QA403 Calibration Verification

There is a new post up on the wiki on how to verify the calibration of your new QA403 (and QA402). This can be a great way to familiarize yourself with the operation of the QA403 when it arrives. If you aren’t seeing a flatness like what is shown at the link, we’d love to know…The plot takes about 30 seconds to create.

@matt, just got my QA403. Thx. Ran the tests.
All outputs .997-.998 @1khz
Here is the graph though. Channels differ across entire spectrum

Thanks for sharing @Moto. From your plot I extended some areas and then pasted above to see on the scale. Your relative flatness looks to be within about 0.01 dB (0.11%), or roughly +0.006 and -0.004 dB off of 0. That is over 40 dB of DAC relay gain changes and and 42 dB of ADC relay gain changes. Nice.

Can you share your DVM model? I suspect your DVM is dead-on for 60 Hz, and has rolled off about 0.3% at 1 kHz and 2% at 20 kHz. That quite good if it’s a handheld.


It’s a 10 year old fluke 88. I will put it on the bench tomorrow and test with better dvm.
Will also repeat tests with my QA402.

Tested with a 4 1/2 digit dvm.
QA403 60hz .999-1.0
1000hz .999-1.0
20000hz .997-.998
60hz .999-1.0
1000hz 1.0
20000hz .961-.962
Based on the dvm seeing almost 1v @20000 on the QA403, it would seem that the low voltage .961@20k on the QA402 is real.

Here is gain test on QA402. Slightly better than QA403 but insignificant.

@matt have the relays in the qa403 changed? I don’t get the loud clicking when changing attenuation levels that I get in my qa402.

Hi @Moto, it is the same on the output. So, starting at 18 dBV and moving down (eg 17, 16, 15…) you will hear them about every 10 dB until you are around -12 dBV or so, and at that point the relays will stop changing. That is unchanged from QA402.

On the input, you will hear a change as you switch from atten off (0, 6, 12, 18) to atten on (24, 30, 36, 42). That is, 0 to 24 and back to 0 will yield a click on each change. As will 0 to 42, and back to 0.

But as you move from 0 to 6 or 12 or 18 (or any level in that group), that is all handled by solid state switches so there’s no click. I really miss the clicks…

DHL delivered my QA403 today. Nice! I thought I would follow the advice to familiarize myself with the QA403 Verifying Calibration · QuantAsylum/QA40x Wiki · GitHub.
I left the QA403 on for about 1 hour before taking the measurements.

First measurement: check flatness. Here is the result:

looks good to me.
At this point I verified the outputs of the QA403 using a DVM UNI-T UT61E a 4 1/2 digit. Measurements were made at 50Hz and 1KHz setting the QA403 generator at 0dBV.

The results are: L @50 Hz 1.0002V; L @1KHz 0.9999V
R @50Hz 1.0000V R @1KHz 1.0004V

The least significant figure of the DVM was quite stable and in any case fluctuated little.

Finally I checked the attenuator relays: here is the result:

To me the results seem very good. I am very satisfied with the QA403!

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