QuantAsylum QA451 User’s Manual
Page 8
Load Inputs
The load inputs are where the amplifier/DUT will connect. The loads are switched internally by relays
rated for 12A at 250VAC and 12A at 24VDC. The loads are DC coupled, but it’s expected that ONLY AC
signals will be presented to the QA451. Given the QA451 maximum ratings, the voltage on the load
inputs must not exceed 50VAC RMS
The maximum currents at the QA451 maximum ratings occur when the load is set to 4 ohms at 300W.
This corresponds to an 8.66A RMS current.
The Load Input connector on the QA451 is a Molex 39536-0004. The mating connector is a Molex 39534-
0004.
Do not exceed the 200W for 220 mS rating of the Amplifier Load subsystem.
BNC Outputs
The BNC outputs are single-ended attenuated version of the load inputs. The attenuation is 12 dB. This
means if your amplifier is 10 dBV = 3.16Vrms (as measured with DVM in AC mode across L+ and L-) and
the QA451 load is set for 8 ohms, then the QA451 will be dissipating (3.16^2)/8 = 1.24W. The BNC
outputs will measure 6 dB lower, which would be 4 dBV = 1.58Vrms
The 6
th
order low-pass filter in the QA451 has its corner at approximately 65 KHz. A SPICE simulation of
the output is shown below, with the 3 dB points marked. For Class D amplifiers with switching
frequencies between 200 and 500 kHz, the filter will provide significant attenuation of switching
products while still permitting a 3
rd
harmonic measurement to be made with a 20 kHz fundamental.
