General Description
The MA 3 is a three-channel
amplifier designed to operate reliably in commercial environments. The
MA 3 was specifically designed for use with:
- Paging
- Foreground Music
- Background Music Distribution
The
MA 3 uses a conventional linear power supply with toroidal transformer.
This configuration minimizes the emissions associated with switching
supplies and noisier transformer designs. The power supply features
independent secondary supplies for each channel, minimizing load
regulation interaction and crosstalk.
Thermal management is
accomplished with a sealed heat- tunnel design incorporating low
velocity forced air and large aperture openings. This design minimizes
the noise usually associated with forced air cooling and eliminates the
need for an air filter. Forced air cooling allows the amplifier to
operate reliably in harsh environments and avoid the buildup of heat in
unventilated racks associated with passive convection cooling.
The
combination of a solid, conservative power supply and forced-air
cooling allows the MA 3 to simultaneously deliver 40 watts of
continuous average power into 8 ohms and 60 watts into 4 ohms.
SPiKe¢ē*
dynamic protection circuitry completely safeguards each channel against
over-voltage, under-voltage, overloads, transients from inductive
loads, thermal runaway and instantaneous temperature peaks. Biasing is
not allowed to occur when an under-voltage condition exists, reducing
turn on and turn off transients.
Fast-response limiters allow
the MA 3 to tolerate up to 20 dB of overdrive into 8 and 4 ohm loads
while holding THD below 1%. This means no loss of speech
intelligibility or harsh clipping. This feature greatly increases the
dynamic range of the system without external limiters.
Peak-responding,
load-adaptive meters accurately indicate the remaining headroom. The
meters are helpful in setting system levels and indicating signal
compression.
Balanced inputs with Euroblock connectors are
provided. Euroblock output connectors accept up to 12 gauge wire. Rear
panel Level controls allow amplifier sensitivity adjustment. Internally
selectable 80 Hz highpass filters offer protection against over
excursion of small bookshelf speakers and saturation of distribution
transformers at low frequencies.
Features
Built to be driven hard
The
MA 3 Amplifier drives all three channels at the continuous average
rated power, indefinitely. It is specifically designed to operate in
demanding commercial applications. Very low emissions allow the
Amplifier to operate in close proximity to signal processing equipment
without causing excessive interference. The CP 52, CP 64 and DA 26 may
all operate next to the MA 3 in a rack. The high efficiency "heat
tunnel" design allows the Amplifier to process severely compressed
signals reliably even when installed in a rack with elevated ambient
temperatures. Forced air cooling keeps heat away from other equipment.
You won't hear other Zones
The
MA 3 is designed to deliver foreground music, background music and
paging signals to three different Zones without annoying crosstalk. A
quiet office, for example, with a paging signal only, will not hear
foreground music playing in the lounge. The high capacity linear power
supply incorporates three independent secondary supplies with
independent bridge rectifiers and filters. The result is exceptionally
good crosstalk figures even with multiple channels driving full power
into 4 ohm loads.
No bad "spikes"
The MA 3 is
designed to operate without interruption of signal with as little as 85
VAC available (120 VAC unit). Even if the Amplifier is operating at
full power, the signal will not breakup as the AC line voltage drops to
85 VAC. If the AC line drops lower than 85 VAC the signal mutes without
"spikes." Once AC power is restored, the signal restarts quickly
without "spikes" or signal breakup.
The good "SPiKe"
The
power Amplifiers in the MA 3 are protected with National
Semiconductors' proprietary SPiKe* protection circuitry. SPiKe
protection offers a level of protection not available in conventional
amplifiers. It has the ability to instantaneously monitor the
temperature of the power device die, yielding a level of reliability
not achievable with discrete designs.
It's OK to light the 0 dB Headroom indicator a lot
The
high performance Limiter used in the MA 3 means all the available power
can be delivered to the load and not simply held in reserve to avoid
overload. There is no need to buy up to four times the required power
just to prevent occasional system overload. The MA 3 can compress a
signal with 9 dB of dynamic power range down to a signal with 3 dB of
dynamic power without loss of speech intelligibility or excessive
distortion.
With typical amplifiers, when 40 watts is needed
to achieve a required average SPL of 80 dB, the contractor must buy an
amplifier rated at no less than 160 watts just to maintain 6 dB of
headroom. The figure below illustrates the performance of the MA 3
Limiter.
*SPiKe is a registered trademark of National Semiconductor Corporation. Click here for more information
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