Fork me on GitHub

Project Notes

#104 Ruby Guitar Amp

A version of the runoffgroove Ruby LM386 guitar amp.


The Ruby amp is similar to the LittleGem, however it introduces a JFET buffer on the input and discrete volume and gain controls.

The build here is based on the runoffgroove schematic, but with a few variations:

  • adds a coupling capacitor on the input
  • J201 n-channel JFET instead of the original MPF102



NB: in the schematic below, the FET symbol is not quite correct (shows n-channel MOSFET instead of JFET)

The Schematic

Breadboard Build

Running the amp on a breadboard is possible, but noise and interferance can be a real problem. So performace on a breadboard is not a very good indicator of actual performance if you build the circuit on a PCB.

The Build

Prototype Build

Running on a protoboard. Works really well! I need to find some pots to replace the trimmers then I can mount it properly.

Here’s the layout I used:

The Schematic

The Schematic

The Schematic

Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.