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Some background can be found in my SSR-01 project.

This design is based on my SSR-01 project and the goal was to make the pcb with hole mounted parts as versatile as possible.

Interesting features

1. 2-layer pcb with 70 um (2 oz.) copper.
2. Gold pads.
3. Extremely low noise.
4. Extremely low output impedance in the audioband.
5. Easy to change voltage
6. Well-known and well-tested in serious and demanding applications.
7. Option for TO92 or SOT23 transistors for the small signal transistors.
8. Option for DIL08 or SO08 opamp.
9. LM431 (and similar) reference or devices like LM329. The pcb has an universal footprint.
10. Trimming options for both the reference and the feedback. Room for extra resistors and trimpots.
11. Option for using three different kinds of smoothing caps, radial, axial or 10 mm snap-in.
12. Output with sense inputs.
13. All resistors 10 mm so it is possible to use a cut and bending machine for those parts.

Option for using higher voltage than the max supply voltage for the opamp.