase with the
HI inputs. Fanning strips are provided with your unit so that our ears won't start
burning in the middle of the night when you try to wrap wires around those tiny
barrier block screws. The fanning strips can be cut up into individual groups of
terminals, if desired. The fanning strips are Kulka part number 649A22 and
extras are available at exorbitant prices from our Parts and Accessories
Department. Kulka sells them cheaper, but they have a six-month lead-time,
which isn't going to do you any good when you have to be operating by Thursday
and somebody threw out the original strips with the packing material.

CAUTION: Your Multiple Amplifier Array has active drivers for the balanced
outputs if the model number on the rear panel serial number label has a -2 suffix,
e-g, MMA400-2, MLA800-2. (Models with -1 suffixes have transformer-balanced
outputs). Units with active balanced outputs have active drivers for both the HI
and the LO output terminals. DO NOT GROUND EITHER THE HI OR LO
OUTPUT TERMINALS OF ACTIVE BALANCED OUTPUT MODELS. If you are
driving a single ended, unbalanced, one side grounded, IHF, phono jack type
input either high impedance or 600 ohms, it should be connected from either HI
to GND or LO to GND but NOT from HI to LO. Only if you are driving a balanced
load, connect it between HI and LO output terminals. It is not necessary to
terminate an active output driver although placing a 600-ohm terminating resistor
across a hi-Z input at the receiving end will sometimes reduce RF pickup.

Transformer output units may be connected to either grounded or
balanced loads with impunity (wire works better). Transformer outputs prefer to
be terminated in their rated impedance (600 ohms) for flattest response,
however, you can leave these unterminated with only minimal effect since we
provide internal high frequency loading networks.

To further confuse the issue, all MMAs have active balanced INPUTS,
these are NOT the same as active balanced outputs and nothing in the previous
two paragraphs has anything to do with them. Active balanced inputs can be
driven from active or transformer balanced outputs, unbalanced outputs, IHF
phono jacks or practically any other signal source below +22dBm maximum level.
Connect the signal HI to input HI and the source LO (if balanced) or Shield or
Ground (if unbalanced) to the LO input terminal. Unless the source has a
transformer balanced output there should be a ground connection carried
between the source and the MAA ground. DO NOT FLOAT THE LO INPUT;
either connect it to the source or jumper it to ground, otherwise the input stage
gain and frequency response will be affected.

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ADJUSTMENTS

It is sometimes difficult to maintain good noise performance when using a
high output amplifier to drive medium level console inputs (-20dBm) or IHF
(-10dBu, .25V) equipment inputs. You may have found it necessary in the past to
insert attenuator pads to allow the amplifier to operate at a high enough level to
maintain a good signal to noise ratio. The MAA will reduce its already low noise
as you turn down its gain pot and in the lowest output gain position will provide a
comfortable S/N ratio even at -20dBu out. In the absence of high RF levels, you
can distribute levels from 0 to -20dBm, and avoid building, trimming and repairing
all those nasty little attenuator pads.

MAINTENANCE

Power supply voltages are + and - 15VDC nominal.

IC output DC voltages under no signal; shorted input conditions should remain
within .1VDC of ground. Greater deviation is a good sign of IC or circuit
problems.

Five to ten years from now replace all the aluminum electrolytic capacitors.

Keep 250W soldering guns out of the amplifier.

If hit by lightning, replace U1 through U12 and anything else that has turned
black or smells bad.

MODIFICATIONS

Your MAA is wired for 115VAC, 50/60Hz operation unless otherwise
requested at the time of ordering. It can be easily modified for 230VAC operation
by removing the power transformer primary jumpers J17 and J19 and inserting a
jumper in J18

Different types of attachment plugs or line cords may be required for
connection to alternate supply voltages.

If your name is CBS, you can convert the transformer outputs to 150 ohms
line impedance by removing jumpers J13, J14, J15 and J16 and replacing each
with two jumpers from the original jumper terminals to the immediately adjacent
terminals on either side of the original pairs.

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A shaft extender kit (Model SE-8) is available to convert the screwdriver
adjustments to fingertip control. This is a user installed option which requires
removal of the front panel (4 screws), removal of the original screwdriver adjust
shafts by pinching the rear of the shaft and pulling it out of the pot, replacement
of the original shafts with the new ones and finally replacement of the panel (3
screws are enough, forget the one you dropped on the floor). In case you think
that we are giving you the shaft, forget it, these aren't free. Call Mr. Rockefeller in
our Parts and Accessories Department to order.

Output stage gains are set to +6dB, +16dB or +26dB by moving jumper
plugs P1, P2, P3 or P4 from their center position to the +10dB position on the
right or to the +20dB position on the left.

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SPECIFICATIONS

OUTPUT LEVEL: +24dBm into 600 ohm loads. 15Vrms into high

impedance loads.

DISTORTION: Transformer balanced outputs, .25% maximum THD,

30 to 20,000 Hz, +22dBm. Active balanced outputs,
.05% maximum THD, 20 to 20,000 Hz at +22dBm.

FREQUENCY RESPONSE: +/-.25dB, 20 to 20,000 Hz -3dB at 3Hz and 40kHz

typical. Square wave rise time, 6µSec, symmetrical.

NOISE: MMA400/MMA800; E.I.N. = -120dBm maximum with

150 ohm source resistance. MLA400/MLA800; E.I.N. =

-92dBm with 600 ohm source resistance. Both are
measured with 20kHz equivalent square bandwidth. All
hum components are at least 10dB below white noise.

GAIN: MMA400/MMA800: 64, 74 or 84dB. MLA400/MLA800:

22, 32 or 42dB. Each channel's gain is dependent on
output gain jumper plug position.

CMR: 60dB at 60Hz.

CROSSTALK: -70dB maximum at 10kHz.

OUTPUTS: MMA/MLA –1: Transformer Balanced, 60 ohm source

Z. MMA/MLA-2: Active Balanced, 300 ohm source Z,
protected and RF bypassed.

INPUTS: MMA400/MMA800: Balanced 40dB gain, RF bypassed

Instrumentation Amplifier, Zin = 20Kohm. Maximum
input = -20dBu. Gain can be reduced to 0dB by
removing a jumper to accept line levels up to +22dBu.
MLA400/MLA800: Balanced, -2dB, RF bypassed
Differential Amplifier, Zin = 30Kohm, +22dBm
maximum input.

POWER: 115/230 VAC +/-10%, 47 - 63 Hz, 20VA.

DIMENSIONS & WEIGHT: 19" (48cm) W x 1.75" (4.4cm) H x 7.5" (19 cm) D

10 lbs. (4.5kg)

TERMINALS: Rear barrier blocks for all input, output and summing

jumpers. Fanning strips with solder terminals provided
for easy prewiring and servicing.

Specifications are subject to change without notice.

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MODELS AVAILABLE:

MLA400-1 Four Line-to-Line Amplifiers, Transformer Balanced Outputs.

MLA400-2 Four Line-to-Line Amplifiers, Active Balanced Outputs.

MLA800-1 Eight Line-to-Line Amplifiers, Transformer Balanced Outputs.

MLA800-2 Eight Line-to-Line Amplifiers, Active Balanced Outputs.

MMA400-1 Four Microphone-to-Line Amplifiers, Transformer Balanced

Outputs.

MMA400-2 Four Microphone-to-Line Amplifiers, Active Balanced Outputs.

MMA400-1-PH15 MMA400-1 with 15 VDC Phantom Power Option

MMA400-2-PH15 MMA400-2 with 15 VDC Phantom Power Option

MMA400-1-PH48 MMA400-1 with 48 VDC Phantom Power Option

MMA400-2-PH48 MMA400-2 with 48 VDC Phantom Power Option

MMA800-1 Eight Microphone-to-Line Amplifiers, Transformer Balanced

Outputs.

MMA800-2 Eight Microphone-to-Line Amplifiers, Active Balanced

Outputs.

MMA800-1-PH15 MMA800-1 with 15 VDC Phantom Power Option

MMA800-2-PH15 MMA800-2 with 15 VDC Phantom Power Option

MMA800-1-PH48 MMA800-1 with 48 VDC Phantom Power Option

MMA800-2-PH48 MMA800-2 with 48 VDC Phantom Power Option

Other configurations are possible, consult factory for unusual requirements.