Cloud Electronics MPA626 - Manual (Page 15)

14 MPA-626: Installation and Operation Manual
17 General Notes
17.1 Multi-zone Applications
Where the sound system specification calls for separate control in several zones, the MPA-626
can be used in multiples. Signal sources can be connected to several inputs as required, but
care must be taken to ensure the output stage of the signal source is capable of driving the
lower impedance load. Line input impedance is 47k
Ω and it is reasonable to assume that most
op-amp based signal sources should drive a 10k
Ω load, thus allowing up to five parallel circuits.
The input impedance of the microphone amplifier is 2.4k
Ω making it suitable for a microphone
with a maximum impedance of 600
Ω. A single 200Ω microphone could therefore be connected
to three balanced inputs. To avoid any problems associated with differences in mains supply
earthing, we recommend that all MPA-626's used in a multi-zone application should be located
close together and connected to a common mains supply. Note that when using MPA-626 in
multiples in a 19” rack, ventilation provisions must be made to ensure that the hot air rising from
the ventilation slots of one MPA-626 does not rise up into the unit above it.
17.2 EMC Considerations
The MPA-626 fully conforms to the relevant electromagnetic compatibility (EMC) standards and
is technically well behaved. You should experience no problems interfacing the unit to other
items of equipment and under normal circumstances, no special precautions need to be taken.
If the unit is to be used within close proximity to potential sources of HF disturbance such as
high power communication transmitters, radar stations and the like, it is suggested that the
cable screen be connected to the shell of the XLR type connector and the line input signal leads
be kept as short as possible. Always use balanced interconnections wherever possible. If the
MPA-626 is mounted in a 19" rack, do not locate the unit in close proximity to a powerful
amplifier, which may radiate a strong magnetic field from the power transformer.
The 0V rail of the MPA-626 is coupled to the chassis ground by a parallel resistor/capacitor
network and no interconnection problems should be encountered. When several mains powered
units are connected together via their signal cables, there is a risk of one or more earth loops
which may cause an audible hum on the system even with the gain controls set to minimum.
The 'hum' can be remedied in several ways; the preferred method is to operate interconnects in
the balanced mode wherever possible, with the cable screen only connected at the receiving
end (amplifier input). The signal source units should be located as close as possible to the
MPA-626 and the metal housing of the various units should not be electrically connected
together through the equipment rack. If this is a problem, rack isolating kits are available from
specialist hardware suppliers. If the problem persists, try to connect all interconnected units,
including power amplifiers to a common power source to ensure a common ground is provided.
The MPA-626 is convection cooled and requires adequate space to allow a free flow of air
through the unit. In 19” rack applications we recommend leaving 1U of rack space above and
below. In free standing applications we recommend fitting the feet supplied and placing the unit
on a flat surface and leaving the ventilation slots on top of the unit free from any obstructions.
Line inputs
-3dB 20Hz/70Hz selectable -20kHz
±0.5dB
<0.02% 1kHz
195mV (-12dBu) to 2.0V (+8dBu)
17.3 Earthing
17.4 Ventilation
18 Technical Specifications
Frequency Response
Distortion
Sensitivity
Input Gain Control
20dB range
Input Impedance 47k
Ω
Headroom >20dB
Noise -89dB 22Hz –22KHz, at speaker output relative to 150W into 4
Ω
Equalisation HF:
±10dB/10kHz LF: ±10dB/50Hz
11-07-02 V4