DIY microphone kit inspired by the legendary U47 FET discrete topology. This kit is designed for the audio enthusiast who wants professional-grade studio results without the multi-thousand dollar price tag.
Note on Authenticity: While the circuit is a faithful recreation of the original U47 FET amplifier stages (with modern improvements for biasing and stability), this is not a 1:1 clone. This kit is designed to provide exceptional performance using high-value, accessible components. For those seeking maximum historical accuracy, the PCB is fully compatible with factory Neumann capsules and BV13-style transformers, which would bring the frequency curve even closer to the original 1970s specifications.
Faithful Topology: Maintains the discrete bipolar amplifier stages and JFET head-amp of the original.
Premium PCB Design: High-quality board featuring an unmasked, grounded guard ring around the ultra-high impedance bias section to ensure a dead-quiet noise floor.
Modern Biasing: Includes an adjustable trimmer (RV1) and corrected resistor values (R6) to allow for precise calibration of the 22.5V JFET drain bias.
Purist Signal Path: The -10dB pad has been removed to simplify the signal path and improve headroom.
Bass Roll-Off: Includes a jumper-selectable High Pass Filter.
Capacitors: WIMA Film Caps, Polystyrene HF filtering, and Low ESR Electrolytics for the power rails.
Resistors: 1/4W Metal Film (1% tolerance).
Transistors: Low-noise BC550C/BC560C series and 2N3819 JFET.
Frequency Response: ~40Hz – 16kHz
Power Requirement: 48V Phantom Power.
Output: Balanced XLR
PCB
Complete set of tested electronic components (Resistors, Capacitors, Transistors).
This is a DIY project. While I provide a comprehensive digital build guide, successful completion requires solid soldering skills and basic knowledge of a digital multimeter. I have tested this circuit extensively to ensure professional results when built correctly.
Support: I am a seasoned audio builder and editor. If you run into technical hurdles during your build, I am happy to provide reasonable email support to help you get your mic in the booth!