9
AC Power Connection
AC Connection is made through a standard Schuko or NEMA grounded plug. While
all models meet Safety Agency requirements for current consumption of less than 12
amp, 120 Vac during “normal” operation, peak current consumption can be higher
on the MPA1100 or MPA750.
The amplifiers can be wired for 100, 120, or 220–240 Vac, 50–60 Hz.
Some background on AC ratings is necessary to fully understand the limitations
on current draw. Essentially, there are three ratings of interest: (1) the legal operating
current as measured by the Safety Agencies, (2) the maximum expected average
under worst-case program material, and (3) the peak current draw at full output
power.
All major safety agencies around the world measure amplifier current and
temperature rise under the same “normal operating conditions” using a pink noise
signal with an average power equal to one eighth of maximum power. This was in
response to industry complaints that the former test level of one third power was
unrealistic for high-quality professional amplifiers. To put these levels in perspective,
music played at one third average power will be in a state of constant clipping, and
this power level is about the greatest one can obtain without completely obliterating
the program under clipping. The one eighth power level is about as loud as you can
play music while making some attempt to avoid obvious clipping.
We had to satisfy the following conditions:
1. Meet the safety agency requirements for “normal” current draw.
2. Remain within the functional limits of the plug for “severe program levels.”
3. Avoid unsafe conditions at full output power.
The AC consumption for each power level and load impedance is shown in
Table 1 and Table 2 (see pages 9 and 10).
The safety agencies are concerned with the current levels shown under the one
eighth power column. This is because building codes prohibit the connection of a
single load which exceeds 80% of the capacity of the branch circuit.
JBL Engineering standards call for ability to operate at one third power, in order
to meet the demands of “worst-case” heavily compressed, clipped program material.
This will use the AC current shown in the one third power column. The amplifier’s
protective circuits will not permit long-term operation at full power into 2 ohms.
Installation