Has the QA403 output out-of-band residual signals?

QA40x
1

Found that my soundcards Creative E-MU 0204 and Tracker Pre emit residual waves in a out-of-band frequency region, around 100 kHz and higher. Since I work also with analog measurement instruments which go up to 1 MHz bandwidth these residuals distort low signal measurments. Is the QA403 much better in this sense?
Greetings to Matt,
Sven
Germany

2

Hi @Sven, the QA403 uses a ES9038 DAC, and modern converters are eons better than the converters popular 15 years ago. But, that said, I don’t think I’ve seen any ES9038 measurements out to 1 MHz–not even from ESS Tech. If you have that equipment and want to measure, I’d be curious to see. If it doesn’t meet your needs, of course we’d take it back and refund you the purchase price. And in your case, if you can post the measurements, any shipping + VAT + import fees + return mail fees you experienced.

What would you measure with? AP555B?

3

Hi Matt,
no, I can’t afford an AP. Have several meas tools like Sennheier UPM 550 which is an analog pointer instrument special audio measurement tool which goes to 1 MHz with 1 mV FS and up to 100 kHz FS range is -90 dB = 30µV. Also I have a Sound Technology ST 1710A which measures up to 100 kHz -80 dB FS which also my HP 8903B can do. For time based meas I have the HP 54616C scope which can go up to 500 MHz. I am an retired old school hp EE who has audio as a hobby and restores mainy electrontube based gear. Will try to get a QA403 from Elektor, but currently out of stock.

4

Hi @Sven, I’m pretty sure the out of band noise of the QA403 will beat all of those devices. In a 20 kHz bandwidth the ADC noise is about 1.3uVrms, and in a 95 kHz bandwidth it’s about 3.5uVrms. There could be some nasty stuff lurking up above 100k, but hopefully not enough to get to the level your UPM550 can measure.

5

Hi Matt, thank you for the information. Of course the performance values of the QA403 and other DACs today are better than my meas insturments. Since I do not develop 0,0001 % THD amplifiers it is sufficient when the DAC is so good not noticeably show up spuriious signals on my instruments which measure down to approx. 0.002 % THD. When will the QA403 be available again?