The EasyEDA "Tesseract" DIY Guitar Practice Amplifier is an LM386 based low power amplifier designed to deliver up to about 500mW into an

8 Ohm speaker when run from a 9V battery.

Tesseract can be heard on YouTube here:

https://youtu.be/9XzodyefyV8

The design given here - which includes a complete PCB design and Bill of Materials - is highly flexible and allows the several options in both the build and use of the amplifier.

As well as a clipping circuit that some other designs - such as the more well known Smokey, Little Gem, Ruby and Noisy Cricket - have incorporated, Tesseract has several unique effects features designed into it:

  • Selectable Bipolar or Junction FET input stage for different input overload effects;
  • Adjustable gain and clipping 'hardness' in the Distortion stage;
  • An adjustable fullwave rectifier stage, driven by the distortion output, that generates a type of fuzz and frequency doubling effect called 'Wreckage';
  • An optional low frequency oscillator stage to sweep the Wreckage effect;
  • A simple mixer to blend the 'Wrecked' and the 'Distortion' outputs;
  • Selectable, adjustable low or high frequency boost (a type of tone control);
  • An important aspect of the design is that all the features and FX can be tweaked for your delight and delectation.
  • Most features are also optional and can be wire linked out if not required without affecting the other functions.
  • The design could easily be modified to suit the LM380 2.5W or LM384 5W amplifier chips (although the Boost function would have to be omitted) or a range of other devices.
  • The design also includes a headphone output jack.
  • The PCB includes dual footprinting to simplify the choice of some of the components.
  • All parts (excluding the PCB) are available from: http://www.bitsbox.co.uk/
    (Bitsbox can also supply suitable small switches, loudspeakers and battery holders or clips.)
    An alternative for J1 as an MPF102 is available from: http://www.tandyonline.co.uk/components/semiconductors/transistors/mpf102-jfet.html
  • Simulations of the different stages of this amplifier - and a copy of the EasyEDA LM386EE spice model used in them - can be found here:
https://easyeda.com/example/Tesseract_Guitar_Practice_Amp_simulation_files-H0ca8IFDB

The project was designed and simulated entirely in EasyEDA and Tesseract PCBs can be ordered direct from EasyEDA by forking the project:

https://easyeda.com/example/Tesseract_Guitar_Practice_Amp-MjP71jBni