An Ultralow-Noise Phantom-Powered Microphone Amplifier

Spinelli EM. An Ultralow-Noise Phantom-Powered Microphone Amplifier. J Audio Eng Soc. 2026;74(11):877-886. doi:10.17743/jaes.2026.0312

@article{Spinelli2026_23506,
  author = {Spinelli, Enrique M.},
  title = {{An Ultralow-Noise Phantom-Powered Microphone Amplifier}},
  journal = {Journal of the Audio Engineering Society},
  volume = {74},
  number = {11},
  pages = {877--886},
  url = {https://doi.org/10.17743/jaes.2026.0312},
  doi = {10.17743/jaes.2026.0312},
  year = {2026},
  month = nov,
  publisher = {Audio Engineering Society}
}

TY  - JOUR
TI  - An Ultralow-Noise Phantom-Powered Microphone Amplifier
AU  - Spinelli, Enrique M.
T2  - Journal of the Audio Engineering Society
J2  - J. Audio Eng. Soc.
VL  - 74
IS  - 11
SP  - 877
EP  - 886
PY  - 2026
DA  - 2026/11/10
DO  - 10.17743/jaes.2026.0312
UR  - https://doi.org/10.17743/jaes.2026.0312
PB  - Audio Engineering Society
LA  - en
AB  - Low-noise amplifier design inherently conflicts with low power consumption. This trade-off becomes particularly critical in phantom-powered audio equipment, where the available power is severely limited and must be carefully preserved. An optimized design for achieving ultralow-noise amplifiers with a noise floor below 1 nV/√Hz while operating under phantom power is presented. It is shown that, when the total collector current is limited, paralleling N transistors to reduce amplifier noise is effective only up to a certain number of devices, beyond which increasing N no longer improves noise performance. As an example, a double-balanced microphone amplifier was designed, built, and tested. It exhibits an input-referred noise density of 0.6 nV/√Hz over the 20 Hz–20 kHz bandwidth (−141 dBV or −139 dBu) while consuming less than 8.5 mA. A noise floor level of 0.55 nV/√Hz (−140 dBu) can be achieved by accepting a phantom current of 9.5 mA. A detailed circuit analysis and design equations are provided to adapt the circuit to different requirements and design constraints.
ER  -