Colour Design Pt. 5: Finalizing the Colour Module Format November 14, 2013 13:55 3 Comments
Demonstrating how Colour works for the upcoming Kickstarter video. Photo by Zach Robbin.
Colour as a PlatformThere are four parts to a complete Colour unit: the Palette (motherboard) and three Colours (modules). The palette provides all of the power, I/O, control, and gain/attenuation circuitry to the colours, which provide the, well, color. (As an American, I spell 'color' with five letters. Co-designer Link Simpson is Canadian, hence the 'u'.) And while we're releasing three colours of our own with the palette, Colour is intended to be first and foremost a platform for the community to experiment with analog saturation circuits. Therefore, defining the specifics of the modular format was one of the most important and labored-over design decisions in the project. My design goals were for the colours to:
- have as much vertical clearance as possible for large components;
- make a solid mechanical connection with the palette;
- make a solid electrical connection with the palette;
- mount/dismount quickly and easily;
- be protected against being inserted backwards.
To address the first concern, I opted for 1/8" standoffs, so that the mounting surface for components on the colours was only 3/16" higher than the palette. This leaves .968" of clearance for colour components within the allowed 1.5" 500-series space, enough room for large caps and small transformers.
When I turned to choosing standoffs, I realized that design goals 2 and 3 stand in opposition to each other: in most cases, the sturdier the connector, the more time and work it takes to fasten and unfasten. After ordering and demoing several different snap- and screw-in standoffs, the one I found that married sturdiness and convenience most happily was the Keystone 9018 (pictured). The 9018 spacers allow the colours to be simply pressed in, instead of screwed, and the locking nylon tabs ensure the colour cannot be removed without squeezing the tabs together.
Finding the perfect electronic connector involved negotiating between another set of contradictory design goals: 1 and 3. By reducing the space between the colours and the palette to make room for big components on top of the colours, I had given away the space I needed below for the .100" pins and headers I had previously chosen for the electrical connectors. My first attempt at a solution was to remove the connectors altogether and place pads on the PCBs of the palette and colours themselves that would mate when the colours were screwed down. This would eliminate the need for spacers as well, since the colours could mount on the same standoffs as the palette PCB. And it would buy an extra 1/8" of clearance for the colour components!
The ill fated spacer- and connector-less colour mounting approach.[/caption] Unfortunately, it proved impracticable for a couple of reasons. First, it required large regions of the palette PCB to be routed out to provide clearance for the bottom of the colour PCBs. This compromised the structural integrity of the palette board and made wiring and grounding more risky. Second, the PCB pads simply did not mate very well. The connections between some pads were intermittent, depending on how thick the plating was on adjacent pads. So it was back to the now-familiar process of catalog digging, sample ordering, evaluating, and repeating. Except this time the process was almost a pleasure, since it turns out there is a company called Samtec kicking the connector industry's ass from here to next Tuesday. Samtec is the only electronics manufacturer or distributor I've come across with a truly functional, 21st-century website that makes it easy to find, sample, and buy their components. And they happen to make a .100" header sits on top of the PCB and mates with pins from below. Brilliant! Problem solved. (Note to other US/European manufacturers: give me a functioning website, phone support, and free samples and I will give you my money!)
The final colour mounting solution, with Keystone spacers and Samtec .100" connectors.[/caption] Finally, to meet design goal 5, I've offset the front row of electrical connectors so that the colours can only be inserted into the palette in one direction. This protects the colours from being destroyed by plugging the audio inputs into the power output connectors. This small revision will be implemented in the final PCB.