Specifications

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strapping their chassis together. CAUTION! The outer shell of the DC intercon-
nect cables is positive relative to the chassis. Do not allow a DC cable plugged
into a powered unit to hang loose where it might short against the chassis or rack
frame.
MAINTENANCE
There is no routine maintenance required. If you have a problem, check the pan-
el LED indicators to assure that the units have DC power, eliminate by substitu-
tion microphones, input and output cables, connectors, downstream devices,
Mixer-to-Expander interconnect cables and power supplies. If all else fails, read
your warranty (even though it probably ran out yesterday) and call us for sympa-
thy and overpriced parts.
POWER SUPPLY LEVELS
The recommended loaded DC input voltage range is 22 to 30VDC over the full
range of AC line voltage tolerances. The audio circuits continue to work with re-
duced headroom below 22VDC but the LED VU meter will not indicate the top
segments. Momentary surges up to 36VDC will cause some increased internal
heating, but above 36VDC call our parts department for some of those expensive
ICs.
OPERATING POINTS
An internal reference voltage equal to 1/2 the supply voltage is generated by A9
in the MX100 and A5B in the XP100. All audio stage inputs and outputs should
show a DC level equal to this voltage when measured with a high impedance
meter. XLR audio inputs and outputs are capacitor coupled and ground refe-
renced. The expansion buss input is at this DC reference level and must not be
accidentally grounded by dangling audio interconnects cables.
METER CALIBRATION
To set, adjust the Master Gain Control for the desired 0VU output level in the
range of +8 to -10dBm (+4dBm nominal) with an independent audio voltmeter.
Adjust the internal meter calibration trimpot, R70, for 0VU indication on the bar-
graph meter.