QA470 Low Noise Mic Pre-amp [Retired]
NOTE: The QA470 has been replaced by the QA471, which is the same product with 10 dB of mic gain instead of 20 dB. There were many cases where mics with high acoustic overload points (AOPs) were requiring the attenuator to be engaged on the QA401 at 125 to 130 dBSPL. The lower gain will help with that. Since the QA401 input noise floor is -115 dBV (20 kHz, no weighting), there's still plenty of margin to measure the at the noise floor even with just 10 dB of gain. The QA471 will be begin shipping the week of September 14.
The QA470 is a low-noise, fixed gain (20 dB ± 0.2 dB typical) microphone amplifier, with a switchable +48V phantom supply. The QA470 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 the 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 QA470's wide output swing: The QA470'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 QA460 is clean: The QA460 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 QA470.