This repository contains schematics and PCB of a microphone preamp with switchable phantom power. It is based on the INA217 low-noise instrumentation amplifier. An additional buck-boost converter is needed for a phantom power higher than 12V.
| Reference | Quantity | Value | Note |
|---|---|---|---|
| C1 C3 C6 C7 C8 | 5 | 100n | Ceramic caps |
| C9 C10 | 2 | 10u | |
| C2 | 1 | 47u/50 | |
| C4 C5 | 2 | 47u/50** | Bipolar caps |
| D1 D2 D3 D4 | 4 | 1N4148 | |
| J1 | 1 | LED | Molex KK 2.54mm 2-pin connector |
| J2 | 1 | PHANTOM POWER | Molex KK 2.54mm 3-pin connector |
| J3 | 1 | MIC XLR | Molex KK 2.54mm 3-pin connector |
| J4 | 1 | PHANTOM POWER SW | Molex KK 2.54mm 3-pin connector |
| J5 | 1 | GAIN 10k | Molex KK 2.54mm 2-pin connector |
| J6 | 1 | OUT | Molex KK 2.54mm 2-pin connector |
| J7 | 1 | POWER | 10-pin IDC connector |
| R1 | 1 | 10k* | |
| R10 R11 | 2 | 10 | |
| R2 R3 | 2 | 6k8 | |
| R4 | 1 | 47k | |
| R5 R6 | 2 | 2k2 | |
| R7 | 1 | 100*** | |
| R8 | 1 | 1M | |
| R9 | 1 | 1k | |
| U1 | 1 | INA217 | DIP-8 package |
| U2 | 1 | TL071 | |
| 1 | XLR socket | Microphone input socket | |
| 1 | Output jack | ||
| 1 | 10k pot | ||
| 1 | Switch SPDT | ON-ON | |
| 1 | LED |
* LED current limiting resistor, change value according to used phantom power, 10k is for 48V
** use bipolar caps
*** adjust to change max. gain, smaller is more gain