Sound Lab Mini Build Notes

I recently built a Sound Lab Mini-Synth from Before I start talking about the build, I want to say a few words about the SLM. It is awesome. It sounds fantastic and it has all of the basic building blocks of a "real" synthesizer. I think the reason they call it "mini" is that it is self-contained, not modular. Some people have built patched versions, but the standard configuration is to use switches. For instance, instead of using patch cords, the two oscillators, the filter and amplifier each have switches to enable LFO and envelope modulation. That is one of the reasons I think it makes a great first synthesizer.

Sound Lab Mini-Synth

If you are thinking about building it on a proto board, let me suggest that you buy the circuit board and save yourself a ton of time. It is only $35 and is well worth it. It is very easy to solder, even for a beginner. The parts are well spaced and the pads are large. My only complaint is that the control panel connections are not brought out to busses, but are scattered around the circuit board. That is pretty minor and the web site has well labeled diagrams of the circuit board.

I bought the kit which includes the circuit board and all necessary parts except the enclosure. So, the majority of my build time was spent designing the control panel layout.

I wanted it to be portable, with built-in batteries and a nice, clean consumer electronics feel rather than a bulky box or rack. So, I looked for an enclosure that had two 9V battery compartments and was big enough to accommodate all of the controls and the circuit board. The largest double 9V enclosure I could find was this one from Box Enclosures. I love the look of it and it is small enough to hold in one hand and fiddle with the controls with the other hand.

There are several panel layouts on the MFOS site, but none were suitable for this enclosure, which is pretty small and has a portrait rather than landscape orientation. I spend untold hours in Corel Draw until I had a layout I liked. I must say, I am very happy with the result.

The controls – sixteen knobs and twenty switches - all fit great in the available space, but the small interior of the enclosure presented some challenges. The enclosure is not rectangular. It has a scooped-out shape on the bottom (which you can see in the picture below). That makes it easy to hold, but cuts down on space for the circuit board. The only way to make it fit was at an angle. I put .875" PCB supports on one side of the board, and the other end just angles down to rest on the bottom of the enclosure. Side-to-side, the board fits exactly between the enclosure’s built-in PCB mounts. It is a tight enough fit that it does not move around when closed and does not need to be screwed or glued into place. Oh, yes, I also had to put it in upside down! The components on the board would touch the pots and switches on the control panel.

Space constraints also dictated that I use 1/8 inch instead of 1/4 inch jacks. The SLM has four jacks: audio out, trigger/gate in, and a CV in for each of the two oscillators. There is another jack-related constraint. The enclosure is thick plastic, so you will need jacks with very long threaded bushings. The ones I used were not long enough, so I had to counter sink the retaining nut. The result actually looks pretty cool because the jacks are flush against the case.

There are a lot of connections between control panel components, and even a few resistors and capacitors mounted right on the pots and switches. The MFOS site has a wiring diagram that corresponds to the "standard" panel layout. I made my own diagram for my new layout and I used the same colors and annotations as the MFOS diagram for consistency.

I did all of the control panel wiring with 22 gauge solid core wire. That worked well because all of those wires need to be out of the way of the wires that connect to the PCB and solid core wire can be pushed up against the panel and does not move. I color coded the wiring using the conventions from the SLM documentation, which is: black ground, red +V and green –V. I used yellow wires for intra-component connections. The wire is telephone wire which conveniently comes in those four colors. I use the larger gauge stranded wire that comes with the kit for panel to PCB connections. Those are also color coded for easy tracing but not to any kind of standard. One thing I would do differently with regard to wiring would be to make it neater. I would group the wires into two bundles and route them along the left and right of the panel and board. To do that would take more wire than came with the kit, but wire is cheap.

The final step was to print out the panel background on a vinyl sticker and cut out the holes on my digital cutter.

For anyone else who might want to use my layout, here is a PDF that has the background/drill template as well as the panel wiring diagram and a version of the annotated PCB that shows all of the connections on the bottom of the circuit board.

Here is what it looked like just before screwing the enclosure shut. Yes, it really all fits!

Sound Lab Mini Interior