Hey all,
I’m building a mic preamp to interface a dynamic microphone with handheld radios and smartphone TRRS inputs. I’ve designed the following circuit to buffer the mic and improve audio quality while protecting from RF interference.
Use Case:
2N5088 NPN transistor for buffering/amplification
Will this work reliably with radio and phone inputs that provide ~5V through 2.2kΩ?
Is the transistor biased correctly with this setup, or does it need tweaking?
Is the signal level likely to be too low or too high for typical radio/smartphone mic inputs?
Any improvements for RF robustness or audio performance?
Can this safely be plugged into both radios and phones without harming either device?
Planning to build it on a prototyping board. I’d appreciate any feedback, especially from people who’ve built something similar!
I’m building a mic preamp to interface a dynamic microphone with handheld radios and smartphone TRRS inputs. I’ve designed the following circuit to buffer the mic and improve audio quality while protecting from RF interference.
Use Case:
- Works with dynamic mics
- Designed for radio mic inputs that supply 2-5V bias through ~2k-4.7kΩ (like Yaesu, Icom HTs)
- Also hoping it’ll work with smartphone TRRS jacks, which typically provide a similar bias voltage
2N5088 NPN transistor for buffering/amplification
- Ferrite beads (FB1, FB2) for RF filtering
- Bypass and AC coupling capacitors (C1–C5)
- No external power supply — powered only by bias voltage from device input
- I am using a M-87 5Ω dynamic mic, outputs around 0.05–0.11 mV @ 103 dB SPL
Will this work reliably with radio and phone inputs that provide ~5V through 2.2kΩ?
Is the transistor biased correctly with this setup, or does it need tweaking?
Is the signal level likely to be too low or too high for typical radio/smartphone mic inputs?
Any improvements for RF robustness or audio performance?
Can this safely be plugged into both radios and phones without harming either device?
Planning to build it on a prototyping board. I’d appreciate any feedback, especially from people who’ve built something similar!
