Hello,
I am a little worried with my QA401 noise floor when I do mesurment from an class D amplifier. I don’t use the QA401 so often and last time it what 2 or 3 years ago for an home made class D amplifier.
Back then, I had a noise floor of around -110 dBV. I told myself I’d do a better job with the design next time.
Today, I measured an assembled TPA3255 260-2-29A module from 3E Audio, and to my surprise, I’m getting a noise floor of -115 dBV. Amirm from Audio Science Review tested this module (paired with a Mean Well power supply) and achieved much better results with his lab-grade equipment:
Noise floor around -140 dBV (with a 1 kHz peak at 0 dBV), THD+N of 0.0008%, and SINAD of 101 dB.
Me : Noise floor around -115 dBV (with a 1 kHz peak at 0 dBV), THD+N of 0.007%, and SINAD of 83 dB (with Hypex A180 power supply).
Same with my lab power supply
When I do the calibration test everything is OK. IN+ and IN- shorted to GND I have a noise floor of -145dbV (FlatTop and no attenuator). But it increase around DC (-110dBV).
When I link OUT+ to IN+ and IN- shorted to GND I have a noise floor of -155dbV (FlatTop) and a few harmonics
Any idea why I have this spike near DC and why the noise floor is so high?