Microphone Preamp Card for Harrison Mr4 Console

This is a replacement/upgrade for the Harrison Mr4 preamp card. These cards have not been produced for quite some time, and if one goes bad, it is not replaceable.

The original cards were etched with no solder mask, and in many cases a simple recap can damage or lift the solder pads. Additionally, if any damage happens to the integrated resistor network, this bespoke part cannot be replaced. While it is extremely unlikely the resistor network will fail from an over voltage or over current situation, it is far more likely that they will fail from excess moisture conditions (green corrosion is usually a sign of this near the pins).

This design instead uses discreet resistors, and can be readily serviced should anything happen to the circuit. The traces and pads are also more robust in this design and should survive any re-capping in the future with no problem. Transistor sockets have also been added, in the event of a failure, or if the user wants to substitute different transistors in the preamp.

Great care was taken for the layout of this. No vias have been used, and all traces cross at 45 degree angles. All empty space has been filled with ground plane, leading to an excellent noise floor.
Please feel free to ask any questions!