The QA471 is the same product as the QA470, but with 10 dB of mic gain instead of 20 dB. The QA471 is a low-noise, fixed gain (10 dB ± 0.2 dB typical) microphone amplifier, with a switchable +48V phantom supply. The QA471 also features two general purpose amplifiers (with 30 and 10 dB of gain) based on ultra-low-noise OPA1612 opamps and powered from split ±12V rails, with nearly 18 dBV = 8 Vrms of signal output. The amplifiers inputs are AC coupled and can withstand up to 50V of DC, making them the perfect choice for measuring the noise on DC power supplies and LDOs.
When used with the QA401 and a calibrated microphone, you can read dBSPL directly from the display and make dBA measurements over a specified bandwidth. The 20 dB of mic gain was tailored to work ideally with most reference mics that exhibit around -40 dBV @ 94 dBSPL of sensitivity. Newer MEMS mics with 130 dB acoustic overload points will usually achieve -4 to -2 dBV at their overload point, which is readily handled by the QA471's wide output swing: The QA471's mic path delivers distortion numbers well below that of the mic even at 16 dBV output (-4 dBV input).
The phantom power on the QA471 is clean: The QA471 exhibits the same low-noise A-weighted measurement regardless of phantom power state. And the noise added by the mic amp is at the limit of the underlying amplifier, which is an SSM2019.
The solution is USB powered, and fully isolated from the USB power supply. If you are making acoustic measurements and need a precise, fixed-gain pre-amp for your setup, consider the QA471.