QuantAsylum QA450 User’s Manual
Page 11
For 1 second, the spec has prescribed 25J (25W * 1sec @ 25C). For 100 mS, we see a single load resistor
can handle 10J of energy. Note that 1J = 1W for 1 second, and thus 10J = 100W for 100 mS. So, the array
of 8 resistors (when configured as a 4 ohm load) can handle 800W for 100 mS. If using as an 8 ohm load,
this this figure is 400W for 100 mS.
Tabularizing the observations above, we see the following:
The table above shows regions that may overstress the QA450 and should be avoided. For example, the
resistors would survive an 85 mS burst of audio
—
which is a 2K FFT @ 48Ksps
—
at 114W per R. This
would deliver 916W into the load. But this would result in 15.1A of connector current and 60Vrms.
These overstresses are marked in red. Limiting the max load power to 200W for 220 mS into 8 ohms and
4 ohms provides a reasonable reliability margin. This is an 8K FFT.
The temp sensing on the QA450 has a lag. If the load resistors are hit with 800W for 100 mS, then the
temperature of the resistor active area will climb very quickly while the temp sensor located 2-3 mm
away from the resistor body will remain unchanged. Because of this lag, the 200W figure must not be
exceeded as the QA450 won’t be able to protec
t itself quickly enough. But at power levels below 200W,
the QA450 can fully protect itself and you don’t need to worry about harming the
QA450.
Audio Bursts
The QA401 Audio Analyzer operates on bursts of audio. It is these bursted modes where the utility of
the QA401 and QA450 combine to allow thorough testing at high power levels.
The QA450 is obviously not the platform you’d chose for burning
-in amplifiers. But a test suite that has
an average power level of 4-5W can run continuously without stressing the QA450.
Low Temperature Operation
The temperature sensors used on the QA450 are absolute sensors with a tolerance /-1%. The
QA450 firmware expects to see a temperature of at least 5 degrees. This ensures the sensors are
properly communicating with the CPU. If the ambient temperature is near 5 degrees, the QA450 will not
allow load control.
