QA402 User Manual
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Atten LED: This indicates the QA40x input attenuator is active. If you are going to connect the QA40x hardware
to large signal, it is best to pick one of the higher input ranges that enable the input attenuator as you attempt
to learn the characteristics of the signal you are measuring. This is especially true if you are measuring
equipment that is being repaired that might have potentially unexpected outputs behavior. The LED allows you
to readily see if the input attenuator is active, ensuring the QA402 can protect itself from unexpected inputs.
Expansion Connector
The QA403 and QA402 have slightly different front-panel connector pinouts. The expansion connector for the
QA402 is a 2x8 pin male connector with a 1.27 mm pitch. As you face the connector and front-panel, the
connector pin out appears as follows:
The front-panel connector currently supports driving Generator 1 and/or 2 DAC output sines at 16- or 32-bit
widths at 48 kSPS. I2C, ADC input, and sample rates other than 48 kSPS are not currently supported, but may
be added in the future. More information and schematics for use with the front panel expansion connector
can be found on the QA40x.
BNC Inputs and Outputs
The QA40x hardware has 4 outputs, or both left and right differential pairs. The + and – signals are always
complementary. That is, when the L+ signal is rising, the L- signal is falling. Viewed on a scope, the + and –
signals are always moving in equal but opposite directions.
The left and right outputs largely work in unison, but there are certain modes (for example, muting or external
waveforms from an API) where the left and right outputs can work independently.
Most consumer gear will take a single-ended input and output signal. Pro-audio will often take a differential
signal. Differential signals are commonly used in noisy environments because interfering signals that appear
on both inputs simultaneously are “cancelled” or at least greatly attenuated. However, for much of your audio
work, you may prefer to use the device in single-ended mode especially if you are working on line-level
consumer audio type equipment. If you wish to use the inputs single ended, then you can use a BNC terminator
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