Gain Problem on QA401

1

Hello,

I have a QA401 which I have been using for a few years. I usually just read the DUT gain off the QA401 PC screen and take that as the system gain, and this has always worked well for me. However, a customer with a very high output DAC asked me to reduce the system gain on some amps he bought, which I did. The main amp has a gain of 29.9 dB, and the front-end balanced-to-unbalanced buffer amp was set up for a gain of -10.5 dB. The gain reported by the QA401 PC screen in the final outgoing test was 19.6 dB.

The system was operated in balanced mode both from the QA401 DAC into the balanced input on the amp, and from the speaker output into the QA401 ADC. the QA401 attenuater was set to -20 dB

The problem is the customer is reporting a gain of 13.6 dB on his bench which is 6 dB lower than the reported QA401 gain.

What am I missing here?

Thanks

Andrew

2

Symmetrical setup gives a difference of 6dB in opposite of an unsymmetrical setup.

3

Yes, I understand that, but the reported gain on the QA401 PC screen should account for this, yes?

4

Hi Andrew,

Have you selected the +6.02dB gain compensation option? Perhaps this can be of some help?

https://forum.quantasylum.com/t/qa-403-power-readings-off-by-6db/1504?page=2