MFOS Weird Sound Generator in SMT

Here comes my next conversion of Ray’s classic analog synthesizer, the Weird Sound Generator!

Eurorack version of MFOS Weird Sound Generator, with prototype laser etched front panel

This is the same process as for my previous SMT/Eurorack conversion of the Sound Lab Mini-Synth. The circuit is identical to the original, including component references.

General description

The WSG is a simple drone-weird-thing for fun and a lot of sounds. There’s just one output and no CV input. Its simplicity makes it a very good candidate for beginners.

The WSG contains 2 voices and one filter.
Each Voice contains 3 oscillators. Zany is a LFO. The two others are the drones:Weird and Wacky. Weird can be modulated by the LFO Zany (through Zaniness control potentiometer) and also can be “interfered” by Wacky if Wackiness switch is activated. Unusual switch changes the Zany modulation of Weird from square to almost triangle.

Voice A and B share the exact same behavior.

The circuits

I redrawn and rearranged the schematic layout.

Ray’s schematics are sometimes convoluted and hard to read (very long wires, lot of crossings etc.)
Besides the fact that I needed to redraw the schematics into KiCad before laying out the new PCB, redrawing them gave me the opportunity to better understand the circuits.

MFOS WSG, Voice A
The filter section, with output buffer

The next circuit is the Low Pass Filter. It only uses one Op Amp. The second Op Amp is for output amplification. It might be necessary to increase slightly the output level by modifying Rb/Rf values. See annotations on schematics for possible values.

Redrawn MFOS WSG schematics for SMT conversion (wsg-1.1-20181009.pdf)

BOM

Interactive BOM

Front Panel

The panel layout is somewhat different from the classic one. I chose to put the controls in a vertical arrangement. While it keeps the initial spirit, the new arrangement results in a very compact 18HP wide only Eurorack module.

18HP Eurorack Front Panel for MFOS WSG
MFOS WSG in SMT – 3D render

One big advantage over the initial version is the complete lack of wiring chore. Everything sits on one PCB. Surface mount components are located on the bottom side.

Side view of the WSG. No wiring required!
Bottom side of the SMT/Eurorack MFOS WSG

There’s only few components in this project, which makes it ideal for a fun and easy first step into the Surface Mount Technology.

Two kludge areas have been added for your own safety.
All the important signals are available and labelled on PCB sides, allowing you to poke around and ease your circuit bending needs.

More!

For more descriptions about the circuits, and real “Weirdsoundology” studies, please visit the original WSG pages by Ray Wilson.

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