#104 Ruby Guitar Amp

A version of the runoffgroove Ruby LM386 guitar amp.

Notes

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

Construction

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

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.

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:

Credits and References

• Ruby 386-based 9v battery amp
• LM386 datasheet
• J201 datasheet